The enthalpy change of a chemical reaction is the amount of heat that is absorbed or released by the reaction at constant pressure. If the enthalpy change of a reaction is positive, then the reaction is endothermic and heat is absorbed from the surroundings. If the enthalpy change of a reaction is negative, then the reaction is exothermic and heat is released to the surroundings.
The entropy change of a chemical reaction is the change in the degree of disorder of the system during the reaction. If the entropy change of a reaction is positive, then the reaction is spontaneous and will occur without the need for an external energy source. If the entropy change of a reaction is negative, then the reaction is non-spontaneous and will not occur without the need for an external energy source.
The Gibbs free energy change of a chemical reaction is the energy that is available to do work during the reaction. If the Gibbs free energy change of a reaction is negative, then the reaction is spontaneous and will occur without the need for an external energy source. If the Gibbs free energy change of a reaction is positive, then the reaction is non-spontaneous and will not occur without the need for an external energy source.
In summary, chemical reactions always involve a change in energy because they involve the breaking and forming of chemical bonds. The amount of energy that is absorbed or released during a chemical reaction depends on the strength of the chemical bonds that are broken and formed. The enthalpy change, entropy change, and Gibbs free energy change of a chemical reaction are all important factors that determine whether the reaction will be spontaneous or non-spontaneous.
