In what and how is heat measured



Thermal energy is the energy that is stored in the disordered movement of the atoms or molecules of a substance. In the SI system of units, it is measured in joules (unit symbol: J) and is part of the internal energy. Colloquially, it is somewhat imprecisely referred to as “heat” or “thermal energy”, or it is confused with temperature.

The thermal energy E.th of a substance is defined as

in which T the absolute temperature, m the crowd and c is the specific heat capacity.

A supply of heat increases the mean kinetic energy of the molecules and thus the thermal energy, a heat dissipation reduces it. Thermal energy is therefore kinetic energy, but with the characteristic of disordered Move many Body. If the kinetic energy of all molecules of a substance is zero, then there is m and c are always greater than zero, its temperature is at absolute zero. The Kelvin temperature scale uses this as a reference point.

If two systems with different temperatures come together, their temperatures equalize through heat exchange. In doing so, however, thermal energy never passes from the system of lower temperature to the system of higher temperature without additional help (this fact of experience is expressed in the Second Law of Thermodynamics). The adjustment takes place until there is no longer a temperature difference between the systems and the systems are therefore in thermal equilibrium. This process is called heat transfer.

Colloquially, heat and thermal energy are often confused with temperature. An example that illustrates the relationship between heat and temperature is a melting process. If you have ice with a temperature of 0 ° C, you have to increase its thermal energy in order to melt it. You have to warmth respectively. The temperature however, increases during the melting process Not because all the heat supplied is required for the phase transition from solid to liquid (heat of fusion).

An explanation of the formal and conceptual difference between heat and thermal energy (comparable to the difference between work and mechanical energy) can be found under thermal energy.

Has a slightly different word meaning thermal energy in connection with free neutrons or other particles. In these cases the kinetic energy is des Single particle meant, which corresponds to the temperature of the substance (see also thermal).

Category: Thermodynamics