Exercises (Energy, and heat) 1. Define energy. How is work related to energy? 2. Give two units of energy and indicate which one is preferred. 3. Express the quantity of \(422 \mathrm{~J}\) in calories. 4. Express the quantity of \(3.225 \mathrm{~kJ}\) in calories. 5. Express the quantity \(55.69 \mathrm{cal}\) in joules. 6. Express the quantity \(965.33 \mathrm{kcal}\) in joules. 7. How does a Calorie differ from a calorie? 8. Express the quantity 965.33 Cal in joules. 9. What is the law of conservation of energy? 10. What does the word conserved mean as applied to the law of conservation of energy? Answers 1. Energy is the ability to do work. Work is a form of energy. 3. \(101 \mathrm{cal}\) 5. \(233.0 \mathrm{~J}\) 7. A Calorie is actually a kilocalorie, or 1,000 calories. 9. The total energy of an isolated system does not increase or decrease. Exercises (Work) 1. Give two definitions of work. 2. What is the sign on work when a sample of gas increases its volume? Explain why work has that sign. 3. What is the work when a gas expands from \(3.00 \mathrm{~L}\) to \(12.60 \mathrm{~L}\) against an external pressure of \(0.888 \mathrm{~atm}\) ? 4. What is the work when a gas expands from \(0.666 \mathrm{~L}\) to \(2.334 \mathrm{~L}\) against an external pressure of \(2.07 \mathrm{~atm} ?\) 5. What is the work when a gas contracts from \(3.45 \mathrm{~L}\) to \(0.97 \mathrm{~L}\) under an external pressure of 0.985 atm? 6. What is the work when a gas contracts from \(4.66 \mathrm{~L}\) to \(1.22 \mathrm{~L}\) under an external pressure of 3.97 atm? 7. Like work, the sign on heat can be positive or negative. What is happening to the total energy of a system if heat is positive? 8. Like work, the sign on heat can be positive or negative. What is happening to the total energy of a system if heat is negative? 9. What is the heat when \(55.6 \mathrm{~g}\) of \(\mathrm{Fe}\) increase temperature from \(25.6^{\circ} \mathrm{C}\) to \(177.9^{\circ} \mathrm{C}\) ? The heat capacity of Fe is in Table 7.1 "Specific Heats of Various Substances". 10. What is the heat when \(0.444 \mathrm{~g}\) of \(\mathrm{Au}\) increases temperature from \(17.8^{\circ} \mathrm{C}\) to \(222.5^{\circ} \mathrm{C}\) ? The heat capacity of Au is in Table 7.1 "Specific Heats of Various Substances". 11. What is the heat when \(245 \mathrm{~g}\) of \(\mathrm{H}_2 \mathrm{O}\) cool from \(355 \mathrm{~K}\) to \(298 \mathrm{~K}\) ? The heat capacity of \(\mathrm{H}_2 \mathrm{O}\) is in Table 7.1 "Specific Heats of Various Substances". 12. What is the heat when \(100.0 \mathrm{~g}\) of \(\mathrm{Mg}\) cool from \(725 \mathrm{~K}\) to \(552 \mathrm{~K}\) ? The heat capacity of \(\mathrm{Mg}\) is in Table 7.1 "Specific Heats of Various Substances". 13. It takes \(452 \mathrm{~J}\) of heat to raise the temperature of a \(36.8 \mathrm{~g}\) sample of a metal from \(22.9^{\circ} \mathrm{C}\) to \(98.2^{\circ} \mathrm{C}\). What is the heat capacity of the metal? 14. It takes \(2,267 \mathrm{~J}\) of heat to raise the temperature of a \(44.5 \mathrm{~g}\) sample of a metal from \(33.9^{\circ} \mathrm{C}\) to \(288.3^{\circ} \mathrm{C}\). What is the heat capacity of the metal? 