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Thermodynamics (A-level only) key terms
Use these key terms for Thermodynamics (A-level only) in AQA Chemistry 7405. The page is built from approved learning objectives for this topic and links back to the wider unit, topic hub, and related revision assets.
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key terms
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Thermodynamics (A-level only)
Key terms
Born–Haber cycle
A diagrammatic representation of the stepwise formation of an ionic compound from its constituent elements, showing the enthalpy changes for each elementary process such as ionisation, electron gain, sublimation, dissociation and lattice formation.
Lattice enthalpy
The enthalpy change that occurs when gaseous ions combine to form one mole of an ionic solid; it is a measure of the strength of the ionic lattice and is calculated from the Born–Haber cycle.
lattice enthalpy
The energy change when one mole of an ionic compound is formed from its gaseous ions.
Born-Haber cycle
A thermodynamic cycle that relates the lattice enthalpy of an ionic compound to other energy changes involved in its formation.
Experimental Lattice Enthalpy
The lattice enthalpy determined through direct measurement, typically involving the enthalpy change when one mole of an ionic compound is formed from its gaseous ions.
Theoretical Lattice Enthalpy
The lattice enthalpy calculated using theoretical models based on the ionic charges and sizes of the ions involved, often derived from Coulomb's law.
lattice enthalpy
The energy change when one mole of an ionic compound is formed from its gaseous ions.
covalent character
The extent to which an ionic bond exhibits covalent characteristics, often inferred from lattice enthalpy comparisons.
entropy
A measure of the dispersal of energy or disorder in a system. In Entropy and Gibbs free energy (A-level only), entropy is used to explain explain entropy as a measure of dispersal of energy or disorder with A-Level Chemistry precision.
Gibbs free energy
A thermodynamic potential that indicates the feasibility of a reaction, calculated using the formula ΔG = ΔH - TΔS.
entropy change
The difference in entropy between the products and reactants of a reaction, indicating the degree of disorder or dispersal of energy.
standard entropy data
The entropy values of substances measured under standard conditions (298 K and 1 atm), used to calculate changes in entropy during chemical reactions.
Gibbs free energy change
The change in Gibbs free energy (ΔG) is calculated using the formula ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
Feasibility of a reaction
A reaction is considered feasible if the Gibbs free energy change (ΔG) is negative, indicating that the reaction can occur spontaneously under the given conditions.
Gibbs free energy
A thermodynamic quantity used to predict the feasibility of a reaction, calculated using the formula ΔG = ΔH - TΔS.
Feasibility
The likelihood of a reaction occurring, determined by the sign of Gibbs free energy change (ΔG); a negative ΔG indicates a feasible reaction.
feasibility
The likelihood of a reaction occurring based on Gibbs free energy calculations. In Entropy and Gibbs free energy (A-level only), feasibility is used to explain explain why feasibility does not guarantee an observable reaction rate with A-Level Chemistry precision.
reaction rate
The speed at which reactants are converted into products in a chemical reaction. In Entropy and Gibbs free energy (A-level only), reaction rate is used to explain explain why feasibility does not guarantee an observable reaction rate with A-Level Chemistry precision.
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