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OCR GCSE Combined Science

Topic questions Energy changes Exothermic & endothermic reactions

Exothermic & endothermic reactions

9 questions · 81 marks · about 1.5 hours

Exothermic and endothermic reactions questions

TopicExothermic & endothermic reactions

OCR J250 Exothermic and endothermic reactions 9 questions

Chemistry Paper 3 June 2025 Foundation tier, Question 12 5 marks

A student investigates some exothermic and endothermic reactions.

They measure the temperature change in two reactions.

The table shows their results.

ReactionStart temperature (°C)End temperature (°C)Temperature change (°C)
1................12–4
21839+21
(a)

Complete the table by writing in the start temperature for Reaction 1.

[1]
Reveal mark scheme Mark scheme for question 12(a)
(b)

State and explain which reaction is exothermic and which is endothermic.

[2]
Reveal mark scheme Mark scheme for question 12(b)
(c)

The diagram shows a reaction profile for an exothermic reaction.

Figure for question 12
Question 12, shown as an image
(c)(i)

Which energy change, A, B or C, is the activation energy?

[1]
Reveal mark scheme Mark scheme for question 12(c)(i)
(c)(ii)

Which energy change, A, B or C, is the energy change for the reaction?

[1]
Reveal mark scheme Mark scheme for question 12(c)(ii)

Chemistry Paper 3 June 2023 Foundation tier, Question 14 14 marks

Zinc, Zn, reacts with sulfuric acid, H2SO4, to form the salt, ZnSO4, and hydrogen.

(a)

Write the balanced symbol equation for the reaction of zinc with sulfuric acid.

[1]
Reveal mark scheme Mark scheme for question 14(a)
(b)

Name the salt, ZnSO4, made from zinc and sulfuric acid.

[1]
Reveal mark scheme Mark scheme for question 14(b)
(c)

To make sure all the sulfuric acid reacts, an excess of zinc is used.

Describe how universal indicator could be used to show that all the sulfuric acid has reacted.

[2]
Reveal mark scheme Mark scheme for question 14(c)
(d)(i)

Calculate the relative formula mass of ZnSO4.

Relative atomic mass (Ar): O = 16.0 S = 32.1 Zn = 65.4

Relative formula mass of ZnSO4 =........

[1]
Reveal mark scheme Mark scheme for question 14(d)(i)
(d)(ii)

The percentage mass of an element in a compound can be calculated using the formula

Question 14, shown as an image

Calculate the percentage mass of zinc in ZnSO4.

Give your answer to 1 decimal place.

[3]
Reveal mark scheme Mark scheme for question 14(d)(ii)
(e)

The reaction between zinc and sulfuric acid is exothermic.

(e)(i)

Explain what is meant by an exothermic reaction.

[1]
Reveal mark scheme Mark scheme for question 14(e)(i)
(e)(ii)

The diagram shows the reaction profile for the reaction.

Figure for question 14

Label the activation energy on the diagram.

[1]
Reveal mark scheme Mark scheme for question 14(e)(ii)
(e)(iii)

Explain the term activation energy.

[1]
Reveal mark scheme Mark scheme for question 14(e)(iii)
(f)

The table shows the temperature changes in four reactions.

The reaction between zinc and sulfuric acid is slightly exothermic.

Which shows the reaction between zinc and dilute sulfuric acid?

Give a reason for your answer.

ReactionStart temperature (°C)End temperature (°C)
A2019
B2064
C2022
D2020
[3]
Reveal mark scheme Mark scheme for question 14(f)

Chemistry Paper 3 June 2022 Foundation tier, Question 3 1 mark

The table shows the start and end temperatures of four different reactions.

ReactionStart temperature (°C)End temperature (°C)
A–39
B1437
C2016
D2323

Which reaction is endothermic?

Question 3, shown as an image
[1]
Reveal mark scheme Mark scheme for question 3

Chemistry Paper 3 November 2021 Foundation tier, Question 17, also on the Higher paper 12 marks

The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction.

A student investigates the temperature change for the reaction.

