Term
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Definition
| The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species. |
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Term
| Bond dissociation enthalpy |
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Definition
| The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species. |
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Term
| (First) electron affinity |
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Definition
| The enthalpy change required to add one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1– ions. |
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Term
| (Second) electron affinity |
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Definition
| The enthalpy change required to add one electron to each ion in one mole of gaseous 1– ions to form one mole of gaseous 2– ions. |
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Term
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Definition
| The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer shell electrons. |
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Term
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Definition
| A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (ΔH +ve). |
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Term
| (Standard) enthalpy change of atomisation |
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Definition
| The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state. |
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Term
| (Standard) enthalpy change of combustion, |
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Definition
| The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states. |
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Term
| (Standard) enthalpy change of formation, |
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Definition
| The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions. |
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Term
| (Standard) enthalpy change of hydration |
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Definition
| The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water, forming one mole of aqueous ions, under standard conditions. |
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Term
| (Standard) enthalpy change of neutralisation, |
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Definition
| The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H2O(l), under standard conditions. |
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Term
| (Standard) enthalpy change of reaction, |
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Definition
| The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states. |
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Term
| (Standard) enthalpy change of solution |
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Definition
| The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions. |
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Term
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Definition
| A diagram showing alternative routes between reactants and products that allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’s law. |
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Term
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Definition
| A diagram for a reaction to compares the enthalpy of the reactants with the enthalpy of the products. |
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Term
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Definition
| The heat content that is stored in a chemical system. |
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Term
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Definition
| The quantitative measure of the degree of disorder in a system. |
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Term
| (Standard) entropy change of reaction, |
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Definition
| The entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states. |
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Term
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Definition
| A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (ΔH –ve). |
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Term
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Definition
| The balance between enthalpy, entropy and temperature for a process: ΔG = ΔH – TΔS. A process can take place spontaneously when ΔG < 0. |
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Term
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Definition
| A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds. |
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Term
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Definition
| If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route. |
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Term
| (First) ionisation energy |
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Definition
| The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. |
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Term
| (Second) ionisation energy |
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Definition
| The energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions. |
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Term
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Definition
| The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions. |
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Term
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Definition
| A pressure of 100 kPa (1 atmosphere), a stated temperature, usually 298 K (25 °C) and a concentration of 1 mol dm–3 (for reactions with aqueous solutions). |
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