Key definitions for Chemistry

definitions for some of the key terms. This is a work in progress, it's not finished yet.

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  • Created by: Em
  • Created on: 06-06-10 13:21
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First ionisation enthalpy: the energy needed to remove one electron from each of one mole of
isolated gaseous atoms of an element. One mole of gaseous ions with one positive charge is formed.
The units are kJ/mol.
Spectator ions: ions not involved in the reaction
Redox Reaction: when an oxidation reaction and reduction reaction occur simultaneously
Oxidation: Loss of electrons ­ oxidation state is increased
Reduction: gain of electrons ­ oxidation state is decreased
Displacement reaction: occurs when a more reactive halogen is passed into a solution of less
reactive halide ions.
Instantaneous dipole: electron density may be unevenly distributed at any time ­ the polarity
Instantaneous ­ induced dipole: a molecule that is polar (due to instantaneous) approaches
another element; the electrons will all move to one side of the element due to charge.
Permanent ­ permanent dipole: the
slightly positive end of one element will attract the slightly negative end of another.
Stronger than instantaneous ­ induced dipole but weaker than hydrogen bonds
Electro negativity: the degree to which an atom attracts electrons - generally increases towards
top and right of periodic table.
Carbocation: positively charged carbon ­ electrophilic
Nucleophilic: have one or more lone pairs of electrons that they can donate to form new bonds.
Batch process: reactants are placed in a reaction vessel and allowed to react. Once reaction is
over, the products are removed and the vessel is cleaned and made ready for next batch.
E.g. dyes, pharmaceuticals and pesticides
Continuous process: starting materials regularly fed in at one end of the plant, product emerges
at other end.
E.g. ethene, ammonia and sulphuric acid
Variable costs: depend on amount of product manufactured
Fixed costs: same, irrespective of how much product is made
Elimination Reaction: A small molecule is removed from a larger molecule leaving an unsaturated
Enthalpy change of combustion: The energy change when one mole of a substance burns
completely in oxygen under standard conditions
Enthalpy change of formation: the energy change when one mole of a substance is formed from
its constituent elements. Both the reactants and products are in their standard state.

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