We know that particles react together when they bump into each other with enough energy (Collision theory). Up until know we have only looked at reactions that can only go in 1 direction. Once a match is struck it cannot reform, once a cake is baked you cannot go back to the original ingredients – These are irreversible reactions.
Now we look at reversible reactions – reactions that can go back to their starting materials.
You can predict what will happen in a reaction if you alter the conditions. This is known as Le Chatelier’s Principle.
If the concentration of a reactant is increased (A or B), more products will be formed until equilibrium is reached again. If the concentration of a product is decreased (C or D), more reactants will react until equilibrium is reached again.
If the temperature of a reaction is increased (heated) the reaction move in the endothermic reaction (more C & D made). If the temperature of a reaction decreases (cooled) the reaction moves in the exothermic directions (more A & B made)
If pressure is increased the reaction moves to where there are fewest gas molecules (A & B). If the pressure decreases it moves towards where there are more gas molecules (C & D)
BBC Bitesize – Reversible Reactions
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