Introductory Chemistry, 3rd Edition Nivaldo Tro

Introductory Chemistry, 3rd Edition Nivaldo Tro
Chapter 3 Matter and Energy Basic Principles of Chemistry Online Southeast Missouri State University Cape Girardeau, MO 2009, Prentice Hall

Tro's "Introductory Chemistry", Chapter 3
In Your Room Everything you can see, touch, smell or taste in your room is made of matter. Chemists study the differences in matter and how that relates to the structure of matter. Tro's "Introductory Chemistry", Chapter 3

What Is Matter? Matter is defined as anything that occupies space and has mass. Even though it appears to be smooth and continuous, matter is actually composed of a lot of tiny little pieces we call atoms and molecules. Tro's "Introductory Chemistry", Chapter 3

Atoms and Molecules Atoms are the tiny particles that make up all matter. In most substances, the atoms are joined together in units called molecules. The atoms are joined in specific geometric arrangements. Tro's "Introductory Chemistry", Chapter 3

Structure Determines Properties
The properties of matter are determined by the atoms and molecules that compose it. Composed of one carbon atom and one oxygen atom. Colorless, odorless gas. Burns with a blue flame. Binds to hemoglobin. Carbon Monoxide Composed of one carbon atom and two oxygen atoms. Colorless, odorless gas. Incombustible. Does not bind to hemoglobin. Carbon Dioxide

Classifying Matter by Physical State
Matter can be classified as solid, liquid, or gas based on what properties it exhibits. Fixed = Property doesn’t change when placed in a container. Indefinite = Takes the property of the container. Tro's "Introductory Chemistry", Chapter 3

Structure Determines Properties
The atoms or molecules have different structures in solids, liquids, and gases − leading to different properties.

Solids The particles in a solid are packed close together and are fixed in position. Although they may vibrate. The close packing of the particles results in solids being incompressible. The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container and prevents the particles from flowing. Tro's "Introductory Chemistry", Chapter 3

Solids, Continued Some solids have their particles arranged in an orderly geometric pattern—we call these crystalline solids. Salt and diamonds. Other solids have particles that do not show a regular geometric pattern over a long range—we call these amorphous solids. Plastic and glass. Tro's "Introductory Chemistry", Chapter 3

Liquids The particles in a liquid are closely packed, but they have some ability to move around. The close packing results in liquids being incompressible. The ability of the particles to move allows liquids to take the shape of their container and to flow. However, they don’t have enough freedom to escape and expand to fill the container. Tro's "Introductory Chemistry", Chapter 3

Gases In the gas state, the particles have complete freedom from each other. The particles are constantly flying around, bumping into each other and the container. In the gas state, there is a lot of empty space between the particles. On average. Tro's "Introductory Chemistry", Chapter 3

Gases, Continued Because there is a lot of empty space, the particles can be squeezed closer together. Therefore, gases are compressible. Because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container, and will flow. Tro's "Introductory Chemistry", Chapter 3

Classification of Matter by Appearance
Homogeneous = Matter that is uniform throughout. Appears to be one thing. Every piece of a sample has identical properties, though another sample with the same components may have different properties. Solutions (homogeneous mixtures) and pure substances. Heterogeneous = Matter that is non-uniform throughout . Contains regions with different properties than other regions. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Homogeneous or Heterogeneous
Table sugar. A mixture of table sugar and black pepper. A mixture of sugar dissolved in water. Oil and vinegar salad dressing. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Homogeneous or Heterogeneous, Continued Table sugar = homogeneous A mixture of table sugar and black pepper = heterogeneous A mixture of sugar dissolved in water = homogeneous Oil and vinegar salad dressing = heterogeneous Tro's "Introductory Chemistry", Chapter 3

Classifying Matter by Composition
Matter that is composed of only one kind of atom or molecule is called a pure substance. Matter that is composed of different kinds of atoms or molecules is called a mixture. Because pure substances always have only one kind of piece, all samples show the same properties. However, because mixtures have variable composition, different samples will show different properties. Tro's "Introductory Chemistry", Chapter 3

