Term | Definition |
calorimeter | An insulated container in which a thermometer detects the temperature change that occurs during a chemical reaction to calculate the transfer of thermal energy. |
enthalpy (H) | The energy content of a thermodynamic system at a constant pressure. |
enthalpy of reaction | The change in enthalpy that occurs during a reaction. It is equal to the difference between the enthalpy of the products and the enthalpy of the reactants. |
entropy | The measure of the dispersal of energy in a system; the net decrease of usable energy in a system for a given temperature and quantity of matter. |
free energy (G) | A substance's ability to do work, involving both the enthalpy and entropy of a substance; also called Gibbs free energy. |
free-energy change | The difference between the free energy of the products and the free energy of the reactants; △G = △H - t△S. If △G is negative for a process, the process is energetically favorable, or spontaneous. |
Hess's law | The law that the enthalpy change of a reaction equals the sum of the enthalpy changes for each step of the reaction. |
latent heat | The flow of thermal energy that produces a phase change while no temperature change is observed. |
molar enthalphy of fusion | The quantity of thermal energy required to melt one mole of a solid to a liquid with no temperature change; also called the heat of fusion. It is usually expressed in units of kilojoules per mole. |
molar enthalpy of vaporization | The quantity of thermal energy required to convert one mole of a liquid at its boiling point to its vapor at the same temperature; also called the heat of vaporization. It is usually expressed in units of kilojoules per mole. |
sensible heat | Thermal energy that, when applied to a substance, produces a temperature change in the substance. |
specific heat | The amount of thermal energy required to raise the temperature of 1 g of a substance by 1 °C. |
standard molar enthalpy of combustion | The energy released as heat by the complete burning of one mole of a substance at standard conditions. |
standard molar enthalpy of formation | The enthalpy change for the reaction that produces one mole of a compound in its standard state from its elements in their standard states; also called the heat of formation. |
standard state | In thermodynamics, 25 °C (298 K) and 1 atm of pressure. |
thermochemical equation | A chemical equation that shows the reactants, products, and amount of energy that is released or absorbed as heat. |
thermochemistry | The branch of science that studies the transfer of energy during chemical reactions or phase changes. |