Question

In which of the following reactions, ∆H is greater than ∆U?

Options

• \[\ce{N2_{(g)} + 3H2_{(g)} -> 2NH3_{(g)}}\]

• \[\ce{PCl5_{(g)} -> PCl3_{(g)} + Cl2_{(g)}}\]

• \[\ce{CH4_{(g)} + 2O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}}\]

• \[\ce{HCl_{(aq)} + NaOH_{(aq)} -> NaCl_{(aq)} + H2O_{(aq)}}\]

Answer 1

\[\ce{PCl5_{(g)} -> PCl3_{(g)} + Cl2_{(g)}}\]

Explanation:

In the reaction, \[\ce{PCl5_{(g)} -> PCl3_{(g)} + Cl2_{(g)}}\]

∆n = 2 − 1 = +1

∆H = ∆U + ∆n_gRT

∴ ∆H > ∆U