Hess's Law Practice Test

Use Hess’s law to determine $\Delta H$ for: $\mathrm{2C(s) + 3H_2(g) \rightarrow C_2H_6(g)}$. The following reactions are given:

1. $\mathrm{2C(s) + 2H_2(g) \rightarrow C_2H_4(g)}$ $\Delta H = +52\ \mathrm{kJ}$

2. $\mathrm{C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)}$ $\Delta H = -149\ \mathrm{kJ}$

Use Hess’s law to find $\Delta H$ for: $\mathrm{CO(g) + \tfrac{1}{2}O_2(g) \rightarrow CO_2(g)}$. The following reactions are given:

1. $\mathrm{C(s) + O_2(g) \rightarrow CO_2(g)}$ $\Delta H = -394\ \mathrm{kJ}$

2. $\mathrm{C(s) + \tfrac{1}{2}O_2(g) \rightarrow CO(g)}$ $\Delta H = -111\ \mathrm{kJ}$