The joule per mole (symbol: J·mol⁻¹ or J/mol) is the unit of

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

per

amount of substance In chemistry, the amount of substance (symbol ) in a given sample of matter is defined as a ratio () between the particle number, number of elementary entities () and the Avogadro constant (). The unit of amount of substance in the International ...

in the

International System of Units The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...

(SI), such that energy is measured in

joule The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work d ...

s, and the amount of substance is measured in moles. It is also an SI derived unit of molar thermodynamic energy defined as the energy equal to one joule in one mole of substance. For example, the

Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol is a thermodynamic potential that can be used to calculate the maximum amount of Work (thermodynamics), work, other than Work (thermodynamics)#Pressure–v ...

of a compound in the area of thermochemistry is often quantified in units of kilojoules per mole (symbol: kJ·mol⁻¹ or kJ/mol), with 1 kilojoule = 1000 joules. Physical quantities measured in J·mol⁻¹ usually describe quantities of energy transferred during phase transformations or

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

s. Division by the number of moles facilitates comparison between processes involving different quantities of material and between similar processes involving different types of materials. The precise meaning of such a quantity is dependent on the context (what substances are involved, circumstances, etc.), but the unit of measurement is used specifically to describe certain existing phenomena, such as in thermodynamics it is the unit of measurement that describes molar energy. Since there are 6.02214076 particles (atoms, molecules, ions etc.) per mole, 1 joule per mole is equal to 1 joule multiplied by 6.02214076 particles. Because of the typical order of magnitude for energy changes in chemical processes, kJ·mol⁻¹ is normally used instead of J·mol⁻¹. For example, heats of fusion and

vaporization Vaporization (or vapo(u)risation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenome ...

are usually of the order of 10 kJ·mol⁻¹, bond energies are of the order of 100 kJ·mol⁻¹, and ionization energies of the order of 1000 kJ·mol⁻¹. For this reason, it is common within the field of chemistry to quantify the enthalpy of reaction in units of kJ·mol⁻¹. Other units sometimes used to describe reaction energetics are kilocalories per mole (kcal·mol⁻¹), electron volts per particle (eV), and wavenumbers in inverse centimeters (cm⁻¹). 1 kJ·mol⁻¹ is approximately equal to 1.04 eV per particle, 0.239 kcal·mol⁻¹, or 83.6 cm⁻¹. At room temperature (25 °C, or 298.15 K) 1 kJ·mol⁻¹ is approximately equal to 2.479

k_B T

References

{{DEFAULTSORT:Joule Per Mole SI derived units Units of chemical measurement