9. Thermochemistry

Enthalpy Changes — Quiz

Test your understanding of enthalpy changes with 5 practice questions.

Practice Questions

Question 1

What is the enthalpy change for the reaction: $C_2H_6 (g) + \frac{7}{2} O_2 (g) \rightarrow 2CO_2 (g) + 3H_2O (g)$, given: $\Delta H_f^\circ (C_2H_6) = -84.7 \, kJ/mol$, $\Delta H_f^\circ (CO_2) = -393.5 \, kJ/mol$, $\Delta H_f^\circ (H_2O (g)) = -241.8 \, kJ/mol$?

Question 2

Which of the following correctly describes the enthalpy change for the reaction: $N_2 (g) + 3Cl_2 (g) \rightarrow 2NCl_3 (g)$, given that $\Delta H_f^\circ (NCl_3) = 230.0 \, kJ/mol$, $\Delta H_f^\circ (N_2) = 0$, and $\Delta H_f^\circ (Cl_2) = 0$?

Question 3

Calculate the enthalpy change for the reaction: $C_3H_8 (g) + 5O_2 (g) \rightarrow 3CO_2 (g) + 4H_2O (g)$, given: $\Delta H_f^\circ (C_3H_8) = -103.8 \, kJ/mol$, $\Delta H_f^\circ (CO_2) = -393.5 \, kJ/mol$, $\Delta H_f^\circ (H_2O (g)) = -241.8 \, kJ/mol$.

Question 4

Which of the following reactions has the smallest (most positive) enthalpy change? (Given: $\Delta H_f^\circ (CH_4) = -74.8 \, kJ/mol$, $\Delta H_f^\circ (CO_2) = -393.5 \, kJ/mol$, $\Delta H_f^\circ (H_2O (l)) = -285.8 \, kJ/mol$, $\Delta H_f^\circ (H_2O (g)) = -241.8 \, kJ/mol$)

Question 5

Which of the following is the correct enthalpy change for the decomposition of 1 mole of $NH_4NO_3 (s)$ into $N_2O (g)$ and $2H_2O (g)$, given: $\Delta H_f^\circ (NH_4NO_3) = -365.6 \, kJ/mol$, $\Delta H_f^\circ (N_2O) = 82.0 \, kJ/mol$, $\Delta H_f^\circ (H_2O (g)) = -241.8 \, kJ/mol$?