Name Date Class THE FLOW OF ENERGY HEAT AND WORK

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1 17.1 THE FLOW OF ENERGY HEAT AND WORK Section Review Objectives Explain the relationship between energy, heat, and work Distinguish between exothermic and endothermic processes Distinguish between heat capacity and specific heat Vocabulary thermochemistry chemical potential energy heat system surroundings law of conservation of energy endothermic process exothermic process heat capacity specific heat Key Equations and Relationships 1 Calorie 1 kilocalorie 1000 calories 1 J cal and J 1 cal q C m T heat (joules or calories) mass (g) change in temperature ( C) Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The energy that flows from a warm object to a cool object 1. is called 1. The energy stored within the structural units of 2. chemical substances is called chemical 2. The study of heat 3. transfer during chemical reactions and changes of state is called One of the units used to measure heat flow is the 4, 5. defined as the amount of heat needed to raise 1 g of water 1 C. 6. The SI unit of heat and energy is the 5, which is equal to cal. The 6 of a substance is the amount of heat it 8. takes to change the temperature of 1 g of the substance 1 C. Substances like 7, with low heat capacities, take a shorter time to heat up than substances with high heat capacities, such as 8. Chapter 17 Thermochemistry 429

2 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 9. The joule is the SI unit of force. 10. Endothermic processes absorb heat from the surroundings. 11. The law of conservation of energy states that in a chemical process, energy is sometimes created and sometimes destroyed. 12. A system that loses heat to its surrounding is said to be exothermic, and the value of q is negative. 13. A calorie is defined as the quantity of heat needed to raise the temperature of 1 gram of pure water 1 C. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B heat exothermic process heat capacity a. a process that absorbs heat from the surroundings b. the amount of heat required to change the temperature of an object by exactly 1 C c. energy that transfers from one object to another because of a temperature difference between them system endothermic process Part D Questions and Problems d. the part of the universe being studied e. a process that loses heat to the surroundings Answer the following in the space provided. 19. Distinguish among the various forms of energy: chemical potential energy, work, and heat. 20. The temperature of a piece of unknown metal with a mass of 18.0 g increases from 25.0 C to 40 C when the metal absorbs J of heat. What is the specific heat of the unknown metal? Compare your answer to the values listed in Table 17.2 of your textbook. What is the identity of the unknown metal? 430 Core Teaching Resources

3 17.2 MEASURING AND EXPRESSING ENTHALPY CHANGES Section Review Objectives Construct equations that show the enthalpy changes for chemical and physical processes Calculate enthalpy changes in chemical and physical processes Vocabulary calorimetry calorimeter enthalpy, (H) thermochemical equation heat of reaction heat of combustion Key Equation q sys H q surr m C T, where T T f T i Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. A 1 is a device used to measure the absorption or 1. release of heat in chemical and physical processes. For systems at 2. constant pressure, the heat changes that occur are the same as 3. changes in 2, symbolized as 3. To measure the 4. enthalpy change for a reaction in aqueous solution, it is necessary 5. to measure the 4 and 5 temperatures of the system 6. and the Part B True-False of the water in the system. Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT When a substance dissolves in water, heat is released. 8. The sign of H is negative for an exothermic reaction. 9. If 129 kj of heat is required to decompose 2 moles of NaHCO 3, then 258 kj is required to decompose 4 moles of NaHCO 3. Chapter 17 Thermochemistry 431

4 10. The physical state of the reactants and products in a thermochemical reaction are not important when calculating H of the reaction. 11. In endothermic reactions, the potential energy of the product(s) is higher than the potential energy of the reactants. 12. The equation CaO(s) H 2 O(l) Ca(OH) 2 (s) H 65.2 kj is an example of a thermochemical equation. Part C Matching Match each description in Column B to the correct term in Column A Column A enthalpy (H) heat of combustion Column B a. the heat of reaction for the complete burning of 1 mole of a substance b. a chemical equation that includes the enthalpy change ( H) 15. thermochemical equation c. the accurate and precise measurement of heat changes for chemical and physical processes calorimetry bomb calorimeter Part D Questions and Problems d. an insulated device containing a sealed vessel that is used to measure the heat released during a combustion reaction e. the amount of heat that a system has at a constant pressure Answer the following in the space provided. 18. When 2 moles of nitric oxide, NO, burn in air to produce 2 moles of nitrogen dioxide, kj of heat is produced. Write a balanced thermochemical equation for this reaction. 19. Calculate the amount of heat produced when 34.8 g of methane, CH 4, burns in an excess of oxygen, according to the following equation. CH 4 (g) 2O 2 (g) CO 2 (g) 2H 2 O(l) H kj 432 Core Teaching Resources

