Thermodynamic variable

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In thermodynamics, state variables, state parameters or thermodynamic variables describe the momentary condition of a system. Regardless of the path by which a system goes from one state to another — i.e., the sequence of intermediate states — the total change in any state variable will be the same. This means that the incremental changes in such variables are exact differentials. Below are some examples of state variables:

• Density (ρ)
• Energy (E)
• Helmholtz free energy (A)
• Gibbs free energy (G)
• Enthalpy (H)
• Internal energy (U)
• Mass (m)
• Pressure (P)
• Entropy (S)
• Temperature (T)
• Volume (V)
• The amounts of each of the chemical components { n_i }, expressed as numbers of moles or molecules