Internal energy

Internal energy is a fundamental concept in thermodynamics, a branch of physics that deals with heat and temperature and their relation to energy and work. It is the energy associated with the random, disordered motion of molecules. It is separated in scale from the macroscopic ordered energy associated with moving objects; it refers to the invisible microscopic energy on the atomic and molecular scale.

Definition

The internal energy of a system in thermodynamics is the energy contained within the system. It is the energy necessary to create the system. It includes kinetic energy of motion, potential energy of configuration, and energy of the interactions among the particles of the system.

Measurement

The internal energy of a system can be measured or calculated from the properties of the substances that make up the system, such as temperature, pressure, and volume. The exact amount of internal energy possessed by a system depends on the types of particles in the system, the nature of the interactions between them, and the conditions under which the system is held.

Changes in Internal Energy

Changes in the internal energy of a system can occur through the transfer of energy in the form of heat or work. This is expressed in the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Applications

Internal energy is a key concept in the design and analysis of heat engines, refrigerators, and heat pumps. It is also important in understanding natural phenomena such as the behavior of gases and the conduction of heat through materials.

See also

• Thermodynamics
• Heat
• Work (physics)
• First law of thermodynamics
• Heat engine
• Refrigerator
• Heat pump