Summary
Summary GCSE Combined Science Chemistry - equilibrium
Le Chatelier's principle
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If a system is at equilibrium and a change is made to the conditions, thesystem responds to counteract the change.
Effect of temperature in equilibrium
• if the temperature is increased, the position of equilibrium moves in
the direction of the endothermic reaction
• if the temperature is reduced, the position of equilibrium moves in the
direction of the exothermic reaction
This is the reaction of carbon monoxide with hydrogen, to produce methanol.
CO(g)+2H 2(g)~CH3 0H(g)
The forward reaction is exothermic (it gives off heat), so the backward reaction
is endoth ermic (takes in heat).
if the temperature is increased, the position of equilibrium moves to the left. As
a result, less methanol is present in the equilibrium mixture.
On the other hand, lowering the temperature means the position of equilibrium
moves to the right, and more methanol is produced.
Effect of pressure in an equilibrium mixture of gases
If the pressure is increased, the position of equilibrium moves in the direction
of the gas with fewer molecules.
If we reduce the pressure, the position of equilibrium moves in the direction of
the gas with more molecules
If the numbe r of molecules are the same, change in pressure has no effect of
equilibrium, but the forward and reverse reactions will speed up
This is the reaction of carbon monoxide with hydrogen, to produce methanol:
CO(g)+2H2(g)~ CH30H(g)
On the left, there are 3 moles of gas (1 + 2), but on the right there is only 1.
Therefore, if the pressure is increased, the position of equilibrium will move to
the right and more methanol will be produced.
Reduc ing the pressure will cause the position of equilibrium to move to the
left, so the equilibrium mixture will contain less methanol.
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