F325 enthalpy and entropy

Average bond enthalpy
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.
Bond dissociation enthalpy
The enthalpy change that takes place when breaking by homolytic fission 1?mol of a given bond in the molecules of a gaseous species.
(First) electron affinity
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.
(Second) electron affinity
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.
Electron shielding
The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer shell electrons.
Endothermic
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 (?H +ve).
(Standard) enthalpy change of atomisation
The enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.
(Standard) enthalpy change of combustion,
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.
(Standard) enthalpy change of formation,
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.
(Standard) enthalpy change of hydration
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.
(Standard) enthalpy change of neutralisation,
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.
(Standard) enthalpy change of reaction,
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.
(Standard) enthalpy change of solution
The enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.
Enthalpy cycle
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.
Enthalpy profile diagram
A diagram for a reaction to compares the enthalpy of the reactants with the enthalpy of the products.
Enthalpy, H
The heat content that is stored in a chemical system.
Entropy, S
The quantitative measure of the degree of disorder in a system.
(Standard) entropy change of reaction,
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.
Exothermic
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (?H –ve).
Free energy change, ?G
The balance between enthalpy, entropy and temperature for a process: ?G = ?H – T?S. A process can take place spontaneously when ?G < 0.
Giant ionic lattice
A three-dimensional structure of oppositely charged ions, bonded together by strong ionic bonds.
Hess’s Law
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.
(First) ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.
(Second) ionisation energy
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.
Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
Standard conditions
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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