Thermochemical equations Knowledge-Based Download PDF

Questions

1. 1.

   Which of the following thermochemical equations represents the reaction for the standard molar enthalpy of formation, $\Delta H^\circ_f$, of liquid methanol, $\text{CH}_3\text{OH}(l)$?

   • A) $\text{CO}(g) + 2\text{H}_2(g) \rightarrow \text{CH}_3\text{OH}(l)$
   • B) $\text{C}(s, \text{diamond}) + 2\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{CH}_3\text{OH}(l)$
   • C) $2\text{C}(s, \text{graphite}) + 4\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{CH}_3\text{OH}(l)$
   • D) $\text{C}(s, \text{graphite}) + 2\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{CH}_3\text{OH}(l)$
2. 2.

   Which of the following statements correctly describes the conventions and interpretation of balanced thermochemical equations?

   • A) Reversing the direction of a chemical equation leaves the algebraic sign of the enthalpy change unchanged.
   • B) The physical states of substances are omitted because phase changes do not affect the enthalpy of reaction.
   • C) Fractional stoichiometric coefficients are not allowed because fractional quantities cannot participate in a reaction.
   • D) The stoichiometric coefficients correspond to the exact number of moles of substances that produce the stated enthalpy change.
3. 3.

   Given the thermochemical equations $\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(l)$ with $\Delta H^\circ = -285.8\text{ kJ}$ and $\text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(g)$ with $\Delta H^\circ = -241.8\text{ kJ}$, what is the standard enthalpy change for the vaporization of one mole of liquid water, $\text{H}_2\text{O}(l) \rightarrow \text{H}_2\text{O}(g)$?

   • A) -527.6 kJ
   • B) +44.0 kJ
   • C) -44.0 kJ
   • D) +527.6 kJ
4. 4.

   Given the thermochemical equation $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$ with $\Delta H = -198\text{ kJ}$, what is the enthalpy change for the reaction $\text{SO}_3(g) \rightarrow \text{SO}_2(g) + \frac{1}{2}\text{O}_2(g)$?

   • A) $-99\text{ kJ}$
   • B) $+99\text{ kJ}$
   • C) $-198\text{ kJ}$
   • D) $+396\text{ kJ}$
5. 5.

   According to the thermochemical equation $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ with $\Delta H^\circ = -890.4\text{ kJ}$, what quantity of heat is released upon the complete combustion of 32.0 g of $\text{CH}_4(g)$ in excess oxygen? (Molar mass of $\text{CH}_4 = 16.0\text{ g/mol}$)

   • A) 1780.8 kJ
   • B) 890.4 kJ
   • C) 445.2 kJ
   • D) 3561.6 kJ