How concentration, temperature and pressure shift an equilibrium, and how to predict the direction using Le Chateliers principle. Higher tier content.
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1.State Le Chateliers principle.
If a change is made to a system at equilibrium, the position of equilibrium shifts to counteract that change.
2.What happens if you increase the concentration of a reactant?
The equilibrium shifts to the right, forming more products, to use up the extra reactant.
3.What happens if you increase the concentration of a product?
The equilibrium shifts to the left, forming more reactants.
4.What happens if you remove a product as it forms?
The equilibrium shifts to the right to replace it, which increases the yield.
5.Why do industries often remove the product continuously?
It keeps pulling the equilibrium to the right, so more reactant is converted overall.
6.What happens to equilibrium if temperature is increased?
It shifts in the endothermic direction, to take in the extra energy.
7.What happens to equilibrium if temperature is decreased?
It shifts in the exothermic direction, to release energy.
8.The forward reaction is exothermic. What does raising the temperature do to the yield?
It decreases the yield, because the equilibrium shifts backwards in the endothermic direction.
9.The forward reaction is endothermic. What does raising the temperature do to the yield?
It increases the yield, because the equilibrium shifts forwards.
10.When does pressure affect an equilibrium?
Only when there are gases involved, and only when the number of gas molecules differs between the two sides.
11.What happens if pressure is increased?
The equilibrium shifts towards the side with fewer gas molecules.
12.What happens if pressure is decreased?
The equilibrium shifts towards the side with more gas molecules.
13.In N2 + 3H2 gives 2NH3, which side has fewer molecules?
The right, with 2 molecules compared with 4 on the left.
14.What does increasing pressure do to the yield of ammonia?
It increases it, because the equilibrium shifts to the right where there are fewer gas molecules.
15.What if both sides have the same number of gas molecules?
Changing the pressure has no effect on the position of equilibrium.
16.Why is a compromise temperature used in industry?
A lower temperature may give a better yield but the reaction is too slow, so a middle value balances yield against rate.
17.Why is a compromise pressure used in industry?
Very high pressure improves yield but the equipment is expensive to build and dangerous to run, so a middle value is chosen.
18.Does a catalyst shift the position of equilibrium?
No. It only affects how quickly equilibrium is reached.
19.How do you decide which way an equilibrium shifts?
Work out what change has been made, then identify which direction opposes it.
20.An exothermic forward reaction is cooled. Which way does equilibrium shift?
To the right, in the exothermic direction, to release energy and oppose the cooling.
21.Adding more of a gaseous reactant. Which way does equilibrium shift?
To the right, to use up the added reactant.
22.Why does shifting the equilibrium not change the reaction itself?
The same reaction is happening. Only the balance between the forward and reverse rates has changed.
23.Why is the yield of a reversible reaction always less than 100 per cent?
At equilibrium some product is always converting back, so the reactants are never fully converted.
24.Give the two things a chemical engineer balances when choosing conditions.
The yield at equilibrium and the rate at which equilibrium is reached, alongside the cost of the equipment and energy.
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