The standard enthalpy of reaction of N₂(g) + 3 H₂(g) → 2 NH₃ g) is –92.22 kJ · mol^–1 at 298 K. The industrial synthesis takes place at 450. °C. What is the standard reaction enthalpy at the latter temperature?

ANTICIPATE There are more reactant molecules than product molecules, so you should suspect that the heat capacity of the products is less than that of the reactants and, therefore, that ΔC_P is negative. If that is so, an increase in temperature will make ΔH more negative and therefore the reaction more exothermic.

PLAN Calculate the difference in heat capacities of the reactants and products using Eq. 4, then use Eq. 3 to solve for ΔH°(T₂).

(T,) = (T;) + (T, T) Cp (3)