What type of reaction typically has a positive enthalpy change?

A reaction that typically has a positive enthalpy change is an endothermic reaction. In thermodynamics, the enthalpy change (ΔH) indicates the heat absorbed or released during a reaction at constant pressure. An endothermic reaction is characterized by the absorption of heat from the surroundings, which results in a positive value for enthalpy change.

During an endothermic reaction, energy is required to break bonds in the reactants, and since this energy must be absorbed from the surroundings, the reaction leads to a decrease in the temperature of the surroundings, thereby reflecting a positive enthalpy change.

In contrast, exothermic reactions release heat, resulting in a negative enthalpy change. Spontaneous reactions may be exothermic or endothermic, depending on factors like temperature and entropy changes, and not all spontaneous reactions have a positive enthalpy change. Redox reactions, which involve the transfer of electrons, can be either exothermic or endothermic depending on the specific substances involved, so they do not consistently correspond to a positive enthalpy change.