What does a positive heat of reaction indicate about the reaction process?

A positive heat of reaction indicates that the reaction absorbs heat from its surroundings, characterizing it as an endothermic reaction. In thermodynamic terms, when a reaction has a positive enthalpy change (ΔH > 0), it means that energy is required for the reaction to proceed. As a result, the system takes in heat, leading to a decrease in the temperature of the surroundings if no additional heat is supplied. This is a fundamental principle in thermochemistry and helps in understanding how energy flows during chemical processes.

Endothermic reactions are commonly seen in processes such as melting ice or evaporating water, where energy is needed to break intermolecular forces. Thus, recognizing that a positive heat of reaction signifies an endothermic process is pivotal for predicting how reactions will behave under varying conditions of temperature and pressure.