Topic 4.13-4.17 - Reversible reactions and equilibria
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Explain reversible reactions
In reversible reactions, both the forwards and backwards reactions can occur under the right conditions. the ⇌ symbol is used to show that a reaction is reversible
Explain what is meant by dynamic equilibrium
Once the forward and backward reaction has reached a dynamic equilibrium the concentrations of reactants and products remain constant. If this is disturbed by changing conditions the equilibrium position changes to counteract the change
Describe the formation of ammonia
It is a reversible reaction between Nitrogen (extracted from the air) and hydrogen (obtained from natural gas) and it can reach a dynamic equilibrium.
What is the equation for The Haber Process?
N₂+3H₂ ⇌ 2NH₃
Recall the conditions for The Haber Process
-A temperature of 450℃ -Pressure 200 atmospheres -An iron catalyst The purified gases are passed over a catalyst of iron at this temperature and pressure.
How is a dynamic equilibrium affected by a change in temperature?
When the temperature is higher, equilibrium is reached faster. Particles have more energy so there are more frequent collisions. Equilibrium yield decreases on the forward reaction because higher temperatures favour the endothermic reaction. If temperature is increased, the equilibrium moves in the direction of the endothermic reaction. It absorbs heat from the surroundings and the temperature of the surroundings will decrease. If temperature is decreased the equilibrium moves in the direction of the exothermic reaction. In The Haber Process the forwards reaction is exothermic and the backwards reaction is endothermic.
How is a dynamic equilibrium affected by a change in pressure?
When pressure is increased, the rate of attainment of equilibrium is increased. The equilibrium yield increases as the equilibrium shifts to favour the forward reaction and there is a decrease in the number of molecules.
How is a dynamic equilibrium affected by a change in concentration?
If the concentration of reactants is increased the position of equilibrium shifts towards the product (right) so more product is produced until equilibrium is reached again. If the concentration of products is increased the position of the equilibrium shifts towards the reactants (left) so more reactant is produced until equilibrium is reached again.
How is a dynamic equilibrium equation effected by the addition of an iron catalyst?
The rate of attainment of equilibrium increases. The equilibrium yield does not change. It does not effect the equilibrium position.