Some Key Definitions F325_OCR Chemistry

includes hess cycle definitions, entropy definitions and enthalpy definitions.

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  • Created by: Beth Low
  • Created on: 24-01-12 21:03
Preview of Some Key Definitions F325_OCR Chemistry

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Chemistry Definitions
A Buffer Solution: is a mixture of a weak acid and its conjugate base that minimises the change in pH
on addition of small amounts of acid or base
The Equivalence Point: is when a volume of one solution has reacted with the same volume of a
second solution.
The End Point: is a point at which equal concentrations of the weak acid and conjugate base forms
of the indicator exist.
Entropy: is the quantitative measure of the degree of disorder in a system.
Enthalpy change of hydration: is the enthalpy change that accompanies the reaction when one mole
of isolated gaseous ions dissolves in water forming one mole of aqueous ions under o.
Enthalpy change of solution: is the enthalpy change that accompanies the reaction when one mole
of a compound is completely dissolved in water under o.
Enthalpy change of neutralisation: is the enthalpy change that accompanies the neutralisation of an
aqueous acid by and aqueous base to form one mole of water under o.
Hess Cycle Definitions
Lattice Enthalpy: is the enthalpy change that accompanies the formation of one mole of an ionic
compound from its gaseous ions under o.
Enthalpy change of formation: is the enthalpy change that accompanies the reaction when one mole
of a compound is formed from its constituent elements under o.
Enthalpy change of atomisation: is the enthalpy change that accompanies the reaction when one
mole of gaseous atoms forms the element in its standard state.
Ionisation enthalpy: is the enthalpy change that occurs when one electron from every atom in one
mole of free gaseous ions to form one mole of unipositive ions under o. (REFERENCE WHAT IOIN IS
CREATED i.e. 1+)
Electron affinity: is the enthalpy change that accompanies the addition of one electron to every
atom in one mole of gaseous atoms to form one mole of uninegative ions under o. (REFERENCE
WHAT IOIN IS CREATED i.e. 1)
Hess's Law: states that if any reaction can take place by more than one route and the initial and
final conditions are the same, the total enthalpy is the same for every route.

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