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chemistry igcse acapprinted 58 · PDF 58
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• By increasing the concentration the rate of reaction increases, and vice versa.
This is because, when the concentration increases:
• Particles become more crowded together.
• The frequency of collisions increases.
(iv) Particle Size
• Particles in powdered form have a higher surface area, therefore:
• The frequency of collisions increases.
• The rate of reaction becomes faster.
• Particles in the form of lumps have a smaller surface area, therefore:
• The frequency of collisions decreases.
• The rate of reaction becomes slower.
(v) Catalysts
• A catalyst is a substance which speeds up a chemical reaction without being
used up.
By adding a catalyst the rate of reaction increases. This is because, when a
catalyst is added:
• The activation energy of the reaction is lowered, providing an alternate
pathway for the reaction.
Reversible Reactions and Equilibrium
Reversible and Irreversible Reactions.
• Reversible Reactions are reactions which can proceed in both forward and
backward directions, for example,