15. An experimenter adds \(336 \mathrm{~J}\) of heat to a \(56.2 \mathrm{~g}\) sample of \(\mathrm{Hg}\). What is its change in temperature? The heat capacity of Hg is in Table 7.1 "Specific Heats of Various Substances". 16. To a \(0.444 \mathrm{~g}\) sample of \(\mathrm{H}_2 \mathrm{O}, 23.4 \mathrm{~J}\) of heat are added. What is its change in temperature? The heat capacity of \(\mathrm{H}_2 \mathrm{O}\) is in Table 7.1 "Specific Heats of Various Substances". 17. An unknown mass of \(\mathrm{Al}\) absorbs \(187.9 \mathrm{~J}\) of heat and increases its temperature from \(23.5^{\circ} \mathrm{C}\) to \(35.6^{\circ} \mathrm{C}\). What is the mass of the aluminum? How many moles of aluminum is this? 18. A sample of He goes from \(19.4^{\circ} \mathrm{C}\) to \(55.9^{\circ} \mathrm{C}\) when \(448 \mathrm{~J}\) of energy are added. What is the mass of the helium? How many moles of helium is this? Answers 1. Work is a force acting through a distance or a volume changing against some pressure. 3. \(-864 \mathrm{~J}\) 5. \(248 \mathrm{~J}\) 7. When heat is positive, the total energy of the system is increasing. 9. \(3.80 \times 10^3 \mathrm{~J}\) 11. \(-58,400 \mathrm{~J}\) 13. \(0.163 \mathrm{~J} / \mathrm{g} \cdot{ }^{\circ} \mathrm{C}\) 15. \(43.0^{\circ} \mathrm{C}\) 17. \(17.3 \mathrm{~g} ; 0.640 \mathrm{~mol}\) Exercises (Enthalpy) 1. Under what circumstances are } q \text { and } \Delta H \text { the same? } 2. Under what circumstances are \(q\) and \(\Delta H\) different? 3. Hydrogen gas and chlorine gas react to make hydrogen chloride gas with an accompanying enthalpy change of \(-184 \mathrm{~kJ}\). Write a properly balanced thermochemical equation for this process. 4. Propane \(\left(\mathrm{C}_3 \mathrm{H}_8\right)\) reacts with elemental oxygen gas to produce carbon dioxide and liquid water with an accompanying enthalpy change of \(-2,220 \mathrm{~kJ}\). Write a properly balanced thermochemical equation for this process. 5. Nitrogen gas reacts with oxygen gas to make \(\mathrm{NO}(\mathrm{g})\) while absorbing \(180 \mathrm{~kJ}\). Write a properly balanced thermochemical equation for this process. 6. Solid sodium reacts with chlorine gas to make solid sodium chloride while giving off \(772 \mathrm{~kJ}\). Write a properly balanced thermochemical equation for this process. 7. Hydrogen gas and chlorine gas react to make hydrogen chloride gas with an accompanying enthalpy change of \(-184 \mathrm{~kJ}\). Is this process endothermic or exothermic? 8. Propane \(\left(\mathrm{C}_3 \mathrm{H}_8\right)\) reacts with elemental oxygen gas to produce carbon dioxide while giving off \(2,220 \mathrm{~kJ}\) of energy. Is this process endothermic or exothermic? 9. Nitrogen gas reacts with oxygen gas to make \(\mathrm{NO}(\mathrm{g})\) while absorbing \(180 \mathrm{~kJ}\). Is this process exothermic or endothermic? 10. Sodium metal can react with nitrogen to make sodium azide \(\left(\mathrm{NaN}_3\right)\) with a \(\Delta H\) of \(21.72 \mathrm{~kJ}\). Is this process exothermic or endothermic? 11. Draw an energy level diagram for the chemical reaction in Exercise 8. 