Copper—A Pure Substance
Color is brownish red. Shiny, malleable, and ductile. Excellent conductor of heat and electricity. Melting point = °C Density = 8.96 g/cm3 at 20 °C Tro's "Introductory Chemistry", Chapter 3

musical instruments and clock dials
Brass—A Mixture Type Color % Cu % Zn Density g/cm3 MP °C Tensile Strength psi Uses Gilding reddish 95 5 8.86 1066 50K pre-83 pennies, munitions, and plaques Commercial bronze 90 10 8.80 1043 61K door knobs and grillwork Jewelry 87.5 12.5 8.78 1035 66K costume jewelry Red golden 85 15 8.75 1027 70K electrical sockets, fasteners, and eyelets Low deep yellow 80 20 8.67 999 74K musical instruments and clock dials Cartridge yellow 70 30 8.47 954 76K car radiator cores Common 67 33 8.42 940 lamp fixtures and bead chain Muntz metal 60 40 8.39 904 nuts and bolts

Classification of Matter
Pure Substance Constant Composition Homogeneous Mixture Variable Composition Matter Pure Substance = All samples are made of the same pieces in the same percentages. Salt Mixtures = Different samples may have the same pieces in different percentages. Salt water Tro's "Introductory Chemistry", Chapter 3

Pure Substances vs. Mixtures
1. All samples have the same physical and chemical properties. 2. Constant composition = All samples have the same pieces in the same percentages. 3. Homogeneous. 4. Separate into components based on chemical properties. 5. Temperature stays constant while melting or boiling. Mixtures 1. Different samples may show different properties. 2. Variable composition = Samples made with the same pure substances may have different percentages. 3. Homogeneous or heterogeneous. 4. Separate into components based on physical properties. 5. Temperature usually changes while melting or boiling because composition changes. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Pure Substances or Mixtures
A homogeneous liquid whose temperature stays constant while boiling. Granite—a rock with several visible minerals in it. A red solid that turns blue when heated and releases water that is always 30% of the solid’s mass. A gas that when cooled and compressed, a liquid condenses out but some gas remains. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Pure Substances or Mixtures, Continued A homogeneous liquid whose temperature stays constant while boiling = pure substance. Granite—a rock with several visible minerals in it = mixture. A red solid that turns blue when heated and releases water that is always 30% of the solid’s mass = pure substance. A gas that when cooled and compressed, a liquid condenses out but some gas remains = mixture. Tro's "Introductory Chemistry", Chapter 3

Classification of Pure Substances
Substances that cannot be broken down into simpler substances by chemical reactions are called elements. Basic building blocks of matter. Composed of single type of atom. Although those atoms may or may not be combined into molecules. Substances that can be decomposed are called compounds. Chemical combinations of elements. Although properties of the compound are unrelated to the properties of the elements in it! Composed of molecules that contain two or more different kinds of atoms. All molecules of a compound are identical, so all samples of a compound behave the same way. Most natural pure substances are compounds. Tro's "Introductory Chemistry", Chapter 3

Atoms and Molecules Atoms Are submicroscopic particles that are the unit pieces of elements. Are the fundamental building blocks of all matter. Molecules Are submicroscopic particles that are the unit pieces of compounds. Two or more atoms attached together. Attachments are called bonds. Attachments come in different strengths. Molecules come in different shapes and patterns. Tro's "Introductory Chemistry", Chapter 3

Classification of Pure Substances
Elements Compounds 1. Made of one type of atom. (Some elements are found as multi-atom molecules in nature.) 2. Combine together to make compounds. 1. Made of one type of molecule, or array of ions. 2. Molecules contain 2 or more different kinds of atoms. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Elements or Compounds
Chlorine, Cl2 Table sugar, C12H22O11 A red solid that turns blue when heated and releases water that is always 30% of the solid’s mass. A brown-red liquid that, when energy is applied to it in any form, causes only physical changes in the material, not chemical. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify the Following as Elements or Compounds, Continued
Chlorine, Cl2 = element. Table sugar, C12H22O11 = compound. A red solid that turns blue when heated and releases water that is always 30% of the solid’s mass = compound. A brown-red liquid that, when energy is applied to it in any form, causes only physical changes in the material, not chemical = element. Tro's "Introductory Chemistry", Chapter 3

