Difference Between Thermal Energy and Temperature

Thermal Energy vs Temperature

Thermal energy and temperature are two concepts discussed in physics. These concepts are widely used and discussed in thermodynamics and heat. The concepts of thermal energy and temperature play a very important role in fields such as heat and thermodynamics, mechanical engineering, physical chemistry, physics, astronomy, and various other fields. In this article, we are going to discuss what thermal energy and temperature are, their definitions, the applications of thermal energy and temperature, the dimensions and units of thermal energy and temperature, and finally the similarities and differences between thermal energy and temperature.

Thermal Energy

Thermal energy, which is more commonly known as heat, is a form of energy. It is measured in joules. Thermal energy is an internal energy for a given system. Thermal energy is the cause for the temperature of a system. Every system having a temperature above absolute zero has a positive thermal energy. The thermal energy occurs due to the random movements of the molecules, atoms, and electrons of the system. The atoms themselves do not contain any thermal energy, but they have kinetic energies. When these atoms collide with each other and with the walls of the system they release thermal energy as photons. Heating such a system will increase the thermal energy of the system.

Thermal energy is a form of random energy, which is not able to do work, when the whole system is considered. Higher the thermal energy of a system higher will be the randomness of the system. Thermal energy can be converted in to mechanical energy using a heat engine. In theory, thermal energy cannot be converted to mechanical energy with 100% efficiency. This is due to the universal entropy increment due to the cycle of the heat engine.


Temperature is the measureable thermal property of a system. It is measured in Kelvin, Celsius, or Fahrenheit. The SI unit for temperature measurement is Kelvin.

The thermal energy of a system is proportional to the absolute temperature of the system. If the system is at absolute zero (zero kelvin), the thermal energy of the system is also zero. However, an object having a higher temperature can carry lesser thermal energy. This is due to the reason that the thermal energy depends on the mass of the object, the heat capacity of the object, as well as the temperature of the object.

What is the difference between Temperature and Thermal Energy?

• Thermal energy is not a directly measurable quantity whereas temperature is a measurable quantity.

• The temperature of an object can take negative values depending on the unit system used to measure the temperature, but the thermal energy of a system cannot be negative.

• Temperature is measured in Kelvin whereas thermal energy is measured in Joule.

• An object can lose or gain thermal energy in a state transition without changing the temperature of the system.