**The average kinetic energy of the particles of a substance is determined by the temperature of the medium, using the equation for an ideal gas.** If the temperature is unknown, then the average speed and mass of the particles are utilized to determine the average kinetic energy.

Use the Maxwell-Boltzmann velocity distribution equation to calculate the average speed of the particles in a substance. Then, combine that information with the ideal gas law to calculate the average kinetic energy of a group of particles. However, there are certain assumptions, as all the energy is confined to translational motion. Internal energy, resulting from vibrational and rotational motion, is also discounted.