The diagram shows the equipment the student uses.

Figure for question 17

50 cm3 of sodium hydrogen carbonate solution

The student adds 0.65 g of solid citric acid to an excess of sodium hydrogen carbonate solution.

The student measures the temperature change. The temperature change is 3.5 °C.

(a)(i)

How does a temperature change show that a reaction is endothermic?

[1]
Reveal mark scheme Mark scheme for question 17(a)(i)
(a)(ii)

How should the student have written the temperature change to show that this reaction is endothermic?

[1]
Reveal mark scheme Mark scheme for question 17(a)(ii)
(b)

Describe how the student performed the experiment so that they could calculate the temperature change.

[2]
Reveal mark scheme Mark scheme for question 17(b)
(c)

The student repeats the experiment using a different mass of citric acid. This time the student measures a larger temperature change.

The temperature change is 10.0 °C.

If 0.65 g of citric acid gives a temperature change of 3.5 °C, calculate the mass of citric acid, in milligrams, that gives a 10.0 °C temperature change.

1 g = 1000 mg

Give your answer to 3 significant figures.

[4]
Reveal mark scheme Mark scheme for question 17(c)
(d)

When the student washed out the plastic cup at the end of the second experiment they saw some excess solid left.

Explain how this affected the student’s result and describe how the student could have improved their experiment.

[3]
Reveal mark scheme Mark scheme for question 17(d)
(e)

Citric acid and sodium hydrogen carbonate react to form sodium citrate.

Sodium citrate contains sodium ions, Na+, and citrate ions, C6H5O73–.

Write the formula of sodium citrate.

[1]
Reveal mark scheme Mark scheme for question 17(e)

Chemistry Paper 4 November 2021 Foundation tier, Question 14 7 marks

A student investigates heating hydrated copper(II) sulfate, CuSO4.5H2O.

The diagram shows the experiment they do.

Figure for question 14

The student:

• Measures the mass of a boiling tube.

• Puts about 5 g of hydrated copper(II) sulfate in the boiling tube and measures the mass.

• Gently heats the boiling tube for one minute.

• Lets the boiling tube cool down and measures the mass.

During the experiment the hydrated copper(II) sulfate turns from blue to white and water vapour is produced.

Look at the student’s results.

Figure for question 14
(a)

Calculate the mass of water produced in the experiment.

[1]
Reveal mark scheme Mark scheme for question 14(a)
(b)

The student expected a greater mass of water to be produced.

How could they improve the experiment so a greater mass of water vapour is produced?

[1]
Reveal mark scheme Mark scheme for question 14(b)
(c)
Figure for question 14
(c)(i)

Complete and balance the symbol equation.

[2]
Reveal mark scheme Mark scheme for question 14(c)(i)
(c)(ii)

The student adds a few drops of water to a boiling tube containing some of the white solid.

Describe what the student observes happening to the white solid.

Give a reason for your answer.

Observation........

Reason........

[2]
Reveal mark scheme Mark scheme for question 14(c)(ii)
(c)(iii)

As water reacts with the white solid, the temperature of the boiling tube increases.

What name is given to this type of reaction where heat is transferred to the surroundings?

[1]
Reveal mark scheme Mark scheme for question 14(c)(iii)

Chemistry Paper 9 November 2021 Higher tier, Question 11, also on the Foundation paper 12 marks

The reaction between solid citric acid and sodium hydrogen carbonate solution is an endothermic reaction.

A student investigates the temperature change for the reaction.

The diagram shows the equipment the student uses.

Figure for question 11

50 cm3 of sodium hydrogen carbonate solution

The student adds 0.65 g of solid citric acid to an excess of sodium hydrogen carbonate solution.

The student measures the temperature change. The temperature change is 3.5 °C.

(a)(i)

How does a temperature change show that a reaction is endothermic?

[1]
Reveal mark scheme Mark scheme for question 11(a)(i)
(a)(ii)

How should the student have written the temperature change to show that this reaction is endothermic?

