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GCSEChemistry: Combined ScienceEdexcelExam Questions6. Rates of Reaction & Energy Changes6.2 Heat Energy Changes in Chemical Reactions

Heat Energy Changes in Chemical Reactions (Edexcel GCSE Chemistry: Combined Science)

Exam Questions

2 hours17 questions
Easy
Medium
1a3 marks

A student investigated the reaction between potassium iodide and lead nitrate.

i)
Solutions of potassium iodide and lead nitrate were mixed together.

Lead iodide and potassium nitrate were formed.

Complete the word equation.
....................... + ....................... → ....................... + .......................
.......................   .......................   .......................   .......................
(2)
   
  
ii)
The student recorded the total mass of the reactants and the total mass of the products.

The results are shown in Figure 4.

  Reactants Products
total mass in g 21.7 21.7

Figure 4

State how the results in Figure 4 show that mass is conserved in this reaction.

(1)

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1b5 marks

In another experiment, a student investigated the temperature decrease when different amounts of ammonium nitrate crystals were dissolved in 100 cm3 of water.

The apparatus used is shown in Figure 5.

fig-5-q3b-1cho-2f-paper-1-nov-2020

Figure 5

The student used the following method.

 
step 1

pour 100 cm3 of water into the polystyrene cup
step 2 add one spatula of ammonium nitrate crystals to the water
step 3 stir the mixture
step 4 use the thermometer to record the lowest temperature reached by the mixture
step 5 repeat steps 1 to 4 using different amounts of ammonium nitrate
 
i)
Name a piece of apparatus that should be used to measure the 100 cm3 of water in step 1.
 
(1)
 
ii)
The student cannot work out the temperature decrease using the method described.
State what the student must do before step 2 to be able to work out the temperature decrease.
 
(1)
 
iii)
State why a polystyrene cup is used in this experiment.
 
(1)
 
iv)
Figure 6 shows the reaction profile for this reaction.
 
Use the words from the box to complete the labels on Figure 6.
 
activation energy               products             reactants

(2)

fig-6-q3biv-1cho-2f-paper-1-nov-2020

Figure 6

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2a3 marks

Chemical reactions involve a change in energy as the bonds are broken and new bonds are formed. They can be classified as endothermic or exothermic depending on the energy changes that occur.

The table contains statements about endothermic and exothermic reactions.

Put a tick (✔) in the box to show whether a statement relates to an endothermic reaction or an exothermic reaction.

 
 
  Endothermic Exothermic
 The reaction releases energy to the surroundings    
 The process of bond breaking is...    
 Neutralisation is an example of this type of reaction    

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2b3 marks

The reaction profile diagram in Figure 1 shows that the thermal decomposition of calcium carbonate is an endothermic reaction. 

 
CaCO3 (s) → CaO (s) + CO2 (g)
 
7-2-2b-e-a
 
 

The reaction between magnesium and sulfuric acid is an exothermic reaction.

   
Mg (s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)
 

Complete the reaction profile diagram in Figure 2 for the reaction of magnesium and sulfuric acid.

 
7-2-2b-e-b
 

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2c2 marks

Key pieces of information can be gathered from a reaction profile diagram as shown in Figure 3.

 
7-2-2c-e-caco3-thermal-decomp-reaction-profile-labels
 
 

Name the two pieces of key information that are labelled on Figure 3.

  
1 = ____________________
 
2 = ____________________ 

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2d2 marks

In terms of activation energy, explain how a catalyst speeds up the rate of a chemical reaction.

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3a4 marks

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

aqa-gcse-5-1e-tq3a-reaction-profile-to-label

Figure 1

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

Draw one line from each label to what it represents.

screenshot-2024-01-19-130842

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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:

_______________________________________________________

_______________________________________________________

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3c1 mark

What is meant by the term activation energy?

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4a1 mark

This question is about exothermic and endothermic reactions.

Which statement about exothermic and endothermic reactions is true?

  ☐ A Exothermic reactions involve the breaking of bonds 
  ☐ B In an endothermic reaction, energy is taken in from the surroundings
  ☐ C Bond formation is an endothermic process
  ☐ D In an exothermic reaction the temperature of the surroundings will decrease

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4b1 mark

A students investigates whether the reaction between hydrochloric acid was mixed with of sodium hydroxide is exothermic or endothermic. 

Name the piece of apparatus used to measure the temperature change. 

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4c1 mark

What type of reaction occurs between sodium hydroxide and hydrochloric acid? 

  ☐ A Neutralisation
  ☐ B Displacement 
  ☐ C Oxidation
  ☐ D Combustion

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4d3 marks

Many different reactions are exothermic or endothermic. 

Complete the sentences to identify the reaction as either exothermic or endothermic. 

Thermal decomposition reactions are examples of ____________________ reactions.

Combustion reactions are examples of ____________________  reactions.

Precipitation reactions are examples of  ____________________  reactions.

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5a4 marks

A student investigates some exothermic and endothermic reactions.

