What kind of reaction occurs when the entropy change of an endothermic reaction is negative?

Answer is: reaction is nonspontaneous under standard conditions at all temperatures.

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 (endothermic reaction), the process is never spontaneous (ΔG> 0).