Classification of Mixtures
Mixtures are generally classified based on their uniformity. Mixtures that are uniform throughout are called homogeneous. Also known as solutions. Mixing is on the molecular level. Mixtures that have regions with different characteristics are called heterogeneous. Tro's "Introductory Chemistry", Chapter 3

Classification of Mixtures, Continued
Heterogeneous Homogeneous 1. Made of multiple substances, whose presence can be seen. 2. Portions of a sample have different composition and properties. 1. Made of multiple substances, but appears to be one substance. 2. All portions of a sample have the same composition and properties. Tro's "Introductory Chemistry", Chapter 3

Classifying Matter

Properties Distinguish Matter
Each sample of matter is distinguished by its characteristics. The characteristics of a substance are called its properties. Some properties of matter can be observed directly. Other properties of matter are observed when it changes its composition. Tro's "Introductory Chemistry", Chapter 3

Properties of Matter Physical Properties are the characteristics of matter that can be changed without changing its composition. Characteristics that are directly observable. Chemical Properties are the characteristics that determine how the composition of matter changes as a result of contact with other matter or the influence of energy. Characteristics that describe the behavior of matter. Tro's "Introductory Chemistry", Chapter 3

Some Physical Properties
Tro's "Introductory Chemistry", Chapter 3

Some Physical Properties of Iron
Iron is a silvery solid at room temperature with a metallic taste and smooth texture. Iron melts at 1538 °C and boils at 4428 °C. Iron’s density is 7.87 g/cm3. Iron can be magnetized. Iron conducts electricity, but not as well as most other common metals. Iron’s ductility and thermal conductivity are about average for a metal. It requires 0.45 J of heat energy to raise the temperature of one gram of iron by 1°C. Tro's "Introductory Chemistry", Chapter 3

Some Chemical Properties

Some Chemical Properties of Iron
Iron is easily oxidized in moist air to form rust. When iron is added to hydrochloric acid, it produces a solution of ferric chloride and hydrogen gas. Iron is more reactive than silver, but less reactive than magnesium. Tro's "Introductory Chemistry", Chapter 3

Practice—Decide Whether Each of the Observations About Table Salt Is a Physical or Chemical Property Salt is a white, granular solid. Salt melts at 801 °C. Salt is stable at room temperature, it does not decompose. 36 g of salt will dissolve in 100 g of water. Salt solutions and molten salt conduct electricity. When a clear, colorless solution of silver nitrate is added to a salt solution, a white solid forms. When electricity is passed through molten salt, a gray metal forms at one terminal and a yellow-green gas at the other. Tro's "Introductory Chemistry", Chapter 3

Practice − Decide Whether Each of the Observations About Table Salt Is a Physical or Chemical Property Salt is a white, granular solid = physical. Salt melts at 801 °C = physical. Salt is stable at room temperature, it does not decompose = chemical. 36 g of salt will dissolve in 100 g of water = physical. Salt solutions and molten salt conduct electricity = physical. When a clear, colorless solution of silver nitrate is added to a salt solution, a white solid forms = chemical. When electricity is passed through molten salt, a gray metal forms at one terminal and a yellow-green gas at the other = chemical. Tro's "Introductory Chemistry", Chapter 3

Changes in Matter Changes that alter the state or appearance of the matter without altering the composition are called physical changes. Changes that alter the composition of the matter are called chemical changes. During the chemical change, the atoms that are present rearrange into new molecules, but all of the original atoms are still present. Tro's "Introductory Chemistry", Chapter 3

Changes in Matter, Continued
Physical Changes—Changes in the properties of matter that do not effect its composition. Heating water. Raises its temperature, but it is still water. Evaporating butane from a lighter. Dissolving sugar in water. Even though the sugar seems to disappear, it can easily be separated back into sugar and water by evaporation. Tro's "Introductory Chemistry", Chapter 3

Changes in Matter, Continued
Chemical Changes involve a change in the properties of matter that change its composition. A chemical reaction. Rusting is iron combining with oxygen to make iron(III) oxide. Burning results in butane from a lighter to be changed into carbon dioxide and water. Silver combines with sulfur in the air to make tarnish. Tro's "Introductory Chemistry", Chapter 3

