Question

For which of the following reactions, $\Delta H$ is equal to $\Delta U$ ?

• A. $N_2(g) + 3H2(g) -> 2NH_3(g)$
• B. $2HI(g) -> H_2(g) + I_2(g)$
• C. $2NO_2(g) -> N_2O_4(g)$
• D. $2SO_2(g) + O_2(g) -> 2SO_3(g)$

Answer 1

Answer: (B)

We know $\Delta H=\Delta U+\Delta n_{g} R T$

where $\Delta n_{ g }=$ gaseous moles of products - gaseous moles of reactants

For reaction $2 HI ( g ) \rightarrow H _{2}( g )+ I _{2}( g ) ;\, \Delta n_{ g }=2-2=0$

Therefore, from Eq. (1), we get

$\Delta H=\Delta U$