Question

The reaction shown below has a positive enthalpy change and a negative entropy change. 2C (s) + 2H2 (g) yields C2H4 (g) Which of the following best describes this reaction?

The reaction will be spontaneous at any temperature.
The reaction will not be spontaneous at any temperature.
The reaction will only be spontaneous at low temperatures.
The reaction will only be spontaneous at high temperatures.

Answer 1

Answer is: The reaction will not be spontaneous at any temperature.

Gibbs free energy (G) determines if reaction will proceed spontaneously.
ΔG = ΔH - T·ΔS.
ΔG - changes in Gibbs free energy.
ΔH - changes in enthalpy.
ΔS - changes in entropy.
T is temperature in Kelvins.
When ΔS < 0 (negative entropy change) and ΔH > 0 (endothermic reaction), the process is never spontaneous (ΔG> 0).