AS CHEMISTRY Unit 2 Definitions (AQA)

Definitions for unit 2 keywords.

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CHEMISTRY UNIT TWO DEFINITIONS
Activation Energy
The minimum amount of kinetic energy particles require to collide and react.
Average Bond Enthalpy
Energy needed to break one mole of bonds in the gas phase, averaged over a
number of different compounds.
Catalysts
A species that increases the rate of reaction by providing an alternative reaction
pathway with a lower activation energy. The catalyst remains chemically
unchanged at the end of the reaction.
Enthalpy Change
The heat energy involved in a reaction at constant pressure.
Hess' Law
Total enthalpy change is independent of the route taken.
Le Chatelier's Principle
If there is a change in concentration, temperature or pressure, the equilibrium will
shift in the direction that tends to oppose the change.
Standard Enthalpy of Combustion
Enthalpy change when one mole of a substance is burnt completely in oxygen in
standard states under standard conditions of temperature and pressure.
Standard Enthalpy of Formation
Enthalpy change when one mole of a compound is formed from it's elements in
their standard states under standard conditions of temperature and pressure.
Rate of Reaction
Change in concentration over a given time.

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