Question

For a reaction, ${A_(g) \to A_(l); \Delta H = - 3RT}$. The correct statement for the reaction is :

• A. $\Delta H = \Delta U \neq O$
• B. $\Delta H = \Delta U = O$
• C. $| \Delta H| < | \Delta U|$
• D. $| \Delta H| > | \Delta U|$

Answer 1

Answer: (D)

$| \Delta H| > | \Delta U|$

Answer 2

For the reaction $A ( g ) \rightarrow A ( l )$ The change in the number of moles of gaseous species $\Delta n =0-1=-1$ The enthalpy change $\Delta H =-3 RT$ $\Delta H =\Delta U +\Delta nRT$ $-3 R T=\Delta U+(-1) R T$ The change in internal energy $\Delta U =-2 RT$ Hence, $|\Delta H |>|\Delta U |$