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is the study of changes in energy that accompany chemical reactions and physical changes


a device used to measure the energy as heat absorbed or released in a chemical or physical change


a measure of how hot or cold something is, specifically, a measure of the average kinetic energy of the particles in an object


the unit used to express energy: equivalent to the amount of work done by a force of 1 N acting through a distance of 1 m in the direction of the force (abbreviation J)


the energy transferred between objects that are different temperatures: energy is always transferred form higher-temperature objects to lower-temperature objects until thermal equilibrium is reached

specific heat

the quantity of heat required to raise a unit mass of homogenous material 1 K or 1C in a specified way given constant pressure and volume

enthalpy change

the amount of energy released or absorbed as heat by a system during a process at constant pressure

enthalpy of reaction

the amount of energy released or absorbed as heat during a chemical reaction

thermochemical equation

an equation that includes the quantity of energy released or absorbed as heat during the reaction as written

molar enthalpy of formation

the amount of energy as heat resulting from the formation of 1 mol of a substance at constant pressure

enthalpy of combustion

the energy released as heat by the complete combustion of a specific amount of a substance at constant pressure or constant volume

Hess's law

the overall enthalpy change in a reaction is equal to the sum of the enthalpy changes for the individual steps in the process


a measure of randomness or disorder of a system

free energy

the energy in a system that is available for work: a system's capacity todo useful work

free-energy change

the difference between the change in enthalpy, deltaH, and the product of the Kelvin temperature and the entropy change, which is defined as TdeltaS, at a constant pressure and temperature.

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