First law of thermodynamics

                        The first law of thermodynamics may be stated in several ways:

The increase in internal energy of a body is equal to the heat supplied to the body minus work done by the body.

For a thermodynamic cycle, the heat supplied to a closed system, minus that removed from it, equals the net work done by the system.

The increase in internal energy of a closed system for any process of interest between an initial and a final state of internal thermodynamic equilibrium is equal to the change in internal energy for a reference process consisting only of adiabatic work that goes from that initial to that final state.

More specifically, the First Law encompasses several principles:

• The law of conservation of energy.

This states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. The total energy of an isolated system remains the same.

• The concept of internal energy and its relationship to temperature.

If a system has a definite temperature, then its total energy has three distinguishable components. If it is in motion, it has kinetic energy. If it is in an externally imposed force field (e.g. gravity), it has potential energy. And it has internal energy which is the sum of the kinetic energy of microscopic motions of its constituent atoms, and of the potential energy of interactions between them. Other things being equal, the kinetic energy of microscopic motions of the constituent atoms increases as the system's temperature increases. The establishment of the concept of internal energy is the characteristic distinguishing feature of the first law of thermodynamics.

• The flow of heat is a form of energy transfer.

In other words, a quantity of heat that flows from a hot body to a cold one can be expressed as an amount of energy being transferred from the hot body to the cold one.

• Performing work is a form of energy transfer.

For example, when a machine lifts a heavy object upwards, some energy is transferred from the machine to the object. The object acquires its energy in the form of gravitational potential energy in this example.

Combining these principles leads to one traditional statement of the first law of thermodynamics: it is not possible to construct a perpetual motion machine which will continuously do work without consuming energy.