Magic for Learning and Revision

Join Us
Equilibria is a state of balance.


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.

It is possible to disturb equilibria in reversible reactions by changing the conditions. If you understand rates of reaction, understanding equilibria should be reasonably straightforward for you. In industrial chemistry, getting the balance right is often a compromise between the speed of reaction and the yield, as you will have seen in your studies of the Haber Process.

Firstly, let's look at an increase in temperature. In reversible reactions, if one of the reactions is exothermic and the other endothermic, the yield of products will be affected. A temperature increase will favour the endothermic reaction since there will be more energy available to be absorbed from the surroundings. So if the forward reaction is endothermic, a higher percentage of the reactants will be converted into products, and vice-versa if it is the reverse reaction that is endothermic.

Secondly, we will consider what effect an increase in concentration has on equilibria. If the concentration of the reactants is increased, that will increase the rate of the forward reaction, so more product will be made and vice-versa. Where the reaction is between gases, the equivalent of an increase in concentration is an increase in pressure. If there are fewer gas molecules on the products side than on the reactants side, the higher pressure will favour the products. As always, with equilibria, the opposite is also true.

When discussing changes to equilibria, chemists usually talk about pushing the equilibrium to the left or to the right. An equilibrium that is pushed to the right actually indicates that the forward reaction is favoured and that you will get more product; one that is pushed to the left will have less product and more reactants.

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
If a reversible reaction is exothermic in the forward direction, in the reverse direction it will be...
unknown - you cannot tell
Knowing which direction of the reversible reaction is exothermic can help you to predict what might happen when the temperature is changed
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
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
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
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
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
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
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
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
You can find more about this topic by visiting BBC Bitesize - Reversible reactions

Author:  Kate Gardiner

© Copyright 2016-2024 - Education Quizzes
Work Innovate Ltd - Design | Development | Marketing

Valid HTML5

We use cookies to make your experience of our website better.

To comply with the new e-Privacy directive, we need to ask for your consent - I agree - No thanks - Find out more