# Temperature and Heat

Temperature is a number that is related to the average kinetic energy of the molecules of a substance. If temperature is measured in Kelvin degrees, then this number is directly proportional to the average kinetic energy of the molecules.

Heat is a measurement of the total energy in a substance. That total energy is made up of not only the kinetic energies of the molecules of the substance, but total energy is also made up of the potential energies of the molecules.

So, temperature is not energy. It is, however, a number that relates to one type of energy possessed by the molecules of a substance. Temperature directly relates to the kinetic energy of the molecules. The molecules have another type of energy besides kinetic; they have potential energy, also. Temperature readings do not tell you anything directly about this potential energy.

Temperature can be measured in a variety of units. If you measure it in degrees Kelvin, then the temperature value is directly proportional to the average kinetic energy of the molecules in the substance. Notice we did not say that temperature is the kinetic energy. We said it is a number, if in degrees Kelvin, it is proportional to the average kinetic energies of the molecules; that is, if you double the Kelvin temperature of a substance, you double the average kinetic energy of its molecules.