Question

Consider the reaction, N2 (g) + 3H2 (g) $\longrightarrow$ 2NH3 (g); carried out at constant temperature and pressure. If $\Delta$H and $\Delta$U are enthalpy change and internal energy change respectively, which of the following expressions is true ?

• A. $\Delta$H = 0
• B. $\Delta$H = $\Delta$U
• C. $\Delta$H <$\Delta$U
• D. $\Delta$H >$\Delta$U

Answer 1

Answer: (C)

$\Delta$H <$\Delta$U

Answer 2

N2 + 3H2 $\rightarrow$ 2NH3 $\Delta$n = 2 – 4 = – 2

$\Delta$H = $\Delta$U + $\Delta$nRT = $\Delta$U – 2RT. \ $\Delta$H < $\Delta$U.