Which of the following graphs correctly represents the variation of thermodynamic properties of Haber's process? (N2(g)…

🧠 Haber's process: $\Delta H < 0$ and $\Delta S < 0$ — both properties decrease with temperature in a Ellingham-style plot For $\ce{N2 + 3H2 -> 2NH3}$: the reaction is exothermic ($\Delta H_R < 0$) and entropy decreases ($\Delta S_R < 0$) because gas moles decrease from 4 to 2.

Analyzing the thermodynamic plots:

• $-\Delta H_R^\circ / T$ increases as $T$ increases (since $\Delta H_R$ is roughly constant, dividing by larger $T$ reduces the magnitude of the negative value, making $-\Delta H / T$ less positive).
• $-\Delta S_R^\circ$ is constant and positive (since $\Delta S_R < 0$, its negation is $> 0$).
• $-\Delta G_R^\circ / T = -\Delta H_R^\circ / T + \Delta S_R^\circ$ decreases with temperature (the positive entropy term gets subtracted increasingly by the diminishing $-\Delta H/T$ contribution).

Graph (a) correctly shows $-\Delta H/T$ decreasing, $-\Delta S$ constant and positive, and $-\Delta G/T$ decreasing.

$\boxed{\text{Answer: (a)}}$