Question

An endothermic reaction has a positive internal energy change $\Delta E$. In such a case, what is the minimum value that the activation energy can have?

• A. $ \Delta E $
• B. $ \Delta E=\Delta H+\Delta n_{g}RT $
• C. $ \Delta E=\Delta H-\Delta n_{g}RT $
• D. $ \Delta E=E_{a}+RT $

Answer 1

Answer: (C)

From first law of thermodynamics,
we have $\Delta E=Q+W \ldots$ (i)
Here, $\Delta E=$ change in internal energy,
$=\Delta E Q =$ heat of the reaction
$=\Delta H W =$ work done
$=-P \Delta V(\because$ Reaction is endothermic. $)$
$=\Delta n_{g} R T$ Thus, Eq. (i)
becomes $\Delta E=\Delta H-\Delta n_{g} R T$