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Year 11
OCR
Foundation

Introduction to reversible chemical reactions

I can describe reversible chemical reactions, represent them using chemical equations, and give examples.

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Share activities with pupils
New
New
Year 11
OCR
Foundation

Introduction to reversible chemical reactions

I can describe reversible chemical reactions, represent them using chemical equations, and give examples.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Different types of arrows (→, ⇌) are used in chemical equations to indicate the nature of the reaction.
  2. Reversible reactions are symbolised using the double-headed arrow (⇌) in chemical equations.
  3. In a reversible reaction, both the forward and reverse reactions can occur under the right conditions.
  4. hydrated copper sulfate (blue) ⇌ anhydrous copper sulfate (white) + water
  5. ammonium chloride ⇌ ammonia + hydrogen chloride

Common misconception

Students often think that a reversible reaction will always go to completion in one direction before reversing.

Explain that in a reversible reaction, if the conditions allow it, both the forward and backward reaction can occur at the same time.

Keywords

  • Reversible reaction - A chemical reaction where the reactants form products that, in turn, react together to reform the reactants.

  • Hydrated (salt) - A salt that contains water molecules within its crystal structure, shown by a dot in its formula, e.g. hydrated copper(II) sulfate (CuSO₄·5H₂O).

  • Anhydrous (salt) - A salt that does not contain any water molecules in the crystal structure, e.g. anhydrous copper(II) sulfate (CuSO₄).

  • Double-headed arrow (⇌) - Used to show that a chemical reaction is reversible.

  • Single-headed arrow (→) - Used to show the direction of an (irreversible) chemical reaction, showing that reactants form products.

Use simple experiments to show that reversibility does not mean full completion in one direction before the reverse begins.
Teacher tip

Equipment

Test tubes, clamp and stand, ammonium chloride, hydrated copper(II) sulfate, Bunsen burners, mineral wool, delivery tube and bung, ice bath.

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.
Match the following key words to their definition.
Correct Answer:endothermic,energy is transferred from the surroundings to the reaction

energy is transferred from the surroundings to the reaction

Correct Answer:exothermic,energy is transferred from the reaction to the surroundings

energy is transferred from the reaction to the surroundings

Q2.
Which of the following statements about chemical reactions are correct?
all atomic bonds are broken before new ones are made
Correct answer: particles must collide with enough energy to react
Correct answer: reactants form products
a chemical reaction is always exothermic
Q3.
The rate of a chemical reaction is equal to the amount of product formed per unit .
Correct Answer: time
Q4.
A chemical reaction produces 0.5 g of gas in 10 seconds. Which is the correct rate of reaction?
0.5 grams
10 seconds
Correct answer: 0.05 grams per second
0.05 seconds per gram
0.05
Q5.
The rate of a reaction can be changed by varying concentration or temperature, but also by changing the of a solid reactant.
Correct Answer: surface area
Q6.
Which of the following statements about catalysts is incorrect?
a catalyst speeds up a reaction without being used up or chemically changed
catalysts are specific; different reactions require different catalysts
enzymes are biological catalysts that speed up reactions in living cells
Correct answer: reactions need catalysts to start and only take place when a catalyst is present

Exit quiz

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6 Questions

Q1.
Match the following key terms to their definition.
Correct Answer:irreversible reaction,reactants form products, and the reaction goes to completion

reactants form products, and the reaction goes to completion

Correct Answer:reversible reaction,both forward and backward reactions occur under the correct conditions

both forward and backward reactions occur under the correct conditions

Q2.
Which of the following symbols is used to indicate a reversible reaction?
→
↔
⇄
Correct answer: ⇌
Q3.
In reversible reactions, the forward and backward reactions have different energy changes. When energy is taken in from the surroundings, the reaction is called an reaction.
Correct Answer: endothermic
Q4.
True or false? In a reversible reaction, the forward reaction needs to reach completion before the backward reaction can start.
true
Correct answer: false
Q5.
The direction of reversible reactions can be influenced by changing conditions, such as temperature. By cooling a reaction down, the system will change to favour the reaction.
Correct Answer: exothermic
Q6.
Match the following key words to their definition.
Correct Answer:hydrated,contains water molecules in its crystal structure (dot in the formula)

contains water molecules in its crystal structure (dot in the formula)

Correct Answer:anhydrous,does not contain any water molecules in the crystal structure

does not contain any water molecules in the crystal structure