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 
GibbsDuhem relation  0 = SdT  Vdp + Σ_{i}n_{i}dμ_{i} 
GibbsHelmholtz 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}  
JouleThompson 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_{j}n_{j} = mole fraction of substance i
R = gas constant