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# 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
 Term Function Activity coefficient γi = fi/(xifiθ) Chemical potential μi = (∂G/∂ni)T,p,nj≠i Energy U Enthalpy H = U + pV Entropy S Fugasity fi = (xi)exp{(μi - μiÞg)/RT} Gibbs (free) energy G = U + pV - TS Gibbs-Duhem relation 0 = SdT - Vdp + Σinidμi Gibbs-Helmholtz equation H = G - T(∂G/∂T)p Helmholtz energy A = U - TS Isentropic (constant heat and mass) compressibility κS = - (∂V/∂p)S/V Isothermal (constant temperature) compressibility κT = - (∂V/∂p)T/V κT - κS  = T αV2V/Cp Isobaric (constant pressure) expansivity αV= (∂V/∂T)p/V Isobaric heat capacity Cp = (∂H/∂T)p Isochoric (constant volume) heat capacity CV = (∂U/∂T)v Cp - CV = Tα2V/κT Joule-Thompson expansion μJT = (∂T/∂p)H = - {V - (∂V/∂T)p}/Cp ΦJT = (∂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 Xi = (∂X/∂ni)T,p,nj≠i Perfect (ideal) gas [symbol Þg] pV = (Σini)RT μiÞg = μiθ + RTln(xip/pθ)

Where

p = pressure
V = Volume
T = temperature
ni = amount of substance i
xi = nijnj = mole fraction of substance i
R
= gas constant

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Temperature

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Length

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Area

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Volume

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Weight

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Velocity

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Pressure

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Flow

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