Is it a Physical or Chemical Change?
A physical change results in a different form of the same substance. The kinds of molecules don’t change. A chemical change results in one or more completely new substances. Also called chemical reactions. The new substances have different molecules than the original substances. You will observe different physical properties because the new substances have their own physical properties. Tro's "Introductory Chemistry", Chapter 3

Phase Changes Are Physical Changes
Boiling = liquid to gas. Melting = solid to liquid. Subliming = solid to gas. Freezing = liquid to solid. Condensing = gas to liquid. Deposition = gas to solid. State changes require heating or cooling the substance. Evaporation is not a simple phase change, it is a solution process. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify Each Change as Physical or Chemical
Evaporation of rubbing alcohol. Sugar turning black when heated. An egg splitting open and spilling out. Sugar fermenting. Bubbles escaping from soda. Bubbles that form when hydrogen peroxide is mixed with blood. Tro's "Introductory Chemistry", Chapter 3

Practice—Classify Each Change as Physical or Chemical, Continued
Evaporation of rubbing alcohol = physical. Sugar turning black when heated = chemical. An egg splitting open and spilling out = physical. Sugar fermenting = chemical. Bubbles escaping from soda = physical. Bubbles that form when hydrogen peroxide is mixed with blood = chemical. Tro's "Introductory Chemistry", Chapter 3

Separation of Mixtures
Separate mixtures based on different physical properties of the components. Physical change. Centrifugation and decanting Density Evaporation Volatility Chromatography Adherence to a surface Filtration State of matter (solid/liquid/gas) Distillation Boiling point Technique Different Physical Property Tro's "Introductory Chemistry", Chapter 3

Distillation Tro's "Introductory Chemistry", Chapter 3

Filtration Tro's "Introductory Chemistry", Chapter 3

Law of Conservation of Mass
Antoine Lavoisier “Matter is neither created nor destroyed in a chemical reaction.” The total amount of matter present before a chemical reaction is always the same as the total amount after. The total mass of all the reactants is equal to the total mass of all the products. Tro's "Introductory Chemistry", Chapter 3

Conservation of Mass Total amount of matter remains constant in a chemical reaction. 58 grams of butane burns in 208 grams of oxygen to form 176 grams of carbon dioxide and 90 grams of water. butane oxygen  carbon dioxide + water 58 grams grams  grams grams 266 grams = grams Tro's "Introductory Chemistry", Chapter 3

Practice—A Student Places Table Sugar and Sulfuric Acid into a Beaker and Gets a Total Mass of g. Shortly, a Reaction Starts that Produces a “Snake” of Carbon Extending from the Beaker and Steam Is Seen Escaping. If the Carbon Snake and Beaker at the End Have a Total Mass of g, How Much Steam Was Produced? Tro's "Introductory Chemistry", Chapter 3

Practice—A Student Places Table Sugar and Sulfuric Acid into a Beaker and Gets a Total Mass of g. Shortly, a Reaction Starts that Produces a “Snake” of Carbon Extending from the Beaker and Steam Is Seen Escaping. If the Carbon Snake and Beaker at the End Have a Total Mass of g, How Much Steam Was Produced? Total of reactants and beaker = g. Conservation of mass says total of products and beaker must be g. Mass of steam = g − g = 14.4 g. Tro's "Introductory Chemistry", Chapter 3

Energy There are things that do not have mass and volume. These things fall into a category we call energy. Energy is anything that has the capacity to do work. Although chemistry is the study of matter, matter is effected by energy. It can cause physical and/or chemical changes in matter. Tro's "Introductory Chemistry", Chapter 3

Law of Conservation of Energy
“Energy can neither be created nor destroyed.” The total amount of energy in the universe is constant. There is no process that can increase or decrease that amount. However, we can transfer energy from one place in the universe to another, and we can change its form. Tro's "Introductory Chemistry", Chapter 3

Matter Possesses Energy
When a piece of matter possesses energy, it can give some or all of it to another object. It can do work on the other object. All chemical and physical changes result in the matter changing energy. Tro's "Introductory Chemistry", Chapter 3

