1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Table of Contents Chapter 2 Matter and Energy Section 1 Energy Section 2 Studying Matter and Energy Section 3 Measurements and Calculations in Chemistry

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Energy Bellringer Work in small groups to brainstorm ideas relating to energy. List different types of energy, list why energy is important, and when energy is released or absorbed. After brainstorming for five minutes, examine your lists and write your own definition for energy. Chapter 2

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Explain that physical and chemical changes in matter involve transfers of energy. Apply the law of conservation of energy to analyze changes in matter. Distinguish between heat and temperature. Convert between the Celsius and Kelvin temperature scales. Section 1 Energy Chapter 2

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change Energy is the capacity to do some kind of work, such as moving an object, forming a new compound, or generating light. Energy is always involved when there is a change in matter. Section 1 Energy Chapter 2

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Changes in Matter Can Be Physical or Chemical Ice melting and water boiling are examples of physical changes. A physical change is a change of matter that affects only the physical properties of the matter. For example, when ice melts and turns into liquid water, you still have the same substance represented by the formula H 2 O. Only the physical state of the substance changed. Section 1 Energy Chapter 2

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Changes in Matter Can Be Physical or Chemical, continued In contrast, the reaction of hydrogen and oxygen to produce water is an example of a chemical change. A chemical change is a change that occurs when one or more substances change into entirely new substances with different properties. A chemical change occurs whenever a new substance is made. The water, H 2 O, is a different substance than the hydrogen, H 2, and oxygen, O 2. Section 1 Energy Chapter 2

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Every Change in Matter Involves a Change in Energy All physical and chemical changes involve a change in energy. Sometimes energy must be supplied for the change in matter to occur. For example, for ice to melt, energy must be supplied so that the particles can move past one another. Section 1 Energy Chapter 2

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Every Change in Matter Involves a Change in Energy, continued Another example of a change in which energy must be added is when liquid water changes to form gaseous water vapor. Evaporation is the change of a substance from a liquid to a gas. Imagine a pot of water on the stove. When energy is supplied by the stove, the water evaporates, or turns into water vapor. Section 1 Energy Chapter 2

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Every Change in Matter Involves a Change in Energy, continued Some changes in matter release energy. For example, the explosion that occurs when hydrogen and oxygen react to form water is a release of energy. Heat energy and light energy are released as the reaction takes place. Section 1 Energy Chapter 2

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Endothermic and Exothermic Processes Any change in matter in which energy is absorbed from the surroundings is an endothermic process. The melting of ice and the boiling of water are examples of physical changes that are endothermic. The reaction that occurs when barium hydroxide and ammonium nitrate are mixed is an example of a chemical change that is endothermic. As the chemicals react, energy is absorbed. Section 1 Energy Chapter 2

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Endothermic and Exothermic Processes, continued Any change in matter in which energy is released is an exothermic process. The freezing of water and the condensation of water vapor are two examples of physical changes that are exothermic processes. The burning of paper and the explosive reaction between hydrogen and oxygen to form water are examples of chemical changes that are endothermic processes. Section 1 Energy Chapter 2

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Endothermic and Exothermic Processes, continued Energy can be absorbed by the surroundings or released to the surroundings, but it cannot be created or destroyed. The law of conservation of energy states that during any physical or chemical change, the total quantity of energy remains constant. In other words, energy cannot be destroyed or created. Section 1 Energy Chapter 2

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Law of Conservation of Energy Visual Concepts Chapter 2 Click below to watch the Visual Concept. Visual Concept

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Energy Is Often Transferred To keep track of energy changes, chemists use the terms system and surroundings. A system consists of all the components that are being studied at any given time. In the reaction between barium hydroxide and ammonium nitrate, the system consists of the mixture inside the beaker. Section 1 Energy Chapter 2

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Energy Is Often Transferred, continued The surroundings include everything outside the system. In the reaction between barium hydroxide and ammonium nitrate, the surroundings consist of everything else including the air both inside and outside the beaker and the beaker itself. Section 1 Energy Chapter 2

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Energy Is Often Transferred, continued Energy is often transferred back and forth between a system and its surroundings. An exothermic process involves a transfer of energy from a system to its surroundings. An endothermic process involves a transfer of energy from the surroundings to the system. In every case, the total energy of the systems and their surroundings remains the same. Section 1 Energy Chapter 2

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Conservation of Energy in a Chemical Reaction Section 1 Energy Chapter 2

