Chemistry Regents Practice Test 2025 - Free Chemistry Regents Practice Questions and Study Guide

Enthalpy is a thermodynamic quantity that represents the total heat content of a system at constant pressure. It is expressed as the sum of the internal energy of the system plus the product of its pressure and volume. Enthalpy is particularly useful in understanding heat transfer in chemical reactions and physical processes.

When a chemical reaction occurs at constant pressure, the change in enthalpy (known as the enthalpy change) is equal to the heat absorbed or released by the system. This connection makes enthalpy an important factor in chemical thermodynamics, allowing chemists to predict whether a reaction will be endothermic (heat absorbed) or exothermic (heat released).

Other options describe different concepts: energy content refers to the amount of energy in a chemical, phase change temperature is a specific point in material science, and energy released during bond formation relates to bond enthalpy but does not capture the broader definition of enthalpy itself. Therefore, understanding enthalpy as the total heat content of a system is essential for explaining various energy-related changes during chemical processes.