12. Draw an energy level diagram for the chemical reaction in Exercise 9. (See Figure 7.3 "Reaction Energy" for an example.) 13. In a \(250 \mathrm{~mL}\) solution, \(0.25 \mathrm{~mol}\) of \(\mathrm{KOH}(\mathrm{aq})\) and \(0.25 \mathrm{~mol}\) of \(\mathrm{HNO}_3(\mathrm{aq})\) are combined. The temperature of the solution increases from \(22.5^{\circ} \mathrm{C}\) to \(35.9^{\circ} \mathrm{C}\). Assume the solution has the same density and heat capacity of water. What is the heat of the reaction, and what is the \(\Delta H\) of the reaction on a molar basis? 14. In a \(600 \mathrm{~mL}\) solution, \(0.50 \mathrm{~mol}\) of \(\mathrm{Ca}(\mathrm{OH})_2(\mathrm{aq})\) and \(0.50 \mathrm{~mol}\) of \(\mathrm{H}_2 \mathrm{SO}_4(\mathrm{aq})\) are combined. The temperature of the solution increases by \(22.3^{\circ} \mathrm{C}\). What is the heat of the reaction, and what is the \(\Delta H\) of the reaction on a molar basis? Assume the solution has the same density and heat capacity of water. 15. To warm \(400.0 \mathrm{~g}\) of \(\mathrm{H}_2 \mathrm{O}, 0.050 \mathrm{~mol}\) of ethanol \(\left(\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}\right)\) is burned. The water warms from \(24.6^{\circ} \mathrm{C}\) to \(65.6^{\circ} \mathrm{C}\). What is the heat of the reaction, and what is the \(\Delta H\) of the reaction on a molar basis? 16.To warm \(100.0 \mathrm{~g}\) of \(\mathrm{H}_2 \mathrm{O}, 0.066 \mathrm{~mol}\) beeswax is burned. The water warms from \(21.4^{\circ} \mathrm{C}\) to \(25.5^{\circ} \mathrm{C}\). What is the heat of the reaction, and what is the \(\Delta H\) of the reaction on a molar basis? Answers 1. under conditions of constant pressure 3. \(\mathrm{H}_2(\mathrm{~g})+\mathrm{Cl}_2(\mathrm{~g}) \rightarrow 2 \mathrm{HCl}(\mathrm{g}) \Delta H=-184 \mathrm{~kJ}\) 5. \(\mathrm{N}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow 2 \mathrm{NO}(\mathrm{g}) \Delta H=180 \mathrm{~kJ}\) 7. exothermic 9. endothermic 13. heat of reaction \(=-14.0 \mathrm{~kJ} ; \Delta H=-56.0 \mathrm{~kJ} / \mathrm{mol}\) of reactants 15. heat of reaction \(=-68.6 \mathrm{~kJ} ; \Delta H=-1,370 \mathrm{~kJ} / \mathrm{mole}\) of ethanol Exercises (Hess's Law) 1. Define Hess's law. 2. What does Hess's law require us to do to the \(\Delta H\) of a thermochemical equation if we reverse the equation? 3. If the \(\Delta H\) for \(\quad \quad \quad \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \rightarrow \mathrm{C}_2 \mathrm{H}_6 \notag \) is \(-65.6 \mathrm{~kJ}\), what is the \(\Delta H\) for this reaction? \(\quad \quad \quad \mathrm{C}_2 \mathrm{H}_6 \rightarrow \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \notag \) 4. If the \(\Delta H\) for \(\quad \quad \quad 2 \mathrm{Na}+\mathrm{Cl}_2 \rightarrow 2 \mathrm{NaCl} \notag \) is \(-772 \mathrm{~kJ}\), what is the \(\Delta H\) for this reaction: \(\quad \quad \quad 2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na}+\mathrm{Cl}_2 \notag \) 5. If the \(\Delta H\) for \(\quad \quad \quad \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \rightarrow \mathrm{C}_2 \mathrm{H}_6 \notag \) is \(-65.6 \mathrm{~kJ}\), what is the \(\Delta H\) for this reaction? \(\quad \quad \quad 2 \mathrm{C}_2 \mathrm{H}_4+2 \mathrm{H}_2 \rightarrow 2 \mathrm{C}_2 \mathrm{H}_6 \notag \) 6. If the \(\Delta H\) for \(\quad \quad \quad 2 \mathrm{C}_2 \mathrm{H}_6+7 \mathrm{O}_2 \rightarrow 4 \mathrm{CO}_2+6 \mathrm{H}_2 \mathrm{O} \notag \) is \(-2,650 \mathrm{~kJ}\), what is the \(\Delta H\) for this reaction? \(\quad \quad \quad 6 \mathrm{C}_2 \mathrm{H}_6+21 \mathrm{O}_2 \rightarrow 12 \mathrm{CO}_2+18 \mathrm{H}_2 \mathrm{O} \notag \) 7. The \(\Delta H\) for \(\quad \quad \quad \mathrm{C}_2 \mathrm{H}_4+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \notag \) is \(-44 \mathrm{~kJ}\). What is the \(\Delta H\) for this reaction? \(\quad \quad \quad 2 \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \rightarrow 2 \mathrm{C}_2 \mathrm{H}_4+2 \mathrm{H}_2 \mathrm{O} \notag \) 8. The \(\Delta H\) for \(\quad \quad \quad \mathrm{N}_2+\mathrm{O}_2 \rightarrow 2 \mathrm{NO} \notag \) is \(181 \mathrm{~kJ}\). What is the \(\Delta H\) for this reaction? \(\quad \quad \quad \mathrm{NO} \rightarrow 1 / 2 \mathrm{~N}_2+1 / 2 \mathrm{O}_2 \notag \) 9. Determine the \(\Delta H\) for the reaction \(\quad \quad \quad \mathrm{Cu}+\mathrm{Cl}_2 \rightarrow \mathrm{CuCl}_2 \notag \) given these data: \(\quad \quad \quad 2 \mathrm{Cu}+\mathrm{Cl}_2 \rightarrow 2 \mathrm{CuCl} \Delta H=-274 \mathrm{~kJ}\) \(\quad \quad \quad2 \mathrm{CuCl}+\mathrm{Cl}_2 \rightarrow 2 \mathrm{CuCl}_2 \Delta H=-166 \mathrm{~kJ} \notag \) 10. Determine \(\Delta H\) for the reaction \(\quad \quad \quad 2 \mathrm{CH}_4 \rightarrow 2 \mathrm{H}_2+\mathrm{C}_2 \mathrm{H}_4 \notag \) given these data: \(\begin{array}{l} \quad \quad \quad \mathrm{CH}_4+2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O} \Delta H=-891 \mathrm{~kJ} \\ \quad \quad \quad \mathrm{C}_2 \mathrm{H}_4+3 \mathrm{O}_2 \rightarrow 2 \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O} \Delta H=-1,411 \mathrm{~kJ} \\ \quad \quad \quad 2 \mathrm{H}_2+\mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O} \Delta H=-571 \mathrm{~kJ}\end{array}\) 11. Determine \(\Delta H\) for the reaction \(\quad \quad \quad \mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3 \rightarrow \mathrm{Fe}_2 \mathrm{O}_3+3 \mathrm{SO}_3 \notag \) given these data: \( \begin{array}{l} \quad \quad \quad 4 \mathrm{Fe}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{Fe}_2 \mathrm{O}_3 \Delta H=-1,650 \mathrm{~kJ} \\ \quad \quad \quad 2 \mathrm{~S}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{SO}_3 \Delta H=-792 \mathrm{~kJ} \\ \quad \quad \quad 2 \mathrm{Fe}+3 \mathrm{~S} +6 \mathrm{O}_2 \rightarrow \mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3 \Delta H=-2,583 \mathrm{~kJ} \end{array} \notag \) 12. Determine \(\Delta H\) for the reaction \(\quad \quad \quad \mathrm{CaCO}_3 \rightarrow \mathrm{CaO}+\mathrm{CO}_2 \notag \) given these data: \( \begin{array}{l} \quad \quad \quad 2 \mathrm{Ca}+2 \mathrm{C}+3 \mathrm{O}_2 \rightarrow 2 \mathrm{CaCO}_3 \Delta H=-2,414 \mathrm{kJ}\\ \quad \quad \quad \mathrm{CO}_2 \rightarrow \mathrm{CO}_2 \Delta H=-393.5 \mathrm{~kJ} 2 \\ \quad \quad \quad \mathrm{Ca}+\mathrm{O}_2 \rightarrow 2 \mathrm{CaO} \Delta H=-1,270 \mathrm{~kJ} \end{array} \notag \) Answers 1. If chemical equations are combined, their energy changes are also combined. 