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Year 11
AQA
Foundation

Chemical equilibrium

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

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New
New
Year 11
AQA
Foundation

Chemical equilibrium

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

Download all resources
Share activities with pupils

Lesson details

Key learning points

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

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.

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.

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.
Teacher tip

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 (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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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?
An image in a quiz
arrangement of particles
Correct answer: elasticity of particles
Correct answer: forces between particles
Correct answer: movement of particles

Exit quiz

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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