Kinds of Energy Kinetic and Potential
Potential energy is energy that is stored. Water flows because gravity pulls it downstream. However, the dam won’t allow it to move, so it has to store that energy. Kinetic energy is energy of motion, or energy that is being transferred from one object to another. When the water flows over the dam, some of its potential energy is converted to kinetic energy of motion. Tro's "Introductory Chemistry", Chapter 3

Some Forms of Energy Electrical Kinetic energy associated with the flow of electrical charge. Heat or Thermal Energy Kinetic energy associated with molecular motion. Light or Radiant Energy Kinetic energy associated with energy transitions in an atom. Nuclear Potential energy in the nucleus of atoms. Chemical Potential energy in the attachment of atoms or because of their position. Tro's "Introductory Chemistry", Chapter 3

Converting Forms of Energy
When water flows over the dam, some of its potential energy is converted to kinetic energy. Some of the energy is stored in the water because it is at a higher elevation than the surroundings. The movement of the water is kinetic energy. Along the way, some of that energy can be used to push a turbine to generate electricity. Electricity is one form of kinetic energy. The electricity can then be used in your home. For example, you can use it to heat cake batter you mixed, causing it to change chemically and storing some of the energy in the new molecules that are made. Tro's "Introductory Chemistry", Chapter 3

Using Energy We use energy to accomplish all kinds of processes, but according to the Law of Conservation of Energy we don’t really use it up! When we use energy we are changing it from one form to another. For example, converting the chemical energy in gasoline into mechanical energy to make your car move. Tro's "Introductory Chemistry", Chapter 3

“Losing” Energy If a process was 100% efficient, we could theoretically get all the energy transformed into a useful form. Unfortunately we cannot get a 100% efficient process. The energy “lost” in the process is energy transformed into a form we cannot use. Tro's "Introductory Chemistry", Chapter 3

There’s No Such Thing as a Free Ride
When you drive your car, some of the chemical potential energy stored in the gasoline is released. Most of the energy released in the combustion of gasoline is transformed into sound or heat energy that adds energy to the air rather than move your car down the road. Tro's "Introductory Chemistry", Chapter 3

Units of Energy Calorie (cal) is the amount of energy needed to raise one gram of water by 1 °C. kcal = energy needed to raise 1000 g of water 1 °C. food calories = kcals. Energy Conversion Factors 1 calorie (cal) = 4.184 joules (J) 1 Calorie (Cal) 1000 calories (cal) 1 kilowatt-hour (kWh) 3.60 x 106 joules (J) Tro's "Introductory Chemistry", Chapter 3

Energy Use Unit Energy Required to Raise Temperature of 1 g of Water by 1°C Energy Required to Light 100-W Bulb for 1 Hour Energy Used by Average U.S. Citizen in 1 Day joule (J) 4.18 3.6 x 105 9.0 x 108 calorie (cal) 1.00 8.60 x 104 2.2 x 108 Calorie (Cal) 1.00 x 10-3 86.0 2.2 x 105 kWh 1.1 x 10-6 0.100 2.50 x 102 Tro's "Introductory Chemistry", Chapter 3

Example 3.5—Convert 225 Cal to Joules
Write down the Given quantity and its unit. Given: 225 Cal 3 sig figs Write down the quantity you want to Find and unit. Find: ? J Write down the appropriate Conversion Factors. Conversion Factors: 1 Cal = 1000 cal 1 cal = J Write a Solution Map. Solution Map: Cal cal J Follow the solution map to Solve the problem. Solution: Significant figures and round. Round: 225 Cal = 9.41 x 105 J 3 significant figures Check. Check: Units and magnitude are correct.

Example 3.5: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Write down the given quantity and its units. Given: 225 Cal Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Information Given: 225 Cal Write down the quantity to find and/or its units. Find: ? joules Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Information Given: 225 Cal Find: ? J Collect needed conversion factors: 1000 cal = 1 Cal 4.184 J = 1 cal Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Information Given: 225 Cal Find: ? J Conversion Factors: 1000 cal = 1 Cal; J = 1 cal Write a solution map for converting the units: Cal cal J Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Information Given: 225 Cal Find: ? J Conversion Factors: 1000 cal = 1 Cal; J = 1 cal Solution Map: Cal  cal  J Apply the solution map: = J Significant figures and round: = 9.41 x 105 J Tro's "Introductory Chemistry", Chapter 3

