What does enthalpy change refer to in a chemical reaction?

Enthalpy change in a chemical reaction specifically refers to the heat change that occurs during the reaction, either being absorbed from the surroundings or evolved to the surroundings. This is indicative of the energy transfer involved in breaking and forming chemical bonds as reactants convert to products. When a reaction absorbs heat, it is endothermic and results in a positive enthalpy change. Conversely, when heat is released, it is exothermic, resulting in a negative enthalpy change.

This concept is integral to thermodynamics in chemistry, as it helps predict the behavior of reactions in different conditions and can also provide insight into reaction spontaneity. Understanding enthalpy change is crucial for calculating reaction energy profiles and assessing reaction feasibility. Other options, while they pertain to different aspects of chemical reactions, do not accurately represent the specific concept of enthalpy change. For instance, pressure change is related to gas laws, mass change relates to conservation of mass, and color change is often an observable physical change that may indicate a reaction but does not quantify energy changes.