An exothermic reaction with ΔS < 0 will be:

An exothermic reaction with ΔS < 0 will be:

a. never spontaneous

b. always spontaneous

c. spontaneous at high enough temperatures.

d. spontaneous at low enough temperatures.

e. spontaneous with a low enough activation energy.

Solution:To determine whether a reaction is spontaneous, we look at Gibbs Free Energy (ΔG), which is given by the equation:

ΔG=ΔH−TΔS

Where:

ΔG = change in free energy

ΔH = change in enthalpy

T = temperature in Kelvin

ΔS = change in entropy

For a reaction to be spontaneous, ΔG must be negative.

In this case:

• The reaction is exothermic, so ΔH is negative.

• ΔS is negative.

Plugging this into the equation, the term –TΔS becomes positive, since T is always positive in Kelvin and ΔS is negative.

So, in order for ΔG to remain negative (and the reaction to be spontaneous), the magnitude of ΔH must be greater than TΔS. That only happens at low temperatures—otherwise the positive TΔS term will outweigh the negative ΔH.

Correct answer: d. spontaneous at low enough temperatures.

LINKS:

CHEMISTRY TUTOR ONLINE

GENERAL CHEMISTRY GUIDES

LEARNWITHMAYYA