Question

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

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

Answer 1

Answer: (B)

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

For the reaction $A\left(g\right)\to A\left(l\right)$

The change in the number of moles of gaseous species $\Delta n=0-1=-1$

The enthalpy change $\Delta H=-3RT$

$\Delta H=\Delta U+\Delta nRT$

$-3RT=\Delta U+(-1)RT$

The change in internal energy $\Delta U=-2RT$

Hence, $|\Delta H|>|\Delta U|$