Advanced Placement (AP) Chemistry Practice Exam

Enthalpy of combustion is defined specifically as the heat released when one mole of a substance is burned completely in oxygen. This process involves a combustion reaction, which is a type of exothermic reaction where the products typically include carbon dioxide and water, depending on the nature of the burning substance. The measurement of this heat release is important for understanding the energy content of fuels, the efficiency of combustion processes, and the environmental impacts of burning various materials.

The concept highlights that combustion reactions are characterized by their tendency to release energy, which is a fundamental aspect in thermodynamics. The unit of measurement for this enthalpy change is usually expressed in kilojoules per mole (kJ/mol). This contrasts entirely from other options—freezing a substance, phase changes, and breaking chemical bonds—each of which describes different thermodynamic processes not related to combustion specifically.