Exothermic & Endothermic Reactions (AQA GCSE Chemistry: Combined Science)

Exam Questions

2 hours18 questions
1a4 marks

A student investigated the amount of energy released when different types of food were burnt using the apparatus in Figure 1.

Figure 1

aqa-gcse-5-1e-tq1a-burning-food

The student used the following method and used the same mass of each food type:

  • Pour cold water into a boiling tube
  • Measure the starting temperature of the water
  • Heat the food until it catches fire
  • Heat the water using the flame from the burning food
  • Measure the final temperature of the water

Draw lines to show which are the correct identities of the independent and control variables in this experiment.

You may draw more than one line from each variable.

burning-food-variables

1b
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1 mark

The results of the investigation are shown in Table 1.

Table 1

Food type
  Crisp Biscuit Bread Cake
Starting temperature of the water in oC 21 21 22 21
Final temperature of the water in oC 32   26 28
Temperature change of the water in oC 11 9 4 7


What was the final temperature of the water when the biscuit was burned?

1c2 marks

Which type of food released the most energy?

Type of food: _________________________________

Give a reason for your answer.

_____________________________________________________________________

_____________________________________________________________________

1d1 mark

These foods released energy when they were burned.

What word can be used to describe the reaction when food burns?

Tick (✓) one box.

Displacement  
Exothermic  
Neutralisation  
Endothermic  

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2a1 mark

This question is about exothermic and endothermic reactions.

Which of the following statements about exothermic and endothermic reactions is correct?

Tick (✓) one box.

In an exothermic reaction, energy is transferred to the surroundings and the temperature of the surroundings decreases  
In an endothermic reaction, energy is transferred to the surroundings and the temperature of the surroundings decreases  
In an exothermic reaction, energy is transferred from the surroundings and the temperature of the surroundings increases  
In an endothermic reaction, energy is transferred from the surroundings and the temperature of the surroundings decreases  
2b1 mark

25 cm3 of hydrochloric acid was mixed with 25 cm3 of sodium hydroxide.

The reaction is exothermic.

Would you expect the reaction mixture to rise or fall in temperature?

2c1 mark

What has happened to the total amount of energy in the universe once the reaction has taken place?

Tick (✓) one box.

It increases  
It decreases  
It stays the same  
2d3 marks

Complete the sentences using the word either exothermic or endothermic.

Thermal decomposition reactions are examples of ____________________ reactions.

Combustion reactions are examples of ____________________  reactions.

The reaction of citric acid with sodium hydrogencarbonate is an ____________________  reaction.

2e1 mark

Exothermic and endothermic reactions can be used in everyday life.

Give two examples of how they can be used and state whether it uses an exothermic reaction or endothermic reaction.

Everyday example 1:

__________________________________________________________________

Exothermic or endothermic?

__________________________________________________________________

Everyday example 2:

__________________________________________________________________

Exothermic or endothermic?

__________________________________________________________________

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3a4 marks

Reaction profiles can be drawn to show the exothermic and endothermic reactions. Figure 1 shows a reaction profile.

Figure 1

reaction-profile-to-label

What do the labels A, B, C and D represent?

Draw one line from each label to what it represents.

reaction-profile-labels

3b1 mark

Does the reaction profile shown in Figure 1 represent an exothermic or an endothermic reaction?

Give a reason for your answer:

Exothermic / endothermic: ____________________________

Reason:

_______________________________________________________________________

_______________________________________________________________________

3c1 mark

What is meant by the term activation energy?

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4a2 marks

A student investigated how the temperature change when sodium hydroxide, NaOH, and hydrochloric acid, HCl, were reacted together.

They used the following method.

  • Place 25 cm3 of the NaOH solution into the polystyrene cup
  • Measure and record the temperature of the solution
  • Add 5 cm3 of the dilute HCl and stir
  • Measure and record the highest temperature reached by the mixture
  • Repeat the previous steps increasing the amount of acid added by 5 cm3 each time

What would be the most suitable apparatus to take the necessary measurements with?

Draw one line from the measurement taken to the correct piece of apparatus.

apparatus-for-measurements

4b1 mark

Why is a polystyrene cup used instead of a glass beaker?

