Internal energy is a measure of the total energy of all the particles in a system. It is made up of two main types of energy stores:
1. Kinetic energy – This relates to the motion of molecules and particles. For instance, as gas particles move more rapidly, their kinetic energy increases.
2. Potential energy – This is the energy an object possesses because of its position or arrangement relative to other objects.
Materials have internal energy. When a substance is heated, its internal energy increases. In contrast, when it cools, its internal energy decreases.
Heating a substance will cause particles to speed up, increasing the kinetic energy of its molecules. This is why temperature is a measure of the average kinetic energy of the particles of a substance.
However, once a substance reaches a certain temperature, adding more heat doesn’t further increase its kinetic energy.
Due to the conservation of energy, any energy transferred to the substance must be split between the kinetic and potential energy stores.
This means that adding more heat will primarily increase the substance’s potential energy. This added potential energy can break the bonds between the substance’s molecules, leading to a change in its state. Therefore, even if heat continues to be applied to the substance, its temperature remains constant.