Question

Heat of reaction at constant pressure and heat of reaction at constant volume for the gaseous reaction $N_2+3H_2⟶2N{H}_3$ differ $(\Delta H-\Delta U)$ by the amount:

• A. $2RT$
• B. $-2RT$
• C. $3RT$
• D. $RT$

Answer 1

The correct option is B $-2RT$

The heat of reaction at constant pressure and heat of reaction at constant volume for the gaseous reaction

$N_2+3H_2⟶2N{H}_3$

$\Delta H=\Delta U+\left(\Delta n_g\right)\times RT$

$\Delta H=\Delta U+(-2)\times RT$

This is because the change in the number of moles of gaseous products and the gaseous reactants in the above reaction is -2.

$\Delta H-\Delta U=(-2)\times RT$

Hence, option B is correct.