In chemical systems, potential energy is often associated with bonds. It takes energy to break any type of molecular interaction, including chemical bonds and intermolecular interactions. This means that when a substance is heated, some of the energy goes into breaking these interactions. Energy that breaks the interactions do not actually affect the kinetic energy of the particles. This situation is often described with the phrase "energy is stored in chemical bonds," which is factually incorrect. Chemical bonds absorb energy to break and release energy to form.During a chemical reaction, substances rearrange themselves into new substances. The products of a chemical reaction may have less energy than the reactants. In some reactions, the products have a net energy less than that of the reactants. An exothermic reaction is a reaction in which energy is released in the form of heat or light. The heat released is represented by q. Energy released during a chemical reaction is chemical energy, which is sometimes called chemical potential energy.
When a substance is heated, its temperature increases. The amount of the temperature change depends on two things: the mass of the substance and the nature of the substance. The amount of heat needed to raise the temperature of a system by 1°C is its heat capacity (C). This definition does not apply to a defined mass of the substance —the heat capacity of a pool of water is obviously greater than the heat capacity of a glass of water. Specific heat (c) is the amount of heat needed to raise one gram of a substance by 1°C. The specific heat capacity of water in a pool and water in a glass are the same. Different substances have different specific heat capacities. For example, water has a high specific heat capacity compared to many common liquids, such as oil.Specific heat is an intrinsic material property, which means it does not depend on the amount of material. Heat, mass, specific heat capacity, and change in temperature relate to each other with the following equations: