What is defined as the measure of the average kinetic energy of particles in a substance?

The concept of temperature is fundamentally connected to the average kinetic energy of the particles within a substance. Temperature is a quantitative measure that reflects how much thermal energy is present as a result of the motion of these particles. As the temperature increases, the average kinetic energy of the particles also increases, indicating that they are moving faster. This relationship is key to understanding thermal phenomena in chemistry and physics.

In contrast, heat refers to the energy that is transferred from one system to another due to a temperature difference, rather than a measure of kinetic energy in itself. Enthalpy is a state function that incorporates both the internal energy of a system and the product of its pressure and volume; it plays a critical role in heat transfer during chemical reactions but does not measure kinetic energy directly. Pressure is the force exerted by particles colliding with the walls of a container and is not a direct measure of their kinetic energy. Therefore, the correct answer highlights the specific definition of temperature as it pertains to particle motion and average kinetic energy.