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According to energy conservation and energy being a state function that does not change over a full cycle, the work from a heat engine over a full cycle is equal to the net heat, i.e. the sum of the heat put into the system at high temperature, q H > 0, and the waste heat given off at the low temperature, q C < 0. [93]
The molar heat capacity is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the specific heat capacity, often called simply specific heat, is the heat capacity per unit mass of a material. Heat capacity is a physical property of a substance, which means that it depends on the state and properties of the substance under ...
Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 [2] which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."
According to the second law, in a reversible heat transfer, an element of heat transferred, , is the product of the temperature (), both of the system and of the sources or destination of the heat, with the increment of the system's conjugate variable, its entropy (): [1]
The above derivation uses the first and second laws of thermodynamics. The first law of thermodynamics is essentially a definition of heat, i.e. heat is the change in the internal energy of a system that is not caused by a change of the external parameters of the system.
Thermal conduction is the diffusion of thermal energy (heat) within one material or between materials in contact. The higher temperature object has molecules with more kinetic energy; collisions between molecules distributes this kinetic energy until an object has the same kinetic energy throughout.
Thermal physics, generally speaking, is the study of the statistical nature of physical systems from an energetic perspective. Starting with the basics of heat and temperature, thermal physics analyzes the first law of thermodynamics and second law of thermodynamics from the statistical perspective, in terms of the number of microstates corresponding to a given macrostate.
To explain this definition, consider a reversible Carnot cycle engine, where is the amount of heat energy transferred into the system, is the heat leaving the system, is the work done by the system (), is the temperature of the hot reservoir in Celsius, and is the temperature of the cold reservoir in Celsius.