Statement of the equation. In mathematics, if given an open subset U of R n and a subinterval I of R, one says that a function u : U × I → R is a solution of the heat equation if = + +, where (x 1, …, x n, t) denotes a general point of the domain. It is typical to refer to t as "time" and x 1, …, x n as "spatial variables," even in abstract contexts where these phrases fail to have ...

Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system.The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential, designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure …