Thermal energy

Thermal energy ( and heat energy ), the energy stored in the disordered motion of the atoms or molecules of a substance. Is a state variable and part of the internal energy. The thermal energy is the SI unit system in joules ( unit symbol: J ) is measured.

With

• C is the specific heat capacity
• M is the mass and
• T is the absolute temperature.

A heat supply increases the average kinetic energy of molecules, and thus the thermal energy, a heat transfer reducing. Thermal energy is thus kinetic energy, but with the feature of disordered motion of many bodies, see also lattice vibration and phonon. The kinetic energy of all the molecules of the substance is equal to zero, then, because M and C are always greater than zero, the temperature at the absolute zero. Kelvin temperature scale uses this as a reference point.

If two systems with different temperatures are combined, then their temperatures equal to heat exchange. However, it goes without extra help never thermal energy from the system of lower temperature in the system of higher temperature. This empirical fact is expressed in the second law of thermodynamics. The approximation is carried out until no temperature difference between the systems occurs more and therefore the systems are in thermal equilibrium. This process is called heat transfer.

Related to the temperature

Colloquially, the thermal energy is somewhat inaccurately as " heat " or " heat energy " means, or even confused with the temperature.

In fact, for free particles, the thermal energy is proportional to the temperature:

With the Boltzmann constant.

In general, however, is the specific heat capacity is a function of temperature:

So that the thermal energy is not dependent upon the temperature in a simple proportional to:

At a phase transition even the thermal energy of the body can be changed without causing a change in temperature. An example that illustrates the relationships between heat and temperature, is a melting process. Ice has a temperature of 0 ° C, in order to melt it, to increase its thermal energy. For this heat must be supplied. However, the temperature does not rise during the melting process, since the total heat supplied to the phase transition from solid to liquid is required ( heat of fusion ).

The sometimes been called a " pressure energy " is nothing other than thermal energy. Gas molecules which are included in a vessel discharged, due to their thermal motion against the walls. This pulse is transmitted with each thrust, which can be measured as pressure.

Neutron Physics

Another word meaning thermal energy associated with free neutrons or other particles. In these cases that kinetic energy of the individual particle is meant which corresponds to the temperature of the surrounding material ( see also: thermal).

• Thermodynamics
• Form of energy