Question

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

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

We know that

$\Delta H=\Delta E+\Delta \left(PV\right)\Delta H=\Delta E+\Delta \left(nRT\right)$

When number of moles in product is less than number of moles in reactant.

So, $\Delta n=-ve$

So, $\Delta H<\Delta E$.

So, option D is correct.