Question

For a reaction : $C_{\left(s\right) }+ O_{2\left(g\right)} \to CO_{2\left(g\right)}$
What is the relation between enthalpy of reaction $(\Delta H_r)$, enthalpy of formation of $CO_2\, (\Delta H_f)$ and enthalpy of combustion of carbon $(\Delta H_{comb})$?

• A. $\Delta H_{r} > \Delta H_{f} = \Delta H_{comb}$
• B. $\Delta H_{r} = \Delta H_{f} = \Delta H_{comb}$
• C. $\Delta H_{r} = \Delta H_{f} + \Delta H_{comb}$
• D. $\Delta H_{r} = 2 \times \Delta H_{f} $

Answer 1

Answer: (B)

Since the reaction shows combustion of one mole of carbon, $\Delta H_{reaction}$ is enthalpy of combustion since $1$ mole of $CO_2$ is formed. $\Delta H_{reaction}$ is also the enthalpy of formation of $CO_2$.