4c2 marks

The student carried out the investigation into how the temperature change is affected by the amount of hydrochloric acid added using the method is part a).

Their results are shown in Table 1.

Table 1

Maximum temperature in oC
Total volume of hydrochloric acid added in cm3 First trial Second trial Third trial Mean
5 20.5 21.0 20.7 20.7
10 24.0 24.6 24.4 24.3
15 23.5 28.9 29.3 29.1
20 30.8 31.0 31.3 31.0
25 32.6 32.2 32.4  
30 32.0 32.8 32.6 32.5
35 31.6 31.8 31.7 31.7
40 30.8 31.0 30.6 30.8


What is the mean maximum temperature reached when 25 cm3 of hydrochloric acid is added?

4d1 mark

The student noticed they had an anomalous result.

Identify the result by stating the volume of hydrochloric acid added and the trial (first, second or third) where the anomalous result occurred in the table below.

Volume of hydrochloric acid added in cm3  
Trial  
4e3 marks

The student made the following conclusion:

'The reaction between hydrochloric acid and sodium hydroxide is an endothermic reaction.'

State whether the student is correct or incorrect.

The student is ____________________

Give a reason for your answer referring to the results and energy transfer.

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5a
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3 marks

Chlorine reacts with methane in the presence of sunlight to produce chloromethane.

Figure 1 shows the displayed formulae for the reaction.

Figure 1

chlorine-and-methane-reaction

Use the bond energies given in the table to calculate the overall energy change for this reaction.

Bond Bond energy in kJ/mol
C - H 412
C - Cl 328
Cl - Cl 242
H - Cl 431
5b3 marks

Complete the sentences using the words in the box to explain about the overall energy change of the reaction in part a).

endothermic greater taken in
given out            less                     exothermic

The reaction between chlorine and methane is an ____________________ reaction.

This is because the energy ____________________ forming new bonds is ____________________ than the energy needed to break existing bonds.

5c2 marks

The reaction profile in Figure 2 was drawn for a similar reaction between bromine and methane, which is an exothermic reaction.

Figure 2

vH~yEaU4_incorrect-endo-reaction-profile-

Identify two errors with the reaction profile.

Tick (✓) two boxes.

The arrow for the activation energy should start from the reactants  
The x-axis (progress of reaction) is labelled incorrectly  
The arrow of the overall energy change should be in the opposite direction  
The energy of the reactants should be lower than the energy of the products  
The y-axis (energy) is labelled incorrectly  

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1a4 marks

The reaction between methane and oxygen occurs as shown:

CH4       +        2O2       →           CO2         +        2H2O

      methane          oxygen             carbon dioxide           water

The structural formulae shown in Figure 1 more clearly represents the bonds in each molecule involved in the reaction:

Figure 1

5-1-exothermic--endothermic-reactions-medium-q1a

In the three stages shown at (a), (b) and (c) below, calculate the net energy transfer when 1 mole of methane reacts with oxygen.

Complete Table 1 by identifying the type and number of bonds broken and bonds formed during the reaction.

Table 1

Bonds broken Bonds formed
Number Type Number Type
       
       
1b4 marks

Calculate the total energy changes involved in the process of breaking and forming these bonds using the bond energies in Table 2 .

Table 2

  C - H O = O C = O H - O
Energy in kJ per mole 412 498 805 464
1c2 marks

Describe in as much detail as you can what the results from part (b) tell you about the overall reaction.

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2
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1 mark

Which is true about chemical energy changes?

   Reaction type Energy flows Temperature of surroundings
A exothermic to the surroundings increases
B exothermic from the surroundings decreases
C endothermic to the surroundings decreases
D endothermic from the surroundings increases

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    3
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    1 mark

    The reaction profile for making nitrogen monoxide, NO, is shown below:

     u~9ImaV8_2

    What is the activation energy for this reaction?

    • +140 kJ

    • +180 kJ

    • +320 kJ

    • -330 kJ

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    4a2 marks

    Thunderstorms often produce lightning which can reach temperatures of up to 30,000 oC. 

