Change in enthalpy also affects entropy. For an endothermic reaction, heat is absorbed from the surroundings, so, the entropy of the surroundings decreases. For exothermic reactions, heat is released to the surroundings, so, the entropy of the surroundings increases. Enthalpy (∆H) and entropy (∆S) are related to each other by a chemical formula: ΔG = ΔH – TΔS; where ΔG is the change in free energy.