$\Delta H = \Delta U + \Delta {n_g}RT$
Given, $\Delta H = - 3RT$
Here
$\Delta {n_g} = {n_p} - {n_r} = 0 - 1 = - 1$
$\Delta H = \Delta U - RT$
$ \Rightarrow - 3RT = \Delta U - RT$
$ \Rightarrow - 3RT + RT = \Delta U$
$ \Rightarrow - 2RT = \Delta U$
$|\Delta H|\, > \,|\Delta U|$
( $373\, K$ તાપમાને પાણી નું $\Delta H _{\text {vap }}$ $K =41$ કિલોજૂલ/મોલ $\left. R =8.314\, JK ^{-1} mol ^{-1}\right)$)