Enthalpy of reaction Knowledge-Based Practice

Questions

1. 1.

   Under which of the following conditions is the heat exchanged by a chemical reaction system ($q$) directly equal to the enthalpy change of the reaction ($\Delta H$)?

   • A) Constant volume when no non-expansion work is done
   • B) Constant pressure when only pressure-volume work is done
   • C) Constant temperature when the system is thermally isolated
   • D) Constant internal energy when non-expansion electrical work is done
2. 2.

   Using the average bond enthalpies of 436 kJ/mol for H–H, 242 kJ/mol for Cl–Cl, and 431 kJ/mol for H–Cl, what is the enthalpy of reaction, $\Delta H^\circ_\text{rxn}$, for the gas-phase reaction $\text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g)$?

   • A) +184 kJ
   • B) −184 kJ
   • C) −92 kJ
   • D) +247 kJ
3. 3.

   Consider the thermochemical equation $2\text{CO}(g) + \text{O}_2(g) \rightarrow 2\text{CO}_2(g)$ with $\Delta H^\circ = -566.0\text{ kJ}$. What is the enthalpy change when 14.0 g of CO(g) reacts completely with excess oxygen? (Molar mass of CO = 28.0 g/mol)

   • A) -283.0 kJ
   • B) -141.5 kJ
   • C) +141.5 kJ
   • D) -566.0 kJ
4. 4.

   Given the thermochemical equations $\text{S}(s) + \text{O}_2(g) \rightarrow \text{SO}_2(g)$ with $\Delta H^\circ = -296.8\text{ kJ}$ and $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$ with $\Delta H^\circ = -198.4\text{ kJ}$, what is the standard enthalpy of reaction, $\Delta H^\circ$, for $2\text{S}(s) + 3\text{O}_2(g) \rightarrow 2\text{SO}_3(g)$?

   • A) $-792.0\text{ kJ}$
   • B) $-495.2\text{ kJ}$
   • C) $-395.2\text{ kJ}$
   • D) $+792.0\text{ kJ}$
5. 5.

   Given the standard enthalpies of formation: $\Delta H_\text{f}^\circ[\text{CH}_4(g)] = -74.8\text{ kJ/mol}$, $\Delta H_\text{f}^\circ[\text{CO}_2(g)] = -393.5\text{ kJ/mol}$, and $\Delta H_\text{f}^\circ[\text{H}_2\text{O}(l)] = -285.8\text{ kJ/mol}$, what is the standard enthalpy of reaction, $\Delta H^\circ_\text{rxn}$, for the combustion of methane represented by $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$?

   • A) $-890.3\text{ kJ}$
   • B) $-604.5\text{ kJ}$
   • C) $+890.3\text{ kJ}$
   • D) $-1039.9\text{ kJ}$

Answers and step-by-step solutions appear after you finish the test.