Question

If a reaction $△H<0$ and $△S<0$, the reaction proceeds furthest in the forward direction and is at?

• A. Low temperature
• B. High temperature
• C. All temperature
• D. No temperature

Answer 1

The correct option is B High temperature

Taking example of Ammonia synthesis.

$3H_2+N_2=2N{H}_3\left(g\right)$

$\Delta H^0=–46.2$ kJ

$\Delta S^0=–389$ J $K^{-1}$

$\Delta G^0=–16.4$ kJ at 298 K

The decrease in moles of gas in the Haber ammonia synthesis drives the entropy change negative, making the reaction spontaneous only at low temperatures. Thus higher T, which speeds up the reaction, also reduces its extent.