Question

What happens when ΔH and ΔS are both negative?"

A) Reaction is spontaneous.
B) Reaction is non-spontaneous.
C) Depends on temperature.
D) Equilibrium is reached.

Answer 1

The spontaneity of a reaction where both ΔH and ΔS are negative depends on temperature, because ΔG = ΔH - TΔS and the outcome is temperature-dependent.

Step-by-step explanation:

When ΔH (enthalpy change) and ΔS (entropy change) are both negative, the spontaneity of a reaction depends on the temperature. According to the Gibbs free energy equation, ΔG = ΔH - TΔS, where T is the temperature in Kelvin. Since ΔH is negative, the first term is negative; however, because ΔS is also negative, the second term (-TΔS) will become positive at any positive temperature value. Therefore, the spontaneity will depend on whether the positive -TΔS term is sufficient to outweigh the negative ΔH term.

At low temperatures, the ΔG may be negative, making the reaction spontaneous. Conversely, at high temperatures, the -TΔS term may dominate and ΔG becomes positive, hence the reaction is non-spontaneous. Therefore, the correct answer is C) Depends on temperature.