# Thermodynamic Terms, Functions and Relations

## Common thermodynamic terms and functions - potential energy, kinetic energy, thermal or internal energy, chemical energy, nuclear energy and more

**Chemical energy -**is related to the relationships between molecules in chemical compounds. When chemicals react with each other, they may give off heat (exothermic reaction) or require heat (endothermic reaction)**Electric energy -**is related to electrons moving through a conductor**Energy -**can be reduced to the concepts of heat and work and can be found in various forms: potential energy, kinetic energy, thermal or internal energy, chemical energy, and nuclear energy**Enthalpy -**is a term with energy units that combines internal energy with a pressure/volume or flow work term**Entropy -**is a property of matter that measures the degree of randomization or disorder. The natural state is for entropy to be produced by all processes**Heat -**is energy in motion from one region to an other as a result of temperature difference**Internal energy -**has to do with activity within the molecular structure and is typically observed with temperature measurement**Kinetic energy -**is the energy of motion and is proportional to the square of the velocity as well to the mass of the moving body**Nuclear energy -**is related to the energy of atomic relationships between the fundamental particles. Nuclear fission and fusion are reactions which release nuclear energy**Potential energy -**is the energy of location or position of a mass in a force field**Property**- is a measurable characteristic of a system or substance. Temperature, density, pressure etc**Specific Heat**- The specific heat is the amount of heat required to change a unit mass (or unit quantity, such as mole) of a substance by one degree in temperature**Temperature -**is a term used to quantify the difference between warm and cold level of internal energy of a substance**Work -**is an energy form which can be equated to the rising of a weight as moving a mass in a force field or moving a liquid against a resisting force

See also Symbols Used to Denote a Chemical Reaction, Process or Condition

Term | Function |

Activity coefficient | γi = f_{i/}(x_{i}f_{i}^{θ}) |

Chemical potential | μ_{i} = (∂G/∂n_{i})_{T,p,nj≠i} |

Energy | U |

Enthalpy | H = U + pV |

Entropy | S |

Fugasity | f_{i} = (x_{i})exp{(μ_{i} - μ_{i}^{Þg})/RT} |

Gibbs (free) energy | G = U + pV - TS |

Gibbs-Duhem relation | 0 = SdT - Vdp + Σd_{i}n_{i}μ_{i} |

Gibbs-Helmholtz equation | H = G - T(∂G/∂T)_{p} |

Helmholtz energy | A = U - TS |

Isentropic (constant heat and mass) compressibility | κ_{S }= - (∂V/∂p)_{S}/V |

Isothermal (constant temperature) compressibility | κ_{T }= - (∂V/∂p)_{T}/V |

κ_{T }- κ_{S} = T α_{V}^{2}V/C_{p} | |

Isobaric (constant pressure) expansivity | α_{V}= (∂V/∂T)_{p}/V |

Isobaric heat capacity | C_{p} = (∂H/∂T)_{p} |

Isochoric (constant volume) heat capacity | C_{V} = (∂U/∂T)_{v} |

C_{p} - C_{V }= Tα^{2}V/κ_{T} | |

Joule-Thompson expansion | μ_{JT }= (∂T/∂p)_{H} = - {V - (∂V/∂T)_{p}}/C_{p} |

Φ_{JT} = (∂H/∂p)_{T} = V - T(∂V/∂T)_{p} | |

Maxwell relations | (∂S/∂p)_{T} = - (∂V/∂p)_{p} |

(∂S/∂V)_{T} = - (∂p/∂T)_{V} | |

Partial molar quantity | X_{i} = (∂X/∂n_{i})_{T,p,nj≠i} |

Perfect (ideal) gas [symbol ^{Þg}] | pV = (Σ_{i}n_{i})RT |

μ_{i}^{Þg} = μ_{i}^{θ} + RTln(x_{i}p/p^{θ}) |

Where

*p* = pressure*V* = Volume*T* = temperature*n _{i}* = amount of substance

*i*

*x*=

_{i}*n*

_{i}

*/Σ*= mole fraction of substance

_{j}n_{j}*i*

R= gas constant

R