How is temperature defined in the context of chemistry?

Temperature in the context of chemistry is defined as a measure of the average kinetic energy of the particles in a substance. This concept is fundamental because it provides insight into how particles behave at a microscopic level. As the temperature of a substance increases, the average kinetic energy of its particles also increases, leading to greater movement and often resulting in changes of state, such as melting or boiling.

This definition helps explain various phenomena, such as why gases expand when heated or why increasing temperature can accelerate chemical reactions. The relationship between temperature and the kinetic energy of particles underscores the importance of temperature in thermal dynamics and in the study of reactions. In contrast, other options do not accurately capture this relationship: density is not directly related to temperature, a fixed value for a substance does not vary with external conditions, and total energy encompasses both kinetic and potential energies, which extends beyond just temperature.