[1]
Reveal mark scheme Mark scheme for question 11(a)(ii)
(b)

Describe how the student performed the experiment so that they could calculate the temperature change.

[2]
Reveal mark scheme Mark scheme for question 11(b)
(c)

The student repeats the experiment using a different mass of citric acid. This time the student measures a larger temperature change.

The temperature change is 10.0 °C.

If 0.65 g of citric acid gives a temperature change of 3.5 °C, calculate the mass of citric acid, in milligrams, that gives a 10.0 °C temperature change.

1 g = 1000 mg

Give your answer to 3 significant figures.

[4]
Reveal mark scheme Mark scheme for question 11(c)
(d)

When the student washed out the plastic cup at the end of the second experiment they saw some excess solid left.

Explain how this affected the student’s result and describe how the student could have improved their experiment.

[3]
Reveal mark scheme Mark scheme for question 11(d)
(e)

Citric acid and sodium hydrogen carbonate react to form sodium citrate.

Sodium citrate contains sodium ions, Na+, and citrate ions, C6H5O73–.

Write the formula of sodium citrate.

[1]
Reveal mark scheme Mark scheme for question 11(e)

Chemistry Paper 3 June 2019 Foundation tier, Question 16, also on the Higher paper 12 marks

A student investigates three reactions.

She wants to find out if the reactions are exothermic or endothermic.

Look at her results.

ReactionStart temperature (°C)Final temperature (°C)
X2125
Y2018
Z2224
(a)

Which reaction, X, Y or Z, is endothermic ?........

Explain your answer.

[2]
Reveal mark scheme Mark scheme for question 16(a)
(b)

Draw a labelled reaction profile for an endothermic reaction.

Use the following labels on your reaction profile:

• products

• energy change

• activation energy.

Figure for question 16
[4]
Reveal mark scheme Mark scheme for question 16(b)
(c)

Another student repeats the same reactions.

The student does the experiment in a polystyrene cup instead of a beaker.

Explain why using a polystyrene cup is an improvement to the method.

[2]
Reveal mark scheme Mark scheme for question 16(c)
(d)

The reaction between iron oxide and aluminium is very exothermic.

Look at the equation for the reaction.

Question 16, shown as an image
(d)(i)

During this reaction the aluminium is oxidised.

Explain what is meant by the term oxidised.

[1]
Reveal mark scheme Mark scheme for question 16(d)(i)
(d)(ii)

Pure iron metal is produced in the reaction.

Draw a diagram to show the bonding in a metal.

Label your diagram clearly.

[3]
Reveal mark scheme Mark scheme for question 16(d)(ii)

Chemistry Paper 9 June 2019 Higher tier, Question 11, also on the Foundation paper 12 marks

A student investigates three reactions.

She wants to find out if the reactions are exothermic or endothermic.

Look at her results.

ReactionStart temperature (°C)Final temperature (°C)
X2125
Y2018
Z2224
(a)

Which reaction, X, Y or Z, is endothermic ?........

Explain your answer.

[2]
Reveal mark scheme Mark scheme for question 11(a)
(b)

Draw a labelled reaction profile for an endothermic reaction.

Use the following labels on your reaction profile:

• products

• energy change

• activation energy.

Figure for question 11
[4]
Reveal mark scheme Mark scheme for question 11(b)
(c)

Another student repeats the same reactions.

The student does the experiment in a polystyrene cup instead of a beaker.

Explain why using a polystyrene cup is an improvement to the method.

[2]
Reveal mark scheme Mark scheme for question 11(c)
(d)

The reaction between iron oxide and aluminium is very exothermic.

Look at the equation for the reaction.

Question 11, shown as an image
(d)(i)

During this reaction the aluminium is oxidised.

Explain what is meant by the term oxidised.

[1]
Reveal mark scheme Mark scheme for question 11(d)(i)
(d)(ii)

Pure iron metal is produced in the reaction.

Draw a diagram to show the bonding in a metal.

Label your diagram clearly.

[3]
Reveal mark scheme Mark scheme for question 11(d)(ii)

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