5 17.3 HEAT IN CHANGES OF STATE Section Review Objectives Classify, by type, the enthalpy changes that occur during melting, freezing, boiling, and condensing Calculate the enthalpy changes that occur during melting, freezing, boiling, and condensing Explain what thermochemical changes can occur when a solution forms Vocabulary molar heat of fusion molar heat of solidification molar heat of vaporization molar heat of condensation molar heat of solution Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The heat absorbed by 1 mole of a substance in melting from 1. a solid to a liquid at a constant temperature is called the The heat lost when 1 mole of a liquid solidifies at a constant 3. temperature is called the 2. The quantity of heat absorbed 4. by a melting solid is 3 to the quantity of heat lost when the 5. liquid solidifies. The heat of fusion for methanol is When liquids absorb heat at their boiling points, they become 7. vapors. The amount of heat necessary to vaporize one mole of a given liquid is called its 5. 6 is the exact opposite of vaporization. The amount of heat released when one mole of vapor condenses is called its 7. Chapter 17 Thermochemistry 433

6 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 8. H fus H solid 9. Melting and vaporization are exothermic processes. 10. In order to convert 1 mole of H 2 O(l) to 1 mol of H 2 O(g), 40.7 kj must be supplied. 11. When ice melts, the temperature of the ice increases until the entire sample becomes liquid. 12. When ammonium nitrate dissolves in water, the solution gets cold. This is an example of an exothermic reaction. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B molar heat of fusion molar heat of solidification molar heat of vaporization a. the heat absorbed by 1 mole of a substance in melting from a solid to a liquid b. the amount of heat necessary to vaporize 1 mole of a liquid c. H cond H vap molar heat of solution Part D Questions and Problems Answer the following in the space provided. 18. State whether the following physical and chemical changes are endothermic or exothermic. a. melting d. fusion b. vaporization e. freezing c. condensation f. combustion d. the heat change caused by dissolution of 1 mole of substance e. the heat lost when 1 mole of a liquid solidifies at a constant temperature 19. How much heat is absorbed when 28.3 g of H 2 O(s) at 0 C is converted to liquid at 0 C? 20. How much heat is absorbed when 5.53 mol of NH 4 NO 3 solid is dissolved in water? ( H soln 25.7 kj/mol) 434 Core Teaching Resources

7 17.4 CALCULATING HEATS OF REACTION Section Review Objectives Apply Hess s law of heat summation to find enthalpy changes for chemical and physical processes Calculate enthalpy changes using standard heats of formation Vocabulary Hess s law of heat summation standard heat of formation Key Equation H 0 H f 0 (products) H f 0 (reactants) Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Hess s law of heat summation states that for a chemical 1. equation that can be written as the 1 of two or more steps, 2. the 2 change for the final equation equals the sum of the 3. enthalpy changes for the individual steps. Hess s law makes it 4. possible to measure the heat of a reaction 3. When a 5. reaction is reversed, the sign of H must be Sometimes it is hard to measure the heat for a reaction. In 7. such cases, the 5 is used to calculate heats of reaction 8. at standard conditions. The standard heat of formation of a 9. compound is the 6 in enthalpy that accompanies the 10. formation of 7 mole of a compound from its elements. The symbol used for standard heat of formation is 8. The standard heat of formation of a free element in its standard state is 9. The standard heat of reaction is determined by 10 the H f 0 of all the reactants from the H f 0 of all the products. Chapter 17 Thermochemistry 435

8 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 11. The standard heat of formation for a substance is determined at 100 C. 12. Hess s law of heat summation is not related to the law of conservation of energy. 13. When using Hess s law of heat summation, intermediate reactions are summed and terms are canceled, as in algebra, to arrive at a final equation. 14. The H f 0 for I 2 (g) is zero. 15. The H f 0 for H 2 O(l) and H 2 O(s) are the same. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B standard heat of formation Hess s law of heat summation a. symbol for the standard heat of formation b. the change in enthalpy that accompanies the formation of 1 mole of a compound from its elements H f 0 H 0 for Br 2 (g) Br 2 (l) zero Part D Questions and Problems Answer the following in the space provided. 21. Determine the heat of reaction for the following reaction. CuO(s) H 2 (g) Cu(s) H 2 O(g) Use the following thermochemical equations. 1) CuO(s) y Cu(s) 1 2 O 2 (g) H 155 kj 2) H 2 O(g) y H 2 (g) 1 2 O 2 (g) H 242 kj c. in going from a particular set of reactants to a particular set of products, the enthalpy change is the same whether the reaction takes place in one step or in a series of steps d kj e. H f 0 of Cl 2 (g) 22. Calculate the change in enthalpy for the following reaction using standard heats of formation. (Refer to Table 17.4 in your textbook.) Fe 2 O 3 (s) 3CO(g) 2Fe(s) 3CO 2 (g) 436 Core Teaching Resources