What is the value of $\Delta \mathrm{H}-\Delta \mathrm{U}$ for the formation of 2 moles of ammonia from…
What is the value of $\Delta \mathrm{H}-\Delta \mathrm{U}$ for the formation of 2 moles of ammonia from $\mathrm{H}_{2(\mathrm{~g})}$ and $\mathrm{N}_{2(\mathrm{~g})}$ ?
$-\frac{\mathrm{RT}}{2}$
$\frac{\mathrm{RT}}{2}$
$-2 \mathrm{RT}$
$2 \mathrm{RT}$
Solution
$\begin{aligned} & \mathrm{N}_{2(\mathrm{~g})}+3 \mathrm{H}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{NH}_{3(\mathrm{~g})} \\ & \Delta \mathrm{H}-\Delta \mathrm{U}=\Delta \mathrm{n}_{\mathrm{g}} \cdot \mathrm{RT} \\ & \Delta \mathrm{n}_{\mathrm{g}}=[\text { Sum of stoichiometric coefficients of gaseous products] } \\ & -[\text { Sum of stoichiometric coefficients of gaseous reactant] } \\ & \Delta \mathrm{n}_{\mathrm{g}}=2-1-3=-2 \\ & \Delta \mathrm{H}-\Delta \mathrm{U}-2 \mathrm{RT}\end{aligned}$