What does it mean when a reaction has a positive change in enthalpy (+∆H)?

When a reaction has a positive change in enthalpy (+∆H), it indicates that the system is absorbing heat from the surroundings. This characteristic defines an endothermic reaction, where the energy required to break bonds in the reactants exceeds the energy released during the formation of products. As a result, the reaction draws heat in from its environment, leading to a temperature decrease in the surrounding area.

In the context of thermodynamics, an endothermic process contrasts with exothermic reactions, which release heat, corresponding to a negative change in enthalpy (-∆H). Understanding this concept is vital for predicting the thermal behavior of chemical reactions and their suitability for specific conditions in biological and chemical processes.