    At these high temperatures oxygen and nitrogen in the air can react together and produce nitrogen oxide. 

    This is an endothermic reaction which has a very high activation energy.

    The equation for the reaction is:     N2 + O2 → 2NO

    The reaction profile for the reaction is shown in Figure 1.

    Figure 1

    6_Iondin_aqa-gcse-5-1m-tq4a-nitrogen-and-oxygen-reaction-profile

    Explain how the reaction profile shows that this reaction is endothermic.

    4b2 marks

    Explain what the term activation energy means and comment on its significance in terms of particle theory.

    4c4 marks

    The bond energies involved in the reaction are shown in the Table 1 below.

    Table 1
     
    Bond Bond energy in kJ
    N ≡ N 945
    O = O 498
    N = O 630
     

    Calculate the total energy change for the reaction showing clearly your working out including a balanced displayed formula equation of the reaction.

    4d3 marks

    Use the bond energies to explain why this reaction is endothermic.

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    5
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    1 mark

    How much energy is needed to break all the bonds in 0.025 g of nitrogen gas?

    Relative atomic mass (Ar): N = 14

    Bond  Bond energy in kJ/mol
    Nidentical toN  945

    • 1701 J

    • 1701 kJ

    • 844 J

    • 844 kJ

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    61 mark

    Endothermic reactions can be used in emergency sports injury treatment packs.

    What is true about these packs?

    • Absorb energy from the surroundings and transfer it to the injury

    • Can be re-used

    • Usually contain ammonium nitrate and water in separate compartments

    • Cause the temperature of the surroundings to increase

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    7a3 marks

    A student investigated displacement reactions by measuring the temperature change when metals are reacted with a copper sulfate solution.

    Table 1 shows the student’s results.

    Table 1

    Metal Temperature increase in oC
    Copper 0
    Iron 15
    Zinc 19
    Magnesium 42


    Plot the data from the table above on
    Figure 1 as a bar chart. 

    Figure 1

    5-1-exothermic--endothermic-reactions-medium-q2a

    7b2 marks

    The student evaluated the data and came to the conclusion that the reactions between the metals and copper sulfate solution are endothermic.

    Give two reasons why this conclusion is not correct.

    7c6 marks

    The magnitude of the temperature change observed depends on the reactivity of the metal.

    Describe a method that could determine the relative reactivity of an unknown metal compared to the four known metals, indicating how you would ensure the results are valid.

    7d5 marks

    Draw and label a reaction profile for the reaction between zinc and copper sulfate solution.

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    8a
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    4 marks

    Bromine reacts with methane in the presence of sunlight to produce bromomethane and hydrogen bromide.  

    Figure 1 shows the displayed formulae for the reaction between methane and bromine.

    Figure 1

    methane--bromine

     Table 1 below shows the bond energies and the overall energy change for the reaction.

    Table 1

    Bond C - H Br - Br C - Br H - Br Overall energy change
    Energy change in kJ/mol 412 193 X 366 -51

    Calculate the bond energy
    X for the C - Br bond, showing clearly your working out.
     

    8b3 marks

    State whether this reaction is endothermic or exothermic and explain why in terms of energy transfer.

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    1a2 marks

    A student investigated the temperature change in the reaction between dilute hydrochloric acid and potassium hydroxide solution.

    The equation for the reaction is:

    HCl + KOH → KCl + H2O

    The method the student used is shown below:

    Step 1 Put 25 cm3 of dilute hydrochloric acid into a polystyrene cup
    Step 2 Measure and record the temperature of the dilute hydrochloric acid
    Step 3 Add 5 cm3 of potassium hydroxide solution to the acid and stir
    Step 4 Measure and record the highest temperature reached by the mixture
    Step 5 Repeat steps 3 and 4 until 40 cm3 of potassium hydroxide solution has been added

    The student plotted their results and are shown in Figure 1.

    Figure 1

    aqa-gcse-5-1h-tq1a-temp-vs-vol-koh

    Draw two straight lines of best fit on Figure 1.

    1b3 marks

    Explain why the graph has this shape.

