For N2(g) + 3H2(g) -> 2NH3(g), Delta H deg_298 = -92.2 kJ. Molar heat capacities C_p/J mol^-1K^-1: N2 = 29.1, H2 = 28.8, NH3 = 35.1 (temperature independent). The enthalpy change at 400 K is

JEE Advanced levelSingle correct optionDifficulty 3 of 3td091

For $N X_{2} (g) + 3 H X_{2} (g) 2 NH X_{3} (g)$ , $Δ H_{298}^{\circ} = - 92.2 kJ$ . Molar heat capacities $C_{p} / J mo l^{- 1} K^{- 1}$ : $N X_{2} = 29.1$ , $H X_{2} = 28.8$ , $NH X_{3} = 35.1$ (temperature independent). The enthalpy change at $400 K$ is

Kirchhoff's law:

Δ H_{400} = Δ H_{298} + Δ C_{p} Δ T

Δ C_{p} = 2 (35.1) - [29.1 + 3 (28.8)] = - 45.3 J K^{- 1}

. So

Δ H_{400} = - 92.2 + (- 45.3) (102) /1000 = - 96.8 kJ