He measures the temperature changes during some chemical reactions.

His results are shown in Figure 1. 

Reaction Temperature at start (°C) Temperature at end (°C) Temperature change (°C)
1 15 25 +10
2 15 15 0
3 18 15 -3
4 15 20 +5

Figure 1

What can you conclude about the type of energy change in each reaction?

Explain your answer.

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5b1 mark
A student does an experiment with an acid and an alkali.

q16b-paper-1-specimen-2016-ocr-gcse-chemistry
1
He adds the acid to a beaker and measures its temperature.
2.
He then adds the alkali to the beaker and stirs the mixture.
3.

At the end of the reaction, he removes the thermometer from the beaker and measures the temperature.

Explain why the student should have used a polystyrene cup instead of a beaker.

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5c
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A student adds water to calcium oxide. A vigorous exothermic reaction takes place forming calcium hydroxide.

Calcium hydroxide has the formula Ca(OH)2.

Show that the relative formula mass (Mr) of calcium hydroxide is 74.1.

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1a1 mark

When solid ammonium chloride is shaken with water, a colourless solution forms and the temperature changes from 20°C to 16°C.

Give the name of the type of heat change occurring.

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1b
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A student carries out an experiment to measure accurately the temperature changes when different metals are added to iron(II) sulfate solution.

The method for the experiment is:

  • measure 25cm3 of iron(II) sulfate solution and pour into a container
  • record the initial temperature of the solution
  • add excess magnesium ribbon
  • record the highest temperature of the mixture
  • repeat the experiment using excess copper turnings, then using excess zinc foil.
i)
State a suitable container for the iron(II) sulfate solution in this experiment.

(1)

ii)
State what the student should do to the mixtures during the experiment.

(1)

iii)
Figure 5 shows the results obtained by the student.

metal added to
iron(II) sulfate solution		 temperature rise
/ °C
magnesium 6.0
copper 0.0
zinc 2.8

Figure 5

Explain the order of reactivity of the metals magnesium, copper and zinc using the results.

(2)

iv)
Explain how the student could improve the method to make a fairer comparison of the temperature change produced by the different metals.

(2)

v)
The iron(II) sulfate solution contained 6.2 g of iron(II) sulfate in 50 cm3 of solution.

Calculate the concentration of the iron(II) sulfate solution in g dm–3.

(2)

concentration = .............................................................. g dm–3

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21 mark

Which statement describes activation energy?

  ☐ A The energy level of the reactants
  ☐ B The energy level of the products
  ☐ C The energy needed to break the bonds in the reactants
  ☐ D The difference in energy level between the reactants and products

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3a1 mark

Higher Only

Each of these substances forms ions in solution.

One mole of the following substances is dissolved in 1 dm3 of water.

Which solution contains the greatest number of ions?

  ☐ A ammonium sulfate, (NH4)2SO4
  ☐ B iron(III) chloride, FeCl3
  ☐ C magnesium nitrate, Mg(NO3)2
  ☐ D potassium bromide, KBr

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3b4 marks

When sodium hydroxide solution is neutralised with an acid there is a temperature change.

A student is given dilute hydrochloric acid and dilute ethanoic acid of the same concentration in mol dm−3.

Devise a plan to compare the temperature changes produced when sodium hydroxide solution is neutralised with each of these two acids.

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3c3 marks

Hydrogen reacts with chlorine to form hydrogen chloride.

H2 (g) + Cl2 (g) → 2HCl (g)

The reaction is exothermic.

Draw and label the reaction profile diagram for this reaction, identifying the activation energy.

fig-q10c-1cho-2h-specimen-2018

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3d4 marks

Higher Only

The energies of some bonds are shown in Figure 13.

bond energy of bond /kJmol–1
H–H 436
Cl–Cl 243
H–Cl 432

Figure 13

Hydrogen reacts with chlorine to form hydrogen chloride.

H2 (g) + Cl2 (g) → 2HCl (g)

Calculate the energy change, in kJ mol–1, for the reaction of 1 mol of hydrogen gas, H2 with 1 mol of chlorine gas, Cl2, to form 2 mol of hydrogen chloride gas, HCl.

(4)

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4
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Higher Tier Only

Chlorine reacts with methane in sunlight.

 CH4 + Cl2  → CH3Cl + HCl

The diagram below shows the displayed formulae for the reaction of chlorine with methane.

3-1-q9-edexcel-igcse-chemistry 

The table below shows the bond energies and the overall energy change in the reaction. 

  C-H Cl-Cl C-Cl H-Cl Overall energy change
Energy in kJ/mol 413 243 X 432 -122

What is the value of X?

  ☐ A 67 kJ
  ☐ B 134 kJ
  ☐ C 346 kJ
  ☐ D 542 kJ

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5
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Higher Tier Only

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

The relative atomic mass, Ar, of N is 14.