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Energy and Change, continued Energy Can Be Transferred in Different Forms Energy exists in different forms, including chemical mechanical light heat electrical sound The transfer of energy between a system and its surroundings can involve any one of these forms of energy. Section 1 Energy Chapter 2

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat Heat is the energy transferred between objects that are at different temperatures. Heat energy is always transferred from a warmer object to a cooler object. For example, when ice cubes are placed in water, heat energy is transferred from the water to the ice. Energy is also transferred as heat during chemical changes. Section 1 Energy Chapter 2

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Energy Can Be Released As Heat An explosion provides an example of energy being released during an exothermic reaction. All of the energy that is released comes from the energy that is stored within the reacting chemicals. When a chemical reaction involves an explosion, it can make a loud sound, generate great amounts of heat, or send objects flying. Section 1 Energy Chapter 2

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Energy Can Be Released As Heat, continued During the explosion, the sound results from the generation of sound energy. The movement of the flying objects results from kinetic energy. Kinetic energy is the energy of an object that is due to the object’s motion. Section 1 Energy Chapter 2

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Energy Can Be Absorbed As Heat In an endothermic reaction, energy is absorbed by the chemicals that are reacting. For example, sodium bicarbonate, a chemical in baking soda forms three substances when heated. It becomes sodium carbonate, water vapor, and carbon dioxide gas, in the following endothermic reaction: 2NaHCO 3  Na 2 CO 3 + H 2 O + CO 2 Section 1 Energy Chapter 2

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Heat Is Different from Temperature Temperature indicates how hot or cold something is. Scientists define temperature as a measurement of the average kinetic energy of the random motion of particles in a substance. The transfer of energy as heat can be measured by calculating changes in temperature. Section 1 Energy Chapter 2

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Heat Is Different from Temperature, continued Imagine that you are heating water on a stove. The water molecules have kinetic energy as they move. Energy transferred as heat from the stove causes these water molecules to move faster. The more rapidly the water molecules move, the greater their average kinetic energy. As the average kinetic energy of the water molecules increases, the temperature of the water increases. The temperature change of the water is a measure of the energy transferred from the stove as heat. Section 1 Energy Chapter 2

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Temperature Is Expressed Using Different Scales Thermometers are usually marked with the Fahrenheit or Celsius temperature scales. A third temperature scale, uses the unit Kelvin, K. The zero point on the Celsius scale is designated as the freezing point of water. The zero point on the Kelvin scale is designated as absolute zero, the temperature at which the minimum average kinetic energies of all particles occur. Section 1 Energy Chapter 2

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Temperature Is Expressed Using Different Scales, continued At times, you will have to convert temperature values between the Celsius and Kelvin scales. Use the following equations in such conversions: t(°C) = T(K)  273.15 KT(K) = t(°C) + 273.15°C The symbols t and T represent temperatures in degrees Celsius and in kelvins, respectively. Section 1 Energy Chapter 2

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Temperature and Temperature Scale Visual Concepts Chapter 2

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Transfer of Heat May Not Affect the Temperature The transfer of energy as heat does not always result in a change of temperature. For example, consider what happens when energy is transferred to a mixture of ice and water. As energy is transferred as heat to the ice-water mixture, the ice cubes will start to melt. The temperature of the mixture remains at 0°C until all of the ice has melted. Section 1 Energy Chapter 2

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Transfer of Heat May Not Affect the Temperature, continued Once all the ice has melted, the temperature of the water will start to increase until it reaches 100°C. As the water boils, the temperature remains at 100°C until all the water has turned into a gas. The temperature remains constant during the physical changes in this system. Section 1 Energy Chapter 2

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Transfer of Heat May Not Affect the Temperature, continued During these physical changes, the energy that is transferred as heat is actually being used to move molecules past one another or away from one another. This energy causes the molecules in the solid ice to move more freely so that they form a liquid. This energy also causes the water molecules to move farther apart so that they form a gas. Section 1 Energy Chapter 2

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heating Curve for Water Section 1 Energy Chapter 2

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Transfer of Heat Affects Substances Differently If you transfer the same quantity of heat to similar masses of different substances, they do not show the same increase in temperature. This relationship between energy transferred as heat to a substance and the substance’s temperature change is called the specific heat. The specific heat of a substance is the quantity of energy as heat that must be transferred to raise the temperature of 1 g of a substance 1 K. Section 1 Energy Chapter 2

