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catalyst - a substance that speeds up a chemical reaction without itself being consumed by the reaction. It works by providing an alternative route with a lower activation energy, by which the reaction can take place.

dynamic equilibrium – the stage in a reversible reaction when the rates of the forward and backward reactions are the same and the concentrations of the components of the mixture remain constant.

equilibrium constant - a value for the ratio of concentration of products to reactants at equilibrium. It is constant at a specific temperature.

Kc – the equilibrium constant given in units of concentration. For the general reaction: aA + bB <-> cC + dD
Kc is given, in terms of the equilibrium concentrations, by: Kc = [C]c[D]d / [A]a[B]b

Le Chatelier’s principle – a principle stating that if a factor affecting the position of an equilibrium is altered, the position of the equilibrium changes to oppose the effect of the change.

mole fraction – the mole fraction of a component is equal to the number of moles of the component in a mixture divided by the total number of moles.
mole fraction of A = no. moles of A / total no. moles of all components.

partial pressure – the pressure that a gas would exert if it were the only gas present. The partial pressure of a particular gas is equal to the mole fraction multiplied by the total pressure:

partial pressure - mole fraction × total pressure

the sum of all partial pressures in a mixture is equal to the total pressure.

reversible reaction - a reaction that does not go to completion. Instead, a state of dynamic equilibrium is set up, with products reforming reactants at the same rate that reactants form products.

yield – the amount of a substance produced.