3. \(\Delta H=65.6 \mathrm{~kJ}\) 5. \(\Delta H=-131.2 \mathrm{~kJ}\) 7. \(\Delta H=88 \mathrm{~kJ}\) 9. \(\Delta H=-220 \mathrm{~kJ}\) 11. \(\Delta H=570 \mathrm{~kJ}\) Exercises (Formation Reactions) 1. Define formation reaction and give an example. 2. Explain the importance of formation reactions in thermochemical equations. 3. Which of the following reactions is a formation reaction? If it is not a formation reaction, explain why. a. \(\mathrm{H}_2(\mathrm{~g})+\mathrm{S}(\mathrm{s}) \rightarrow \mathrm{H}_2 \mathrm{~S}(\mathrm{~g})\) b. \(2 \mathrm{HBr}(\mathrm{g})+\mathrm{Cl}_2(\mathrm{~g}) \rightarrow 2 \mathrm{HCl}(\mathrm{g})+\mathrm{Br}_2(\ell)\) 4. Which of the following reactions is a formation reaction? If it is not a formation reaction, explain why. a. \(\mathrm{Fe}(\mathrm{g})+1 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{FeO}(\mathrm{s})\) b. \(\mathrm{Hg}(\ell)+1 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{HgO}(\mathrm{s})\) 5. Which of the following reactions is a formation reaction? If it is not a formation reaction, explain why a. \(\mathrm{H}_2(\mathrm{~g})+\mathrm{S}(\mathrm{s})+2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{H}_2 \mathrm{SO}_4(\ell)\) b. \(\mathrm{C}_3 \mathrm{H}_8(\mathrm{~g})+5 \mathrm{O}_2(\mathrm{~g}) \rightarrow 3 \mathrm{CO}_2(\mathrm{~g})+4 \mathrm{H}_2 \mathrm{O}(\ell)\) 6. Which of the following reactions is a formation reaction? If it is not a formation reaction, explain why. a. \(\mathrm{Zn}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{ZnCl}_2(\mathrm{aq})+\mathrm{H}_2(\mathrm{~g})\) b. \(2 \mathrm{Na}(\mathrm{s})+\mathrm{C}(\mathrm{s})+3 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{Na}_2 \mathrm{CO}_3(\mathrm{~s})\) 7. Write a proper formation reaction for each substance. a. \(\mathrm{H}_3 \mathrm{PO}_4(\mathrm{~s})\) b. \(\mathrm{Na}_2 \mathrm{O}(\mathrm{s})\) c. \(\mathrm{C}_3 \mathrm{H}_7 \mathrm{OH}(\ell)\) 8. Write a proper formation reaction for each substance. a. \(\mathrm{N}_2 \mathrm{O}_5(\mathrm{~g})\) b. \(\mathrm{BaSO}_4(\mathrm{~s})\) c. \(\mathrm{Fe}(\mathrm{OH})_3(\mathrm{~s})\) 9.Write a proper formation reaction for each substance. a. \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(\mathrm{~s})\) b. \(\mathrm{Zn}\left(\mathrm{NO}_3\right)_2(\mathrm{~s})\) c. \(\mathrm{Al}(\mathrm{OH})_3(\mathrm{~s})\) 10. Write a proper formation reaction for each substance. a. \mathrm{O}_3(\mathrm{~g}) b. \(\quad \mathrm{Na}_2 \mathrm{O}_2(\mathrm{~s})\) c. \(\mathrm{PCl}_5(\mathrm{~g})\) 11. Write this reaction in terms of formation reactions. \( \quad \quad \quad \mathrm{MgCO}_3(\mathrm{~s}) \rightarrow \mathrm{MgO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g}) \notag \) 12. Write this reaction in terms of formation reactions. \( \quad \quad \quad 2 \mathrm{NO}+4 \mathrm{NO}_2 \rightarrow 2 \mathrm{~N}_2 \mathrm{O}_5+\mathrm{N}_2 \notag \) 13. Write this reaction in terms of formation reactions. \( \quad \quad \quad 2 \mathrm{CuCl}(\mathrm{s}) \rightarrow \mathrm{Cu}(\mathrm{s})+\mathrm{CuCl}_2(\mathrm{~s}) \notag \) 14. Write this reaction in terms of formation reactions. \( \quad \quad \quad \mathrm{SiH}_4+4 \mathrm{~F}_2 \rightarrow \mathrm{SiF}_4+4 \mathrm{HF} \notag \) 15. Determine the enthalpy change of this reaction. Data can be found in Table 7.2 "Enthalpies of Formation for Various Substances". \( \quad \quad \quad \mathrm{CH}_2 \mathrm{O}(\mathrm{g})+\mathrm{O}_2 \rightarrow \mathrm{CO}_2(\mathrm{~g})+\mathrm{H}_2 \mathrm{O}(\ell) \notag \) 16. Determine the enthalpy change of this reaction. Data can be found in Table 7.2 "Enthalpies of Formation for Various Substances". \( \quad \quad \quad 2 \mathrm{AgBr}(\mathrm{s})+\mathrm{Cl}_2(\mathrm{~g}) \rightarrow 2 \mathrm{AgCl}(\mathrm{s})+\mathrm{Br}_2(\ell) \notag \) 17. Determine the enthalpy change of this reaction. Data can be found in Table 7.2 "Enthalpies of Formation for Various Substances". \( \quad \quad \quad \mathrm{Mg}(\mathrm{s})+\mathrm{N}_2 \mathrm{O}_5(\mathrm{~g}) \rightarrow \mathrm{MgO}(\mathrm{s})+2 \mathrm{NO}_2(\mathrm{~g}) \notag \) 18. Determine the enthalpy change of this reaction. Data can be found in Table 7.2 "Enthalpies of Formation for Various Substances". \( \quad \quad \quad 2 \mathrm{C}_6 \mathrm{H}_6(\mathrm{l})+15 \mathrm{O}_2(\mathrm{~g}) \rightarrow 12 \mathrm{CO}_2(\mathrm{~g})+6 \mathrm{H}_2 \mathrm{O}(\ell) \notag \) Answers 1. A formation reaction is a reaction that produces one mole of a substance from its elements. Example: \(\mathrm{C}(\mathrm{s})+\mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}_2(\mathrm{~g})\) 3. a. formation reaction b. It is not the formation of a single substance, so it is not a formation reaction. 5. a. formation reaction b. It is not the formation of a single substance, so it is not a formation reaction. 7. a. \(3 / 2 \mathrm{H}_2(\mathrm{~g})+\mathrm{P}(\mathrm{s})+2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{H}_3 \mathrm{PO}_4(\mathrm{~s})\) b. \(2 \mathrm{Na}(\mathrm{s})+1 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{Na}_2 \mathrm{O}(\mathrm{s})\) c. \(3 \mathrm{C}(\mathrm{s})+1 / 2 \mathrm{O}_2(\mathrm{~g})+4 \mathrm{H}_2(\mathrm{~g}) \rightarrow \mathrm{C}_3 \mathrm{H}_7 \mathrm{OH}(\mathrm{\ell})\) 9. a. \(12 \mathrm{C}(\mathrm{s})+11 \mathrm{H}_2(\mathrm{~g})+11 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(\mathrm{~s})\) b. \(\mathrm{Zn}(\mathrm{s})+\mathrm{N}_2(\mathrm{~g})+3 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{Zn}\left(\mathrm{NO}_3\right)_2\) c. \(\mathrm{Al}(\mathrm{s})+3 / 2 \mathrm{O}_2(\mathrm{~g})+3 / 2 \mathrm{H}_2(\mathrm{~g}) \rightarrow \mathrm{Al}(\mathrm{OH})_3(\mathrm{~s})\) 11. a. \(\mathrm{MgCO}_3(\mathrm{~s}) \rightarrow \mathrm{Mg}(\mathrm{s})+\mathrm{C}(\mathrm{s})+3 / 2 \mathrm{O}_2(\mathrm{~g})\) b. \(\mathrm{Mg}(\mathrm{s})+1 / 2 \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{MgO}(\mathrm{s})\) c. \(\mathrm{C}(\mathrm{s})+\mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{CO}_2(\mathrm{~g})\) 13. a. \(2 \times\left[\mathrm{CuCl}(\mathrm{s}) \rightarrow \mathrm{Cu}(\mathrm{s})+1 / 2 \mathrm{Cl}_2(\mathrm{~g})\right]\) b. \(\mathrm{Cu}(\mathrm{s}) \rightarrow \mathrm{Cu}(\mathrm{s})\) c. \(\mathrm{Cu}(\mathrm{s})+\mathrm{Cl}_2(\mathrm{~g}) \rightarrow \mathrm{CuCl}_2(\mathrm{~s})\) 15. \(\Delta H=-563.44 \mathrm{~kJ}\) 17. \(\Delta H=-546.7 \mathrm{~kJ}\) Additional Exercises What is the work when 124 mL of gas contract to 72.0 mL under an external pressure of 822 torr? What is the work when 2,345 mL of gas contract to 887 mL under an external pressure of 348 torr? A 3.77 L volume of gas is exposed to an external pressure of 1.67 atm. As the gas contracts, 156 J of work are added to the gas. What is the final volume of the gas? A 457 mL volume of gas contracts when 773 torr of external pressure act on it. If 27.4 J of work are added to the gas, what is its final volume? What is the heat when 1,744 g of Hg increase in temperature by 334°C? Express your final answer in kJ. What is the heat when 13.66 kg of Fe cool by 622°C? Express your final answer in kJ. What is final temperature when a 45.6 g sample of Al at 87.3°C gains 188 J of heat? What is final temperature when 967 g of Au at 557°C lose 559 J of heat? Plants take CO 2 and H 2 O and make glucose (C 6 H 12 O 6 ) and O 2 . Write a balanced thermochemical equation for this process. Use data in Table \(\PageIndex{1}\) of Section 7.7 Exercise 9 described the formation of glucose in plants, which take in CO 2 and H 2 O and give off O 2 . Is this process exothermic or endothermic? If exothermic, where does the energy go? If endothermic, where does the energy come from? The basic reaction in the refining of aluminum is to take Al 2 O 3 (s) and turn it into Al(s) and O 2 (g). Write the balanced thermochemical equation for this process. Use data in Table \(\PageIndex{1}\) of Section 7.7 Is the enthalpy change of the reaction H 2 O(ℓ) → H 2 O(g) zero or nonzero? Use data in Table \(\PageIndex{1}\) of Section 7.7 What mass of H 2 O can be heated from 22°C to 80°C in the combustion of 1 mol of CH 4 ? You will need the balanced thermochemical equation for the combustion of CH 4 . Use data in Table \(\PageIndex{1}\) of Section 7.7 What mass of H 2 O can be heated from 22°C to 80°C in the combustion of 1 mol of C 2 H 6 ? You will need the balanced thermochemical equation for the combustion of C 2 H 6 . Use data in Table \(\PageIndex{1}\) of Section 7.7 What is the enthalpy change for the unknown reaction? Pb(s) + Cl 2 (g) → PbCl 2 (s) Δ H = −359 kJPbCl 2 (s) + Cl 2 (g) → PbCl 4 (ℓ) Δ H = ?Pb(s) + 2Cl 2 (g) → PbCl 4 (ℓ) Δ H = −329 kJ What is the enthalpy change for the unknown reaction? P(s) + 3/2Br 2 (ℓ) → PBr 3 (ℓ) Δ H = −185 kJPI 3 (s) → P(s) + 3/2I 2 (s) Δ H = ?PI 3 (s) + 3/2Br 2 (ℓ) → PBr 3 (ℓ) + 3/2I 2 (s) Δ H = −139 kJ What is the Δ H for this reaction? The label gra means graphite, and the label dia means diamond. What does your answer mean? C(s, gra) → C(s, dia) Without consulting any tables, determine the Δ H for this reaction. Explain your answer. H 2 O(ℓ, 25°C) → H 2 O(ℓ, 25°C) Answers 1. 4.69 L 3. 80.97 kJ 5. 91.9°C 7. 6CO 2 (g) + 6H 2 O(ℓ) → C 6 H 12 O 6 (s) + 6O 2 (g) Δ H = 2,799 kJ 9. 2Al 2 O 3 (s) → 4Al(s) + 3O 2 (g) Δ H = 3351.4 kJ 11. 3,668 g 13. Δ H = 30 kJ 15. 5.70 J 17. Δ H = 1.897 kJ; the reaction is endothermic.