Chapter 2 Section 1 Energy 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.

Chapter 2 Chapter 2 Energy and Change Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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 H2O. Only the physical state of the substance changed.

Energy and Change, continued Chapter 2 Section 1 Energy 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, H2O, is a different substance than the hydrogen, H2, and oxygen, O2.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Law of Conservation of Energy Chapter 2 Visual Concepts Law of Conservation of Energy

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Conservation of Energy in a Chemical Reaction Chapter 2 Section 1 Energy Conservation of Energy in a Chemical Reaction

Energy and Change, continued Chapter 2 Section 1 Energy 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.

Chapter 2 Section 1 Energy 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.

Chapter 2 Heat, continued Energy Can Be Released As Heat Section 1 Energy 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.

Chapter 2 Heat, continued Energy Can Be Released As Heat, continued Section 1 Energy 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.

Chapter 2 Heat, continued Energy Can Be Absorbed As Heat Section 1 Energy 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: 2NaHCO3  Na2CO3 + H2O + CO2

Chapter 2 Heat, continued Heat Is Different from Temperature Section 1 Energy 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.

Chapter 2 Heat, continued Section 1 Energy 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.

Chapter 2 Heat, continued Section 1 Energy 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.

t(°C) = T(K)  273.15 K T(K) = t(°C) + 273.15°C Chapter 2 Section 1 Energy 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 K T(K) = t(°C) + 273.15°C The symbols t and T represent temperatures in degrees Celsius and in kelvins, respectively.

Temperature and Temperature Scale Chapter 2 Visual Concepts Temperature and Temperature Scale

Chapter 2 Heat, continued Section 1 Energy 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.

Chapter 2 Heat, continued Section 1 Energy 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.

Chapter 2 Heat, continued Section 1 Energy 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.

Heating Curve for Water Chapter 2 Section 1 Energy Heating Curve for Water

Chapter 2 Heat, continued Section 1 Energy 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.

Chapter 2 Heat, continued Section 1 Energy 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/g•K). Metals tend to have low specific heats. Water has an extremely high specific heat.

Specific Heat Capacity Chapter 2 Visual Concepts Specific Heat Capacity

Understanding Concepts Chapter 2 Standardized Test Preparation Understanding Concepts 5. Use the concept of specific heat to analyze the following observation: two pieces of metal with exactly the same mass are placed on a surface in bright sunlight. The temperature of the first block increases by 3°C while the temperature of the second increases by 8°C. Answer: Because the temperatures of the objects differ under the same conditions, they must have different specific heats, so they are made of different metals.

Understanding Concepts Chapter 2 Standardized Test Preparation Understanding Concepts 6. Describe the scientific method.

Understanding Concepts Chapter 2 Standardized Test Preparation Understanding Concepts 6. Describe the scientific method. Answer: The scientific method is a series of steps followed to solve problems, including collecting data, formulating a hypothesis, testing a hypothesis, and stating conclusions.

Chapter 2 Reading Skills Standardized Test Preparation Read the passage below. Then answer the questions. Several tests are needed before a new drug is approved for treatment. First, laboratory tests show the drug may be effective, but it is not given to humans. Next, human subjects receive the drug to determine if it is effective and if it has harmful side effects. Later “double-blind” tests are performed, where some patients receive the drug and others receive something that looks the same without the drug. Neither patient nor researcher knows who receives the drug. The double-blind test avoids introducing bias into the results based on expectations of the drug’s effectiveness. After testing, results are published to allow other researchers to evaluate the process and review the conclusions. These reviewers are important because they can provide independent analysis of the conclusions.

Chapter 2 Reading Skills Standardized Test Preparation Reading Skills 7. Which of the following is a reason that it is important that scientific results be confirmed by independent researchers? A. to introduce bias into expected results B. to obtain additional research funding C. to verify results are reproducible when conditions are duplicated D. to introduce changes into the experiment and determine whether the result changes

Chapter 2 Reading Skills Standardized Test Preparation Reading Skills 7. Which of the following is a reason that it is important that scientific results be confirmed by independent researchers? A. to introduce bias into expected results B. to obtain additional research funding C. to verify results are reproducible when conditions are duplicated D. to introduce changes into the experiment and determine whether the result changes

Chapter 2 Reading Skills Standardized Test Preparation Reading Skills 8. Why is it necessary for the investigator to accurately report experimental conditions? F. to guarantee that the right person receives credit for the discovery G. to show that researchers knew how to follow the scientific process H. to prove that the experiment was actually performed and not made up I. to allow other scientists to reproduce the experiment and confirm the observations

Chapter 2 Reading Skills Standardized Test Preparation Reading Skills 8. Why is it necessary for the investigator to accurately report experimental conditions? F. to guarantee that the right person receives credit for the discovery G. to show that researchers knew how to follow the scientific process H. to prove that the experiment was actually performed and not made up I. to allow other scientists to reproduce the experiment and confirm the observations

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics Use the graph below to answer questions 9–12.

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 9. What is happening during the portion of the graph labeled Heat of Vaporization, in which temperature does not change? A. No energy is added to the water. B. Added energy causes water molecules to move closer together. C. Added energy causes the water molecules to move farther apart. D. Added energy causes the water molecules to change from the solid state to the gas state.

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 9. What is happening during the portion of the graph labeled Heat of Vaporization, in which temperature does not change? A. No energy is added to the water. B. Added energy causes water molecules to move closer together. C. Added energy causes the water molecules to move farther apart. D. Added energy causes the water molecules to change from the solid state to the gas state.

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 10. For a given mass of water, which of these processes requires the greatest addition of energy for a 1°C temperature change F. heating a gas G. heating a solid H. heating a liquid I. changing a solid to a liquid

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 10. For a given mass of water, which of these processes requires the greatest addition of energy for a 1°C temperature change F. heating a gas G. heating a solid H. heating a liquid I. changing a solid to a liquid

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 11. How does the temperature change between the beginning of vaporization and the end of vaporization of water? A. temperature decreases slowly B. temperature does not change C. temperature increases slowly D. temperature increases rapidly

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 11. How does the temperature change between the beginning of vaporization and the end of vaporization of water? A. temperature decreases slowly B. temperature does not change C. temperature increases slowly D. temperature increases rapidly

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 12. On what portion of this graph are water molecules separated by the greatest distance?

Interpreting Graphics Chapter 2 Standardized Test Preparation Interpreting Graphics 12. On what portion of this graph are water molecules separated by the greatest distance? Answer: The right side of the graph, which shows the conditions of water in the gas phase.