Question

In which of the following reactions, ΔH is not equal to ΔU?

Options

• \[\ce{SO_{2(g)} + NO_{2(g)} -> SO_{3(g)} + NO_{(g)}}\]

• \[\ce{N_{2(g)} + O_{2(g)} -> 2NO_{(g)}}\]

• \[\ce{H_{2(g)} + I_{2(g)} -> 2HI_{(g)}}\]

• \[\ce{2SO_{2(g)} + O_{2(g)} -> 2SO_{3(g)}}\]

Answer 1

\[\ce{2SO_{2(g)} + O_{2(g)} -> 2SO_{3(g)}}\]

Explanation:

ΔH = ΔU + Δn_gRT

If Δn_g = 0, then ΔH = ΔU

\[\ce{2SO_{2(g)} + O_{2(g)} -> 2SO_{3(g)}}\]

Δn_g = - 1

ΔH ≠ ΔU

In all other reactions Δn_g = 0 ⇒ ΔH = ΔU