Chemical equilibrium KS4 | Y11 Combined science Foundation AQA | Lesson Resources

Lesson slides

Lesson details

Learning outcome

I can explain the concept of chemical equilibrium and the characteristics of a system in which equilibrium is established.

Key learning points

At equilibrium, both reactants and products are formed at the same rate.
Amounts of reactants and products remain constant at equilibrium.
Equilibrium can only occur in a closed system.

Keywords

Dynamic equilibrium - occurs in a closed system when the forward and backward reactions of a reversible chemical reaction occur at the same rate; and the concentrations of reactants and products remain constant.
Reaction rate - is the speed with which a chemical reaction takes place, measured by the amount of a reactant used or amount of product formed in a given time.
Closed system - is one in which matter cannot enter or leave the observed environment, allowing only energy transfer between the system and its surrounding environment.

Common misconception

Equilibrium can occur in an open system; no reactions occur at equilibrium; amounts of reactants and products are equal at equilibrium.

Equilibrium requires a closed system; in an open system, matter exchange disrupts balance. At equilibrium, reactions still occur but at equal rates, leading to constant amounts, not necessarily equal amounts of reactants and products.

Teacher tip

Use visuals and models (like sealed containers) to illustrate closed systems and equilibrium. Incorporate hands-on activities, such as the busy road or liquid transfer models, to demonstrate dynamic equilibrium.

Equipment

Beakers, plastic pipettes, food colouring, glass rods.

Content guidance

Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0

except where otherwise stated. See Oak's terms & conditions

(Collection 2).

Lesson video

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Worksheet

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Prior knowledge starter quiz

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6 Questions

Q1.
Physical changes are easily reversible by changing the , for example changing the state of water from ice to liquid by heating, and back to ice by cooling.

Correct Answer: conditions

Q2.
Why are some reactions reversible?

addition is more easily achieved than decomposition

Correct answer: conditions for forward and backward reactions can easily be met

dehydration is more easily achieved than hydration

Correct answer: reactants and products have comparable stability

the reaction does not involve any energy change

Q3.
If the forward reaction of a reversible reaction is exothermic, the backward reaction will be .

Correct Answer: endothermic

Q4.
To carry out the experiment with hydrated and anhydrous copper sulfate, put the steps in order:

1 - Place 5 g of powdered blue copper(II) sulfate in a test tube.

2 - Heat the copper sulfate until the colour no longer changes.

3 - Record any observations during the heating process.

4 - Allow the anhydrous copper sulfate to cool back to room temperature.

5 - Pour the collected water very slowly onto the cooled powder.

6 - Record any observations when the water is poured back onto the powder.

Q5.
How can reaction conditions be changed so that reaction rates change?

Correct answer: adding a catalyst to the reaction

changing the shape and size of glassware

Correct answer: changing the surface area of a solid reactant

Correct answer: varying the concentration of reactant

Correct answer: varying the temperature of the reaction

Q6.
Models have limitations. What does this image of the particle model NOT attempt to show?

arrangement of particles

Correct answer: elasticity of particles

Correct answer: forces between particles

Correct answer: movement of particles

Assessment exit quiz

Download exit quiz questions (PDF)

6 Questions

Q1.
Hot coffee cooling to room temperature is a reversible process. It is a rather than a chemical change.

Correct Answer: physical, physical change

Q2.
Equilibrium is a state where opposing forces or processes are balanced. Which statements MUST be true at chemical equilibrium?

Correct answer: amounts of reactions and products are constant

amounts of reactants and products are equal

Correct answer: changes in amounts of reactants and products are equal

Correct answer: reaction rates of forward and backward reaction are equal

Q3.
Dynamic equilibrium occurs in a system when forward and backward reactions occur at the same rate, and the concentrations of reactants and products remain constant.

Correct Answer: closed

Q4.
A closed system of a glass container is filled with NO$$_2$$ under conditions which allows the equilibrium with N$$_2$$O$$_4$$ to be established. Why will you never observe a colourless situation?

N$$_2$$O$$_4$$ can leave the system, which disrupts the balance of equilibrium.

