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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

## Related Topics

• ### Thermodynamics

Work, heat and energy systems.

## Related Documents

• ### 1st Law of Thermodynamics

The First Law of Thermodynamics simply states that energy can be neither created nor destroyed (conservation of energy). Thus power generation processes and energy sources actually involve conversion of energy from one form to another, rather than creation of energy from nothing.
• ### 2nd Law of Thermodynamics

Entropy and disorder.
• ### Air - Thermophysical Properties

Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.
• ### Combustion Heat

Heat of combustion (energy content) for som common substances - with examples how to calculate heat of combustion.
• ### Dimensionless Numbers

Physical and chemical dimensionless quantities - Reynolds number, Euler, Nusselt, and Prandtl number - and many more.
• ### Heat Capacity

The amount of heat required to change the temperature of a substance by one degree.
• ### Inorganic Compounds in Water - Melting and Boiling Temperature, Density and Solubility

Physical constants for more than 280 common inorganic compounds. Density is given for the actual state at 25°C and for liquid phase at melting point temperature.
• ### Property vs. State

The concept of properties and state.
• ### Symbols Used to Denote a Chemical Reactions and Process or Condition

Explanation of symbols used as subscripts or superscripts to tell more about the type of chemical reaction, process or condition.
• ### Third Law of Thermodynamics

The entropy of a substance is zero if the absolute temperature is zero.
• ### Universal and Individual Gas Constants

The Universal and Individual Gas Constants in fluid mechanics and thermodynamics. Individual gas constants for the most common gases.
• ### WABT - Weighted Average Bed Temperature

Definition and examples of calculation of weighted average bed temperature in adiabatic reactors.
• ### Water - Thermophysical Properties

Thermal properties of water at different temperatures like density, freezing temperature, boiling temperature, latent heat of melting, latent heat of evaporation, critical temperature and more.

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## Citation

• The Engineering ToolBox (2003). Thermodynamic Terms - Functions and Relations. [online] Available at: https://www.engineeringtoolbox.com/thermodynamic-terms-d_149.html [Accessed Day Month Year].

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7.25.9

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