Standard enthalpy of formation Knowledge-Based Download PDF

Questions

1. 1.

   The thermochemical equation for the synthesis of ammonia is $\text{N}_2(g) + 3\text{H}_2(g) \rightarrow 2\text{NH}_3(g)$ with $\Delta H^\circ = -92.2\text{ kJ}$. What is the standard enthalpy of formation, $\Delta H_f^\circ$, of $\text{NH}_3(g)$?

   • A) -184.4 kJ/mol
   • B) +46.1 kJ/mol
   • C) -46.1 kJ/mol
   • D) -92.2 kJ/mol
2. 2.

   The combustion of methane proceeds according to the equation $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ with $\Delta H^\circ = -890\text{ kJ/mol}$. Given that $\Delta H_f^\circ[\text{CO}_2(g)] = -394\text{ kJ/mol}$ and $\Delta H_f^\circ[\text{H}_2\text{O}(l)] = -286\text{ kJ/mol}$, what is the standard enthalpy of formation of $\text{CH}_4(g)$?

   • A) $-210\text{ kJ/mol}$
   • B) $-76\text{ kJ/mol}$
   • C) $+76\text{ kJ/mol}$
   • D) $-1856\text{ kJ/mol}$
3. 3.

   The standard enthalpies of formation of $\text{SO}_2(g)$ and $\text{SO}_3(g)$ are $-297\text{ kJ/mol}$ and $-396\text{ kJ/mol}$, respectively. What is the standard enthalpy change, $\Delta H^\circ$, for the reaction $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$?

   • A) $-99\text{ kJ}$
   • B) $+198\text{ kJ}$
   • C) $-198\text{ kJ}$
   • D) $+99\text{ kJ}$
4. 4.

   Which of the following substances has a standard enthalpy of formation ($\Delta H_f^\circ$) equal to zero at 298 K and 1 bar?

   • A) $H_2O(l)$
   • B) $Br_2(g)$
   • C) $C(\text{diamond})$
   • D) $I_2(s)$
5. 5.

   Which of the following chemical equations represents a reaction for which the standard enthalpy change of reaction is equal to the standard enthalpy of formation of the product?

   • A) $2\text{H}_2(g) + \text{O}_2(g) \rightarrow 2\text{H}_2\text{O}(l)$
   • B) $\text{CO}(g) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g)$
   • C) $\text{C}(\text{diamond}) + \text{O}_2(g) \rightarrow \text{CO}_2(g)$
   • D) $\text{C}(\text{graphite}) + 2\text{H}_2(g) \rightarrow \text{CH}_4(g)$