N$$_2$$O$$_4$$ is a light brown gas and NO$$_2$$ is a dark brown gas.

Correct answer: There is never a full conversion of reactant molecules to product molecules.

Q5.
Match the following key terms to their definition.

Correct Answer:closed system,system where matter cannot enter/leave, but energy can be transferred

system where matter cannot enter/leave, but energy can be transferred

Correct Answer:dynamic equilibrium,opposing processes occur with equal rates; no observable changes

opposing processes occur with equal rates; no observable changes

Correct Answer:irreversible reaction,reaction where reactants form products; reaction goes to completion

reaction where reactants form products; reaction goes to completion

Correct Answer:open system,system where both matter and energy can freely enter and leave

system where both matter and energy can freely enter and leave

Correct Answer:reversible reaction,reaction where reactants form products, which revert to reactants

reaction where reactants form products, which revert to reactants

Q6.
The models of water with food colouring, or of cars entering/leaving a road, are unhelpful for the ‘dynamic’ aspect of equilibrium, as you cannot see that individual molecules are continuously .

Correct Answer: changing, changing into each other, converting, converting into each other

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Chemical equilibrium

Lesson slides

Lesson details

Learning outcome

Key learning points

Keywords

Common misconception

Teacher tip

Equipment

Content guidance

Supervision

Licence

Lesson video

Worksheet

Prior knowledge starter quiz

6 Questions

Q1.Physical changes are easily reversible by changing the , for example changing the state of water from ice to liquid by heating, and back to ice by cooling.

Q2.Why are some reactions reversible?

Q3.If the forward reaction of a reversible reaction is exothermic, the backward reaction will be .

Q4.To carry out the experiment with hydrated and anhydrous copper sulfate, put the steps in order:

Q5.How can reaction conditions be changed so that reaction rates change?

Q6.Models have limitations. What does this image of the particle model NOT attempt to show?

Assessment exit quiz

6 Questions

Q1.Hot coffee cooling to room temperature is a reversible process. It is a rather than a chemical change.

Q2.Equilibrium is a state where opposing forces or processes are balanced. Which statements MUST be true at chemical equilibrium?

Q3.Dynamic equilibrium occurs in a system when forward and backward reactions occur at the same rate, and the concentrations of reactants and products remain constant.

Q4.A closed system of a glass container is filled with NO$$_2$$ under conditions which allows the equilibrium with N$$_2$$O$$_4$$ to be established. Why will you never observe a colourless situation?

Q5.Match the following key terms to their definition.

Q6.The models of water with food colouring, or of cars entering/leaving a road, are unhelpful for the ‘dynamic’ aspect of equilibrium, as you cannot see that individual molecules are continuously .

Additional material

How to plan a lesson using our resources

Q1.
Physical changes are easily reversible by changing the , for example changing the state of water from ice to liquid by heating, and back to ice by cooling.

Q2.
Why are some reactions reversible?

Q3.
If the forward reaction of a reversible reaction is exothermic, the backward reaction will be .

Q4.
To carry out the experiment with hydrated and anhydrous copper sulfate, put the steps in order:

Q5.
How can reaction conditions be changed so that reaction rates change?

Q6.
Models have limitations. What does this image of the particle model NOT attempt to show?

Q1.
Hot coffee cooling to room temperature is a reversible process. It is a rather than a chemical change.

Q2.
Equilibrium is a state where opposing forces or processes are balanced. Which statements MUST be true at chemical equilibrium?

Q3.
Dynamic equilibrium occurs in a system when forward and backward reactions occur at the same rate, and the concentrations of reactants and products remain constant.

Q4.
A closed system of a glass container is filled with NO$$_2$$ under conditions which allows the equilibrium with N$$_2$$O$$_4$$ to be established. Why will you never observe a colourless situation?

Q5.
Match the following key terms to their definition.

Q6.
The models of water with food colouring, or of cars entering/leaving a road, are unhelpful for the ‘dynamic’ aspect of equilibrium, as you cannot see that individual molecules are continuously .