# ABJK ENTROPY

 Function of the state of a thermodynamic system whose change in any differential reversible process is equal to the heat absorbed by the system from its surroundings divided by the absolute temperature of the system. Also known as thermal charge.

## Related Terms

A process in which the temperature of a system is reduced without any heat being exchanged between the system and its surroundings.

### CARNOT'S THEOREM

1. The theorem that all Carnot engines operating between two given temperatures have the same efficiency, and no cyclic heat engine operating between two given temperatures is more efficient than a Carnot engine. 2. The theorem that any system has two properties, the thermodynamic temperature T and the entropy S, such that the amount of heat exchanged in an infinitesimal reversible process is given by d

### ONSAGER RECIPROCAL RELATIONS

A set of conditions which state that the matrix, whose elements express various fluxes of a system (such as diffusion and heat conduction) as linear functions of the various conjugate affinities (such as mass and temperature gradients) for systems close to equilibrium, is symmetric when certain definitions are chosen for these fluxes and affinities.

### NERNST-SIMON STATEMENT OF THE THIRD LAW OF THERMODYNAMICS

The statement that the change in entropy which occurs when a homogeneous system undergoes an isothermal reversible process approaches zero as the temperature approaches absolute zero.

### HEAT CAPACITY

The quantity of heat required to raise a system one degree in temperature in a specified way, usually at constant pressure or constant volume. Also known as thermal capacity.

All warm bodies emit light (electromagnetic radiation, mostly infrared). When this radiation is absorbed or emitted by a body, heat is transferred and termed 'heat transfer by radiation'. Such heat transfer requires a line of sight (view factor) and is proportional to the fourth power of the absolute temperature difference between bodies and the emissivity of the bodies.

### CARNOT-CLAUSIUS EQUATION

For any system executing a closed cycle of reversible changes, the integral over the cycle of the infinitesimal amount of heat transferred to the system divided by its temperature equals 0. Also 88 known as Clausius theorem.

### LINEAR REGULATOR PROBLEM

A type of optimal control problem in which the system to be controlled is described by linear differential equations and the performance index to be minimized is the integral of a quadratic function of the system state and control functions. Also known as optimal regulator problem; regulator problem.

### HEAT ENGINE

1. A machine that converts heat into work (mechanical energy). 2. A thermodynamic system which undergoes a cyclic process during which a positive amount of work is done by the system; some heat flows into the system and a smaller amount flows out in each cycle.

### LATENT HEAT

The heat required to cause a change in state of a substance from solid to liquid (latent heat of fusion) or from liquid to vapor (latent heat of vaporization). These phase changes occur without change of temperature at the melting point and boiling point, respectively.

### Related questions

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