Question

If $\Delta H$ is the change in enthalpy and $\Delta E$, the change in internal energy accompanying a gaseous reaction, then

• A. $\Delta H$ is always greater than $\Delta E$
• B. $\Delta H < \Delta E$ only if the number of moles of the products is greater than the number of moles of the reactants
• C. $\Delta H$ is always less than $\Delta E$
• D. $\Delta H < \Delta E$ only if the number of moles of products is less than the number of moles of the reactants

Answer 1

Answer: (D)

$\Delta H < \Delta E$ only if the number of moles of products is less than the number of moles of the reactants

Answer 2

As $\Delta H = \Delta E + \Delta n_g RT$
if $n_p < n_r; \Delta n_g = n_p - n_r = - ve.$
Hence $\Delta H < \Delta E.$