Heat and Thermodynamics

The form of energy that can be transferred from points of high temperature to the points of low temperature as a result of temperature difference is called heat. The transfer of heat occurs by conduction, convection and radiation. When the temperature of system changes, its heat energy changes by an amount equal to the product of its mass, its specific heat capacity and its change in temperature. The heat of a system is the kinetic energy due to translation, rotation and vibration of its molecules. The unit of heat is joule.

Before the principles of thermodynamics were clearly established the word heat was used with various meanings, including temperature and internal energy.

The study of the interrelation between heat, work and internal energy is called thermodynamics. The thermodynamic state of a body is defined in terms of certain thermodynamic variables.

The theory is based on three laws:

The first law states that the heat absorbed by any system is equal to the work done by that system plus its internal energy:

Dq = Dw + dU

It is equivalent to the idea that heat is a form of energy and application of the law of conservation of energy.

The second law states that heat cannot pass from colder to the hotter body without any other external effect occurring.

Third law states that entropy of a substance approaches zero as its thermodynamic temperature approaches zero. The third law is the modified form of earlier Nernst heat theorem. Thermodynamics is used in study of heat energies, chemical reaction and chemical equilibrium.