    Use data from the graph.

    1c2 marks

    Suggest one change that could be made that would give more accurate results.

    Explain your answer.

    1d2 marks

    Use the results in Figure 1 to state whether the reaction between dilute hydrochloric acid and potassium hydroxide solution is exothermic or endothermic.

    Give a reason for your answer.

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    2a
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    3 marks

    Methanol is an alcohol that will undergo a combustion reaction.

    The chemical equation for is:

    2CH3OH + 3O2 → 2CO2 + 4H2O

    The equation for the reaction can be also be shown as:

    combustion-of-methanol

    Table 1 shows the bond energies of different bonds.

    Table 1

    Bond Bond energy in kJ per mole
    C-C 347
    C=C 614
    C-H 413
    C-O 358
    C=O 799
    O-O 142
    O=O 495
    O-H 467


    Use the bond energies in Table 1 to calculate the overall energy change for the combustion of methanol.

    2b1 mark

    Explain why, in terms of bonds breaking and forming, the combustion of methanol is an exothermic reaction.

    2c3 marks

    Complete the reaction profile for the combustion of methanol shown in Figure 1.

    You need to label:

    • The products
    • The overall energy change
    • The activation energy

    Figure 1

    aqa-gcse-5-1h-tq2c-reaction-profile-combustion-methanol

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    3a6 marks

    Citric acid reacts with sodium hydrogencarbonate solution.

    A student investigated how the temperature changed during this reaction.

    The results they obtained are shown in Figure 1.

    Figure 1

    aqa-gcse-5-1h-tq3a-citric-acid--nahco3

    Describe a method for how these results could have been obtained.

    3b2 marks

    An anomalous result was obtained when 1.2 g of citric acid had been added to the sodium hydrogencarbonate solution.

    Suggest two reasons for the anomalous result.

    3c2 marks

    Using data from Figure 1, explain how the graph shows that this is an endothermic reaction and approximately how much citric acid is needed for the reaction to reach completion.

    3d2 marks

    Explain why the temperature increases when between 3.0 g and 4.0 g of citric acid is added to the sodium hydrogencarbonate solution.

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    4a3 marks

    Endothermic reactions can be used in everyday life. One use is in sports injury packs.

    A student looked at the reaction profiles of three different reactions to decide which reaction would be the most suitable to be used in a sports injury pack.

    The reaction profiles being investigated are shown in Figure 1.

    Figure 1

    aqa-gcse-5-1h-q4a-sports-injury-pack-reaction-profile

    Suggest which of the reactions would be the most suitable for using in a sports injury pack.

    Give reasons for your answer. 

    4b2 marks

    The student thought that the reaction would need to have a low activation energy in order to be effective.

    Define activation energy and explain how activation energy can be shown on a reaction profile.

    4c2 marks

    Explain why a reaction with a lower activation energy would be more suitable in a sports injury pack than a reaction with a high activation energy.

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    5a4 marks

    Sodium chloride dissolving in water is endothermic so the temperature of the water will decrease.

    A student investigated the temperature decrease of water when different masses of sodium chloride were added to 100 cm3 of water.

    Their results are shown in Table 1.

    Table 1

    Mass of sodium chloride added in g Final temperature of solution in oC
    15 13.0
    20 10.5
    25 8.0
    30 6.0
    35 3.0
    40 1.0
    45 1.0
    50 1.0


    Plot the results of Figure 1 and draw two straight lines of best fit through the points.

    Figure 1
    aqa-gcse-5-1h-q5a-graph-temperature-vs-mass-nacl
    5b2 marks

    Estimate the temperature of the room that the investigation was carried out at.

    Use the graph drawn on Figure 1 and show your working on the graph.

    5c2 marks

    It is difficult to use the data in Table 1 to find the exact mass of sodium chloride that would give the minimum final temperature.

    Suggest further experimental work that the student should do to make it easier to find the exact mass of sodium chloride that would give the minimum final temperature.

    5d2 marks

    The student repeated the investigation but used 200 cm3 of water instead of 100 cm3.

    What would you expect to happen to the minimum final temperature?

    Explain your answer.

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