Standard Enthalpy of Formation — Prelims Questions

Given the following standard enthalpies of formation: $\Delta H_f^\circ(\text{C}_2\text{H}_5\text{OH}(\text{l})) = -277.7\,\text{kJ/mol}$ $\Delta H_f^\circ(\text{CO}_2(\text{g})) = -393.5\,\text{kJ/mol}$ $\Delta H_f^\circ(\text{H}_2\text{O}(\text{l})) = -285.8\,\text{kJ/mol}$ Calculate the standard enthalpy of combustion for ethanol, $\text{C}_2\text{H}_5\text{OH}(\text{l})$, according to the reaction: $\text{C}_2\text{H}_5\text{OH}(\text{l}) + 3\text{O}_2(\text{g}) \rightarrow 2\text{CO}_2(\text{g}) + 3\text{H}_2\text{O}(\text{l})$

Which of the following equations represents the standard enthalpy of formation of $\text{HCl}(\text{g})$?

The standard enthalpy of formation of $\text{NH}_3(\text{g})$ is $-46.1\,\text{kJ/mol}$. What is the enthalpy change for the reaction: $2\text{NH}_3(\text{g}) \rightarrow \text{N}_2(\text{g}) + 3\text{H}_2(\text{g})$?

Which of the following statements about standard enthalpy of formation is INCORRECT?

Given the following data: $\text{C}(\text{graphite}) + \text{O}_2(\text{g}) \rightarrow \text{CO}_2(\text{g})$, $\Delta H^\circ = -393.5\,\text{kJ}$ $\text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\text{l})$, $\Delta H^\circ = -285.8\,\text{kJ}$ $\text{C}_2\text{H}_6(\text{g}) + \frac{7}{2}\text{O}_2(\text{g}) \rightarrow 2\text{CO}_2(\text{g}) + 3\text{H}_2\text{O}(\text{l})$, $\Delta H^\circ = -1560\,\text{kJ}$ Calculate the standard enthalpy of formation of ethane, $\text{C}_2\text{H}_6(\text{g})$.

The standard enthalpy of formation of $\text{H}_2\text{O}(\text{g})$ is $-241.8\,\text{kJ/mol}$, and the standard enthalpy of formation of $\text{H}_2\text{O}(\text{l})$ is $-285.8\,\text{kJ/mol}$. What is the standard enthalpy of vaporization of water at $298\,\text{K}$?