Example: A candy bar contains 225 Cal of nutritional energy
Example: A candy bar contains 225 Cal of nutritional energy. How many joules does it contain? Information Given: 225 Cal Find: ? J Conversion Factors: 1000 cal = 1 Cal; J = 1 cal Solution Map: Cal  cal  J Check the solution: 225 Cal = 9.41 x 105 J The units of the answer, J, are correct. The magnitude of the answer makes sense since joules are much smaller than Cals. Tro's "Introductory Chemistry", Chapter 3

Chemical Potential Energy
The amount of energy stored in a material is its chemical potential energy. The stored energy arises mainly from the attachments between atoms in the molecules and the attractive forces between molecules. When materials undergo a physical change, the attractions between molecules change as their position changes, resulting in a change in the amount of chemical potential energy. When materials undergo a chemical change, the structures of the molecules change, resulting in a change in the amount of chemical potential energy. Tro's "Introductory Chemistry", Chapter 3

Energy Changes and Chemical Reactions
Chemical reactions happen most readily when energy is released during the reaction. Molecules with lots of chemical potential energy are less stable than ones with less chemical potential energy. Energy will be released when the reactants have more chemical potential energy than the products. Tro's "Introductory Chemistry", Chapter 3

Exothermic Processes When a change results in the release of energy it is called an exothermic process. An exothermic chemical reaction occurs when the reactants have more chemical potential energy than the products. The excess energy is released into the surrounding materials, adding energy to them. Often the surrounding materials get hotter from the energy released by the reaction. Tro's "Introductory Chemistry", Chapter 3

An Exothermic Reaction
Surroundings reaction Potential energy Reactants Products Amount of energy released Tro's "Introductory Chemistry", Chapter 3

Endothermic Processes
When a change requires the absorption of energy it is called an endothermic process. An endothermic chemical reaction occurs when the products have more chemical potential energy than the reactants. The required energy is absorbed from the surrounding materials, taking energy from them. Often the surrounding materials get colder due to the energy being removed by the reaction. Tro's "Introductory Chemistry", Chapter 3

An Endothermic Reaction
Surroundings reaction Potential energy Products Reactants Amount of energy absorbed Tro's "Introductory Chemistry", Chapter 3

Temperature Scales Fahrenheit scale, °F. Used in the U.S. Celsius scale, °C. Used in all other countries. A Celsius degree is 1.8 times larger than a Fahrenheit degree. Kelvin scale, K. Absolute scale. Tro's "Introductory Chemistry", Chapter 3

Temperature Scales Celsius Kelvin Fahrenheit Rankine 100°C 373 K 212°F
Boiling point water 298 K 75°F 534 R Room temp 25°C 0°C 273 K 32°F 459 R Melting point ice -38.9°C 234.1 K -38°F 421 R Boiling point mercury -183°C 90 K -297°F 162 R Boiling point oxygen BP helium -269°C 4 K -452°F 7 R -273°C 0 K -459 °F 0 R Absolute zero Celsius Kelvin Fahrenheit Rankine

Temperature Scales The Fahrenheit temperature scale used as its two reference points the freezing point of concentrated saltwater (0 °F) and average body temperature (96 °F). More accurate measure now sets average body temperature at 98.6 °F. Room temperature is about 72 °F. Tro's "Introductory Chemistry", Chapter 3

Temperature Scales, Continued
The Celsius temperature scale used as its two reference points the freezing point of distilled water (0 °C) and boiling point of distilled water (100 °C). More reproducible standards. Most commonly used in science. Room temperature is about 22 °C. Tro's "Introductory Chemistry", Chapter 3

Fahrenheit vs. Celsius A Celsius degree is 1.8 times larger than a Fahrenheit degree. The standard used for 0° on the Fahrenheit scale is a lower temperature than the standard used for 0° on the Celsius scale. Tro's "Introductory Chemistry", Chapter 3

The Kelvin Temperature Scale
Both the Celsius and Fahrenheit scales have negative numbers. Yet, real physical things are always positive amounts! The Kelvin scale is an absolute scale, meaning it measures the actual temperature of an object. 0 K is called absolute zero. It is too cold for matter to exist because all molecular motion would stop. 0 K = -273 °C = -459 °F. Absolute zero is a theoretical value obtained by following patterns mathematically. Tro's "Introductory Chemistry", Chapter 3

