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Equilibria is a state of balance.
Equilibria
This GCSE Chemistry quiz is all about equilibrium. The word equilibrium means something is in a state of balance. In chemistry, it refers to a situation in which the concentrations of the reactants and the products are constant. The plural is equilibria and this word refers to the study of concentrations in chemical reactions. Only reversible chemical reactions are subject to equilibria. In a non-reversible reaction, the products do not react with each other. In a reversible reaction, the products can react together to re-form the products.
There are quite a number of reversible reactions, for example, the manufacture of ammonia. During a reversible reaction, both the forwards reaction of reactants going to products AND the backwards reaction of products going to reactants are taking place at the same time. At equilibrium, the two chemical reactions are going at the same rate and so the concentrations of each substance present in the mixture remains the same.
1.
How do we represent a reversible reaction symbolically?
→
←
↓
⇌
This shows the two directions that the reaction will proceed in, both forwards and reverse. Sometimes the arrow is drawn with a larger arrow in one direction to show the predominant reaction direction
2.
What is a reversible reaction?
A reaction which will proceed in the forwards direction only
A reaction which will proceed in both forwards and backwards directions
A reaction which will proceed in the backwards direction only
A reaction which will not proceed in any direction
A good example of a reversible reaction is the formation of ammonia from hydrogen and nitrogen
3.
At equilibrium, if the rate of the forward reaction increases, the rate of the reverse reaction...
increases until it is going at the same rate as the forward reaction
decreases until both reactions are going at the same rate
carries on at a steady rate
increases to faster than the forward reaction
At equilibrium, the rate of the forward and reverse reaction are the same. To compensate for the increased rate of the forward reaction, the reverse reaction must also increase
4.
A stable equilibrium can be achieved in a...
chemical system
open system
closed system
reaction system
A closed system is one in which no reactants or products can enter or leave
5.
What effect will adding a catalyst have to the equilibrium of a system?
No effect, it just speeds up getting to the point of equilibrium
It will increase the rate of the forward reaction only
It will increase the rate of the reverse reaction only
It decreases the amount of product produced
It speeds up both the forward and reverse reactions equally
6.
One example of a reversible reaction is the Haber process. Pick the correct symbol equation for the reaction between hydrogen and nitrogen to produce ammonia in the Haber process.
N2 + 3H2 → 2NH3
N2 + 3H2 ← 2NH3
N2 + 3H2 ⇌ 2NH3
N2 + 3H2 ⇌ NH3
You should have immediately dismissed the first two answers since they don't contain the double arrow that shows this is a reversible reaction. Ammonia is an important chemical in industry and is used to manufacture nitric acid and fertilisers
7.
At equilibrium, the amount of product(s) and reactant(s) is constant. Which of the following would increase the amount of product in a reaction?
Remove the product from the reaction vessel
Add more product to the reaction vessel
Increase the temperature of the reaction mixture
Increase the pressure of the reaction vessel
If the product is removed, there will be less of the reverse reaction occurring. The forward reaction will continue, forming more of the product to replace the quantity removed to re-establish the equilibrium. Adding more of the reactants would have the same effect
8.
If a reversible reaction is exothermic in the forward direction, in the reverse direction it will be...
endothermic
exothermic
unknown - you cannot tell
slower
Knowing which direction of the reversible reaction is exothermic can help you to predict what might happen when the temperature is changed
9.
The Haber process is a reversible reaction. If the reaction were at equilibrium, hydrogen and nitrogen would be being produced as quickly as ammonia gas was being broken down. How is the forward reaction rate increased?
By removing nitrogen and hydrogen from the reaction vessel
By removing ammonia from the reaction vessel
By increasing the amount of hydrogen and nitrogen in the reaction vessel
By increasing the pressure
The system attempts to achieve equilibrium by increasing the rate of the forward reaction, i.e. by making more ammonia to replace that which has been removed
10.
At the point of equilibrium...
the rate of the forward reaction is greater than the rate of the reverse reaction
the rate of the forward reaction is slower than the rate of the reverse reaction
the rate of the forward reaction is double the rate of the reverse reaction
the rate of the forward reaction is the same as the rate of the reverse reaction
At this point there is no overall change in the amount of products or reactants
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