Editing Exact differential (section)

==== Thermodynamic state function ====
In [[thermodynamics]], when <math>dQ</math> is exact, the function <math>Q</math> is a [[state function]] of the system: a [[Function (mathematics)|mathematical function]] which depends solely on the current [[Thermodynamic equilibrium|equilibrium state]], not on the path taken to reach that state. [[Internal energy]] <math>U</math>, [[Entropy]] <math>S</math>, [[Enthalpy]] <math>H</math>, [[Helmholtz free energy]] <math>A</math>, and [[Gibbs free energy]] <math>G</math> are [[state function]]s. Generally, neither [[Work (thermodynamics)|work]] <math>W</math> nor [[heat]] <math>Q</math> is a state function. (Note: <math>Q</math> is commonly used to represent heat in physics. It should not be confused with the use earlier in this article as the parameter of an exact differential.)