Kelvin vs. Celsius The size of a “degree” on the Kelvin scale is the same as on the Celsius scale. Although technically, we don’t call the divisions on the Kelvin scale degrees; we call them kelvins! That makes 1 K 1.8 times larger than 1 °F. The 0 standard on the Kelvin scale is a much lower temperature than on the Celsius scale. When converting between kelvins and °C, remember that the kelvin temperature is always the larger number and always positive! Tro's "Introductory Chemistry", Chapter 3

Example 3.7—Convert –25 °C to Kelvins
Write down the Given quantity and its unit. Given: -25 °C units place Write down the quantity you want to Find and unit. Find: K Write down the appropriate Equations. Equation: K = ° C + 273 Write a Solution Map. Solution Map: ° C K Follow the solution map to Solve the problem. Solution: Significant figures and round. Round: 258 K units place Units and magnitude are correct. Check. Check:

Example 3.8—Convert 55° F to Celsius
Write down the Given quantity and its unit. Given: 55 °F units place and 2 sig figs Write down the quantity you want to Find and unit. Find: ° C Write down the appropriate Equations. Equation: Write a Solution Map. Solution Map: ° F ° C Follow the solution map to Solve the problem. Solution: Significant figures and round. Round: °C = 13 °C units place and 2 sig figs Check. Check: Units and magnitude are correct.

Example 3.9—Convert 310 K to Fahrenheit
Write down the Given quantity and its unit. Given: 310 K units place and 3 sig figs Write down the quantity you want to Find and unit. Find: °F Write down the appropriate Equations. Equation: K = °C + 273 Write a Solution Map. Solution Map: °F °C K °C = K - 273 Follow the solution map to Solve the problem. Solution: Significant figures and round. Round: 98.6 °F = 99 °F units place and 2 sig figs Check. Check: Units and magnitude are correct.

Example 3.9: Convert 310 K to Fahrenheit. Tro's "Introductory Chemistry", Chapter 3

Example: Convert 310 K to Fahrenheit.
Write down the given quantity and its units. Given: 310 K Tro's "Introductory Chemistry", Chapter 3

Information Given: 310 K Write down the quantity to find and/or its units. Find: ? °F Tro's "Introductory Chemistry", Chapter 3

Information Given: 310 K Find: ? °F Collect needed equations: Tro's "Introductory Chemistry", Chapter 3

Information Given: 310 K Find: ? °F Equations: Write a solution map: K °C °F Tro's "Introductory Chemistry", Chapter 3

Information Given: 310 K Find: ? °F Equations: Solution Map: K  °C  °F Apply the solution map: Significant figures and round: = 99 °F Tro's "Introductory Chemistry", Chapter 3

Information Given: 310 K Find: ? °F Equations: Solution Map: K  °C  °F Check the solution: 310 K = 99 °F The units of the answer, °F, are correct. The magnitude of the answer makes sense since both are above, but close to, room temperature. Tro's "Introductory Chemistry", Chapter 3

Practice—Convert 0 °F into Kelvin

Practice—Convert 0 °F into Kelvin, Continued
°C = 0.556(°F-32) °C = 0.556(0-32) °C = -18 °C K = °C + 273 K = (-18) + 273 K = 255 K Tro's "Introductory Chemistry", Chapter 3

Energy and the Temperature of Matter
The amount the temperature of an object increases depends on the amount of heat energy added (q). If you double the added heat energy the temperature will increase twice as much. The amount the temperature of an object increases depending on its mass. If you double the mass, it will take twice as much heat energy to raise the temperature the same amount. Tro's "Introductory Chemistry", Chapter 3

Heat Capacity Heat capacity is the amount of heat a substance must absorb to raise its temperature by 1 °C. cal/°C or J/°C. Metals have low heat capacities; insulators have high heat capacities. Specific heat = heat capacity of 1 gram of the substance. cal/g°C or J/g°C. Water’s specific heat = J/g°C for liquid. Or cal/g°C. It is less for ice and steam.

Specific Heat Capacity
Specific heat is the amount of energy required to raise the temperature of one gram of a substance by 1 °C. The larger a material’s specific heat is, the more energy it takes to raise its temperature a given amount. Like density, specific heat is a property of the type of matter. It doesn’t matter how much material you have. It can be used to identify the type of matter. Water’s high specific heat is the reason it is such a good cooling agent. It absorbs a lot of heat for a relatively small mass. Tro's "Introductory Chemistry", Chapter 3

Specific Heat Capacities

Heat Gain or Loss by an Object
The amount of heat energy gained or lost by an object depends on 3 factors: how much material there is, what the material is, and how much the temperature changed. Amount of Heat = Mass x Heat Capacity x Temperature Change q = m x C x DT Tro's "Introductory Chemistry", Chapter 3

Units and magnitude are correct.
Example 3.10—Calculate Amount of Heat Needed to Raise Temperature of 2.5 g Ga from 25.0 to 29.9 °C Write down the Given quantity and its unit. Given: m = 2.5 g, T1 = 25.0 °C, T2= 29.9 °C, C = J/g°C Write down the quantity you want to Find and unit. Find: q, J Write down the appropriate Equations. Equation: Write a Solution Map. Solution Map: m, C, DT q Follow the solution map to Solve the problem. Solution: Significant figures and round. Round: 4.557 J = 4.6 J 2 significant figures Units and magnitude are correct. Check. Check:

Example 3.10: Gallium is a solid metal at room temperature, but melts at 29.9 °C. If you hold gallium in your hand, it melts from body heat. How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Tro's "Introductory Chemistry", Chapter 3

Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Write down the given quantity and its units. Given: mass of Ga = 2.5 g starting temp. = 25.0 °C final temp. = 29.9 °C spec. heat of Ga = J/g°C Tro's "Introductory Chemistry", Chapter 3

Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Information Given: m = 2.5 g; Ti = 25.0 °C; Tf = 29.9 °C; C = J/g°C Write down the quantity to find and/or its units. Find: amount of heat in joules Tro's "Introductory Chemistry", Chapter 3

Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Information Given: m = 2.5 g; Ti = 25.0 °C; Tf = 29.9 °C; C = J/g°C Find: q (J) Collect needed equations: Tro's "Introductory Chemistry", Chapter 3

Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Information Given: m = 2.5 g; Ti = 25.0 °C; Tf = 29.9 °C; C = J/g°C Find: q (J) Equation: q = m ∙ C ∙ DT Write a solution map: C, m, DT q Tro's "Introductory Chemistry", Chapter 3

Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Information Given: m = 2.5 g; Ti = 25.0 °C; Tf = 29.9 °C; C = J/g°C Find: q (J) Equation: q = m ∙ C ∙ DT Solution Map: m, C, DT  q Apply the solution map: = J Significant figures and round: q = 4.6 J Tro's "Introductory Chemistry", Chapter 3

Check the solution: q = 4.6 J
Example: How much heat must 2.5 g of gallium absorb from your hand to raise its temperature from 25.0 °C to 29.9 °C? The heat capacity of gallium is J/g°C. Information Given: m = 2.5 g; Ti = 25.0 °C; Tf = 29.9 °C; C = J/g°C Find: q (J) Equation: q = m ∙ C ∙ DT Solution Map: m, C, DT  q Check the solution: q = 4.6 J The units of the answer, J, are correct. The magnitude of the answer makes sense since the temperature change, mass, and specific heat are small. Tro's "Introductory Chemistry", Chapter 3

Practice—Calculate the Amount of Heat Released When 7.40 g of Water Cools from 49° to 29 °C Tro's "Introductory Chemistry", Chapter 3

The unit and sign are correct.
Practice—Calculate the Amount of Heat Released When 7.40 g of Water Cools from 49° to 29 °C, Continued Sort Information Given: Find: T1 = 49 °C, T2 = 29 °C, m = 7.40 g q, J q = m ∙ Cs ∙ DT Cs = 4.18 J/gC (Table 3.4) Strategize Solution Map: Relationships: Cs m, DT q Follow the concept plan to solve the problem. Solution: Check. Check: The unit and sign are correct.

Introductory Chemistry, 3rd Edition Nivaldo Tro

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