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Heat, continued Transfer of Heat Affects Substances Differently, continued The SI unit for energy is the joule (J). Specific heat is expressed in joules per gram kelvin (J/gK). Metals tend to have low specific heats. Water has an extremely high specific heat. Section 1 Energy Chapter 2

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Specific Heat Capacity Visual Concepts Chapter 2 Click below to watch the Visual Concept. Visual Concept

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Studying Matter and Energy Bellringer Write a brief paragraph describing your concept of the scientific method. Chapter 2

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Describe how chemists use the scientific method. Explain the purpose of controlling the conditions of an experiment. Explain the difference between a hypothesis, a theory, and a law. Section 2 Studying Matter and Energy Chapter 2

37. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method The scientific method is a series of steps followed to solve problems, including collecting data formulating a hypothesis testing the hypothesis stating conclusions A scientist chooses which set of steps to use depending on the nature of the investigation. Section 2 Studying Matter and Energy Chapter 2

38. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Method Visual Concepts Chapter 2 Click below to watch the Visual Concept. Visual Concept

39. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Method Section 2 Studying Matter and Energy Chapter 2

40. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Experiments Are Part of the Scientific Method The success of the scientific method depends on publishing the results so that others can repeat the procedures and verify the results. An experiment is the process by which scientific ideas are tested. For example, both manganese dioxide and beef liver cause a solution of hydrogen peroxide to bubble. You might conclude that the liver contains manganese dioxide. To support your conclusion, you would test for the presence of manganese dioxide in the liver. Section 2 Studying Matter and Energy Chapter 2

41. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Experiments May Not Turn Out As Expected Your tests would reveal that liver does not contain any manganese dioxide. Scientists often find that their results do not turn out as expected. Such cases are not failures. Rather, scientists analyze these results and continue with the scientific method. Unexpected results often give scientists as much information as expected results do. Section 2 Studying Matter and Energy Chapter 2

42. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Scientific Discoveries Can Come from Unexpected Observations Some discoveries have been made by accident, such as the discovery of a compound known as Teflon®. Teflon is the nonstick coating used on pots and pans. Its properties of very low chemical reactivity and very low friction make it valuable in many applications. Teflon was discovered when a scientist made a simple observation. Section 2 Studying Matter and Energy Chapter 2

43. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Teflon Was Discovered by Chance In 1938, DuPont chemist Dr. Roy Plunkett, was trying to produce a new coolant gas to use as a refrigerant. He wanted to react a gas called tetrafluoroethene (TFE) with hydrochloric acid. He recorded the mass of a cylinder of TFE. He then opened the cylinder to let the TFE flow into a container filled with hydrochloric acid, but no TFE came out of the cylinder. Section 2 Studying Matter and Energy Chapter 2

44. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Teflon Was Discovered by Chance, continued Because the cylinder had the same mass as it did when it was filled with TFE, Plunkett knew that none of the TFE had leaked out. When he opened it, he found only a few white flakes. Plunkett analyze the white flakes and discovered that the TFE molecules joined together to form a long chain of polytetrafluoroethene (PTFE). These long-chained molecules were very slippery. Section 2 Studying Matter and Energy Chapter 2

45. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Synthetic Dyes Were Also Discovered by Chance In London, England in 1856, the discovery of the dye aniline purple was made unintentionally by an 18-year-old student named William Perkin. Perkin was experimenting to a way to make quinine, a drug used to treat malaria. One of his experiments resulted in a product that was a thick, sticky, black substance. Section 2 Studying Matter and Energy Chapter 2

46. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Scientific Method, continued Synthetic Dyes Were Also Discovered by Chance, continued Perkin could tell that the substance was not quinine. In trying to wash away the substance, he made an unexpected discovery. Analyzing an Unexpected Discovery Pouring alcohol on the substance turned it purple. He named his accidental discovery “aniline purple,” but the people of Paris soon renamed it mauve. Section 2 Studying Matter and Energy Chapter 2

47. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations Questions that scientists hope to answer often come after they observe something carefully in the natural world or in a laboratory. Once observations are made, they must be analyzed. Scientists look at the data they have gathered for patterns that might suggest an explanation for the observations. A hypothesis is a reasonable and testable explanation for observations. Section 2 Studying Matter and Energy Chapter 2

48. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Chemists Use Experiments to Test a Hypothesis Once a scientist has developed a hypothesis, the next step is to test the validity of the hypothesis. The testing is often done by carrying out experiments. Imagine that you have observed that your family car has been getting better mileage. You state that a new brand of gasoline is the cause. You’ve made a hypothesis to explain an observation. Section 2 Studying Matter and Energy Chapter 2

49. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Scientists Must Identify the Possible Variables To test the validity of your hypothesis, your next step is to plan your experiments. You must begin by identifying as many factors as possible that could account for your observations. A factor that could affect the results of an experiment is called a variable. A scientist changes variables one at a time to see which variable affects the outcome of an experiment. Section 2 Studying Matter and Energy Chapter 2

50. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Scientists Must Identify the Possible Variables, continued Variables that affect mileage might include: the use of a new brand of gasoline, driving more on highways, making fewer short trips, having the car’s engine serviced, and avoiding quick accelerations. To know if your hypothesis is right, the experiment must be designed to test each variable separately. Ideally, the experiments will eliminate all but one variable so that the exact cause can be identified. Section 2 Studying Matter and Energy Chapter 2

51. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Each Variable Must Be Tested Individually When a variable is kept constant from one experiment to the next, the variable is called a control. The procedure is called a controlled experiment. Think about how you might carry out a controlled experiment to test your hypothesis. First, you might fill the car with a new brand of gasoline and keep an accurate record of the mileage. Section 2 Studying Matter and Energy Chapter 2

52. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Each Variable Must Be Tested Individually, continued Then, you might fill the car with the old brand of gasoline and drive the car under the same conditions, again keeping record of the mileage. You then have designed the experiment so that only one variable—the brand of gasoline—is being tested. Section 2 Studying Matter and Energy Chapter 2

53. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Data from Experiments Can Lead to a Theory Any hypothesis that withstands repeated testing may become part of a theory. In science, a theory is a well-tested explanation of observations. (This is different from common use of the term, which means “a guess.”) Theories are explanations, not facts, so they can be disproved but can never be completely proven. Section 2 Studying Matter and Energy Chapter 2

54. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Theories and Laws Have Different Purposes Some facts in science always hold true. These facts are called laws. A law is a statement or mathematical expression that reliably describes a behavior of the natural world. While a theory is an attempt to explain the cause of certain events in the natural world, a scientific law describes the events. Section 2 Studying Matter and Energy Chapter 2

55. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Theories and Laws Visual Concepts Chapter 2 Click below to watch the Visual Concept. Visual Concept

56. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Theories and Laws Have Different Purposes, continued For example, the law of conservation of mass states that the products of a chemical reaction have the same mass as the reactants have. This law does not explain why matter in chemical reactions behaves this way; the law simply describes this behavior. Keep in mind that a hypothesis predicts an event, a theory explains it, and a law describes it. Section 2 Studying Matter and Energy Chapter 2

57. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Models Can Illustrate the Microscopic World of Chemistry A model represents an object, a system, a process, or an idea. A model is also simpler than the actual thing that is modeled. In chemistry, models can be most useful in understanding what is happening at the microscopic level. Section 2 Studying Matter and Energy Chapter 2

58. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Models Visual Concepts Chapter 2 Click below to watch the Visual Concept. Visual Concept

59. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Models Can Illustrate the Microscopic World of Chemistry, continued This model shows what happens during a reaction between a hydrogen molecule and an oxygen atom. Section 2 Studying Matter and Energy Chapter 2

60. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Explanations, continued Models Can Illustrate the Microscopic World of Chemistry, continued Keep in mind that models are simplified representations. For example, the actual particles of the chemical substances represented in the models do not have the shapes, sizes, or colors shown. These models do show the geometric arrangement of the units, their relative sizes, and how they interact. Section 2 Studying Matter and Energy Chapter 2

61. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer Divide a sheet of paper into three columns. In the first column, list measuring devices and instruments. In the second column, list what the devices in the first column measure. Finally, in the last column, list the units in which the devices report their measurements. Chapter 2 Section 3 Measurements and Calculations in Chemistry

62. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Distinguish between accuracy and precision in measurements. Determine the number of significant figures in a measurement, and apply rules for significant figures in calculations. Calculate changes in energy using the equation for specific heat, and round the results to the correct number of significant figures. Chapter 2 Section 3 Measurements and Calculations in Chemistry

63. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives, continued Write very large and very small numbers in scientific notation. Chapter 2 Section 3 Measurements and Calculations in Chemistry

64. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision To reduce the impact of error, scientists repeat their measurements and calculations many times. If their results are not consistent, they will try to identify and eliminate the source of error. Measurements Must Involve the Right Equipment Selecting the right equipment to make measurements is the first step to reducing errors in an experiment. For example, think about a beaker, a buret, and a graduated cylinder. Section 3 Measurements and Calculations in Chemistry Chapter 2

65. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision, continued Measurements Must Involve the Right Equipment, continued If an experimental procedure calls for measuring 8.6 mL of a liquid, you would use the buret. The buret allows you to measure a volume of liquid that is as close to 8.6 mL as possible. If a procedure calls for measuring 98 mL of a liquid, you would use a 100 mL graduated cylinder. Section 3 Measurements and Calculations in Chemistry Chapter 2

66. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision, continued Accuracy Is How Close a Measurement Is to the True Value When scientists make and report measurements, one factor they consider is accuracy. The accuracy of a measurement is how close the measurement is to the true or actual value. To understand what accuracy is, imagine that you throw four darts separately at a dartboard. Section 3 Measurements and Calculations in Chemistry Chapter 2

67. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision Section 3 Measurements and Calculations in Chemistry Chapter 2

68. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision, continued Accuracy Is How Close a Measurement Is to the True Value, continued Suppose the procedure for a chemical reaction calls for adding 36 mL of a solution. The experiment is done twice. The first time 35.8 mL is added, and the second time 37.2 mL is added. The first measurement was more accurate because 35.8 mL is closer to the true value of 36 mL. Section 3 Measurements and Calculations in Chemistry Chapter 2

69. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Accuracy and Precision, continued Precision Is How Closely Several Measurements Agree Another factor that scientists consider when making measurements is precision. Precision is the exactness of a measurement. It refers to how closely several measurements of the same quantity made in the same way can agree. To understand how precision differs from accuracy, consider darts landing on a dartboard. Section 3 Measurements and Calculations in Chemistry Chapter 2

70. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Accuracy and Precision Chapter 2 Click below to watch the Visual Concept. Visual Concept

71. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures When you make measurements or perform calculations, the way you report a value tells about how you got it. Scientists report values using significant figures. The significant figures of a measurement or a calculation consist of all the digits known with certainty as well as one estimated, or uncertain, digit. The last digit or significant figure reported after a measurement is uncertain or estimated. Section 3 Measurements and Calculations in Chemistry Chapter 2

72. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Significant Figures Chapter 2 Click below to watch the Visual Concept. Visual Concept

73. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Significant Figures Are Essential to Reporting Results Reporting all measurements in an experiment to the correct number of significant figures is necessary to be sure the results are true. Imagine you are measuring temperature with a ther- mometer calibrated in one-tenth degree increments. For a reading of 36.5°C, the three digits in the value are all significant figures. The first two digits are known with certainty, while the last is estimated. Section 3 Measurements and Calculations in Chemistry Chapter 2

74. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Significant Figures Are Essential to Reporting Results, continued The thermometer on the left is calibrated in one-degree increments, while the one on the right is calibrated in one-tenth degree increments. Section 3 Measurements and Calculations in Chemistry Chapter 2

75. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Rules for Determining Significant Figures 1.Nonzero digits are always significant. 2.Zeros between nonzero digits are significant. 3.Zeros in front of nonzero digits are not significant. 4.Zeros both at the end of a number and to the right of a decimal point are significant. Section 3 Measurements and Calculations in Chemistry Chapter 2

76. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Rules for Determining Significant Figures, continued 5.Zeros both at the end of a number but to the left of a decimal point may not be significant. If a zero has not been measured or estimated, it is not significant. A decimal point placed after zeros indicates that the zeros are significant. Section 3 Measurements and Calculations in Chemistry Chapter 2

77. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Calculators Do Not Identify Significant Figures When you use a calculator to find a result, you must pay special attention to significant figures. A calculator does not round the result to the correct number of significant figures. To determine the number of significant figures in the answer, you must first find the number of significant figures in the values used to calculate the answer. Section 3 Measurements and Calculations in Chemistry Chapter 2

78. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Rules for Using Significant Figures in Calculations 1.With multiplication and division, the answer cannot have more significant figures than the measurement with the smallest number of significant figures. 2.With addition and subtraction, the result can be no more certain than the least certain number in the calculation. 3.If a calculation has both addition (or subtraction) and multiplication (or division), round after each operation. Section 3 Measurements and Calculations in Chemistry Chapter 2

79. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Exact Values Have Unlimited Significant Figures Some values have an unlimited number of significant figures. These exact values have no uncertainty. One type of exact value, a count value, is determined by counting, not by measuring. Another value that can have an unlimited number of significant figures is a conversion factor. Ignore both count values and conversion factors when determining the number of significant figures. Section 3 Measurements and Calculations in Chemistry Chapter 2

80. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Determining the Number of Significant Figures Sample Problem A A student heats 23.62 g of a solid and observes that its temperature increases from 21.6°C to 36.79°C. Calculate the temperature increase per gram of solid. Section 3 Measurements and Calculations in Chemistry Chapter 2

81. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sample Problem A Solution Calculate the increase in temperature by subtracting the initial temperature (21.6°C) from the final temperature (36.79°C). temperature increase = final temperature  initial temperature 36.79°C  21.6°C = 15.19°C = 15.2°C Determining the Number of Significant Figures Section 3 Measurements and Calculations in Chemistry Chapter 2

82. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Determining the Number of Significant Figures Sample Problem A Solution, continued Calculate the temperature increase per gram of solid by dividing the temperature increase by the mass of the solid (23.62 g). Section 3 Measurements and Calculations in Chemistry Chapter 2 The answer is rounded to three significant figures.

83. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Specific Heat Depends on Various Factors Recall that the specific heat is the quantity of energy that must be transferred as heat to raise the temperature of 1 g of a substance by 1 K. Specific heat depends on the nature of the material that is changing temperature, the mass of the material, and the size of the temperature change. For example, iron has a larger specific heat than silver. Therefore, more energy as heat can be transferred to iron than to silver. Section 3 Measurements and Calculations in Chemistry Chapter 2

84. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Significant Figures, continued Calculating the Specific Heat of a Substance Specific heats can be used to compare how different materials absorb energy as heat under the same conditions. The specific heat (c p ) of a substance at a given pressure (p) is calculated by the following formula: Section 3 Measurements and Calculations in Chemistry Chapter 2 Note that q is the energy transferred as heat, m is the mass of the substance, and ∆T is the difference between the initial and final temperatures.

85. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calculating Specific Heat Sample Problem B A 4.0 g sample of glass was heated from 274 K to 314 K and was found to absorb 32 J of energy as heat. Calculate the specific heat of this glass. Section 3 Measurements and Calculations in Chemistry Chapter 2

86. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calculating Specific Heat Sample Problem B Solution Determine ∆T by calculating the difference between the initial and final temperatures. Insert the values into the equation for calculating specific heat and calculate. Section 3 Measurements and Calculations in Chemistry Chapter 2

87. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Notation Very large and very small numbers are often written in scientific notation. A number in scientific notation has two parts. The first part is a number that is between 1 and 10. The second part consists of a power of 10. To write the first part of the number, move the decimal to the right or the left so that only one nonzero digit is to the left of the decimal. Section 3 Measurements and Calculations in Chemistry Chapter 2

88. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Notation, continued Write the second part of the value as an exponent. This part is determined by counting the number of decimal places the decimal point is moved. If the decimal is moved to the right, the exponent is negative. If the decimal is moved to the left, the exponent is positive. Section 3 Measurements and Calculations in Chemistry Chapter 2

89. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Visual Concepts Scientific Notation Chapter 2 Click below to watch the Visual Concept. Visual Concept

90. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Notation, continued Scientific Notation in Calculations 1.In scientific notation, exponents are count values. 2.In addition and subtraction problems, all values must have the same exponent before they can be added or subtracted. The result is the sum of the difference of the first factors multiplied by the same exponent of 10. 3.In multiplication problems, the first factors of the numbers are multiplied and the exponents of 10 are added. Section 3 Measurements and Calculations in Chemistry Chapter 2

91. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Notation, continued Scientific Notation in Calculations, continued 4.In division problems, the first factors of the numbers are divided and the exponent of 10 in the denominator is subtracted from the exponent of 10 in the numerator. Section 3 Measurements and Calculations in Chemistry Chapter 2

92. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Scientific Notation, continued Scientific Notation with Significant Figures 1.Use scientific notation to eliminate all place-holding zeros. 2.Move the decimal in an answer so that only one digit is to the left, and change the exponent accordingly. The final value must contain the correct number of significant figures. Section 3 Measurements and Calculations in Chemistry Chapter 2