AQA Chemistry A-Level Definitions

Question	Answer
First Ionisation Energy	The energy needed to remove 1 mole of electrons from 1 mole of atoms in the gaseous state
Relative Atomic Mass	The ratio of the average mass of one atom relative to 1/12 of the mass of an atom of carbon-12
Relative Molecular Mass	The ratio of the average mass of a molecule relative to 1/12 of the mass of an atom of carbon-12
Relative Formula Mass	The ratio of the average mass of an entity relative to 1/12 of an atom of carbon-12
Standard Enthalpy of Formation	The enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions (298K, 101kPa)
Standard enthalpy of combustion	The enthalpy change when one mole of a substance undergoes complete combustion with oxygen under standard conditions (298K, 101kPa)
Mean Bond Enthalpy	The average value of the dissociation enthalpy for a given type of bond taken from a range of different compounds
Activation Energy	The minimum amount of energy needed for a reaction to take place (for the bonds of the reactants to break and reassembling the atoms into the products); the enthalpy difference between the reactants and their transitionary state
Structural Isomer	The same molecular formula but different structural formula
Stereoisomer	The same structural formula but different spatial arrangements of atoms/groups/bonds

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	Created by Joseph Tedds about 8 years ago