Bond  Bond energy in kJ/mol
Nidentical toN  945

  ☐ A 1701 J
  ☐ B 1701 kJ
  ☐ C 844 J
  ☐ D 844 kJ

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6a2 marks

Students are investigating exothermic and endothermic reactions.
They are finding the temperature change in 50 cm3 water when a solid dissolves in it.
The apparatus is shown in Figure 1.

fig-1-q1-1cho-2f-paper-1-june-2018

Figure 1

The steps needed to carry out this experiment are P, Q, R, S and T.
They are shown below.

They are not in the correct order.
P pour the 50 cm3 water into the polystyrene cup
Q add the solid to the water and stir
R measure 50 cm3 water using a beaker
S measure the initial temperature of the water
T measure the final temperature of the solution when all the solid has dissolved

Write the steps in the correct order, from left to right.
fig-q1-1cho-2f-paper-1-june-2018

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6b1 mark

The dissolving of this solid in water is an exothermic change.
The experiment is repeated a number of times.
Compared with the initial temperature of the water, the final temperature of the solution is

  ☐ A always higher
  ☐ B always lower
  ☐ C sometimes higher and sometimes lower
  ☐ D always unchanged

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6c1 mark

State how step R could be changed to measure the volume of water more accurately.

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6d3 marks

Figure 2 shows a cold pack.

PKtcBthE_fig-2-q1d-1cho-2f-paper-1-june-2018

When the pack is squeezed hard the inner bag bursts.
Then the pack goes cold.

i)
Explain why the pack goes cold.

(2)

ii)
Give the reason why the pack can be used only once.

(1)

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71 mark

The graph below shows a reaction profile for the reaction between methane and oxygen. 

 3-1-q7-edexcel-igcse-chemistry

What does the label X represent?

  ☐ A Activation Energy
  ☐ B Overall energy change
  ☐ C Reactants
  ☐ D Progress of the reaction

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81 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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9a1 mark

A student poured 50 cm3 water into a beaker and measured the water’s temperature.

fig-7-q4-1cho-2f-paper-1-june-2019

Figure 7

The student added 1.00g calcium chloride to the water, stirred the mixture and then recorded the temperature.

Give the name of the apparatus that could be used to measure 1.00 g of calcium chloride.

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9b
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The student’s results were

 
      temperature of water at start       = 21°C
      temperature of mixture after stirring  = 32°C
 

Explain, using these results, the type of heat energy change that occurs when calcium chloride dissolves in water.

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9c2 marks

Calcium chloride is hazardous to health.

 
i)
Which hazard symbol would be expected to be seen on a container of calcium chloride?
 
(1)
  ☐ A fig-q4cia-1cho-2f-paper-1-june-2019
  ☐ B fig-q4cib-1cho-2f-paper-1-june-2019
  ☐ C fig-q4cic-1cho-2f-paper-1-june-2019
  ☐ D fig-q4cid-1cho-2f-paper-1-june-2019

ii)
Give a safety precaution that the student should take during the experiment.
 
(1)

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9d1 mark

State one way in which the apparatus could be changed to reduce the amount of heat energy lost during the experiment.

 

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9e3 marks

The concentration of a calcium chloride solution is 12 g dm–3.

Calculate the volume of this solution, in cm3, that contains 9.0 g of calcium chloride.

You must show your working.

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10
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The reaction profile for making nitrogen monoxide, NO, is shown below:

 3-1-q8-edexcel-igcse-chemistry

What is the activation energy for this reaction?

  ☐ A +140 kJ
  ☐ B +180 kJ
  ☐ C +320 kJ
  ☐ D -330 kJ

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11a
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The concentration of a solution can be calculated using the equation

concentration space of space solution space equals space fraction numerator mass space of space solid over denominator volume space of space solution end fraction

A student dissolved 9.25 g of ammonium chloride in water and made up the solution to a volume of 200 cm3


Use the equation to calculate the concentration of this solution in g dm−3.

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11b5 marks

Dissolving ammonium chloride in water is an endothermic process.
Figure 17 shows part of the reaction profile for this process.

fig-17-q8b-1cho-2f-paper-1-nov-2021

Figure 17

i)
Explain how Figure 17 shows that dissolving ammonium chloride in water is an endothermic process.
(3)
ii)
Complete the reaction profile in Figure 17 and label the activation energy.

(2)

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11c3 marks

A student used the equipment in Figure 18 to investigate whether electricity can pass through solid ammonium chloride and through ammonium chloride solution.

fig-18-q8c-1cho-2f-paper-1-nov-2021

Figure 18

If an electrical current flows in the circuit, the lamp will light up.


Figure 19 shows the results of the investigation.

substance lamp
solid ammonium chloride did not light up
ammonium chloride solution lit up brightly

Figure 19

Explain the results of the investigation.

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11d2 marks

Ammonia gas is toxic.

i)
Which symbol should be placed on a container of a toxic gas?

(1)

q9a-1cho-2f-paper-1-nov-2021

ii)
Give one safety precaution that should be taken when working with toxic gases in the laboratory.

(1)

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121 mark

Which statement is true about exothermic and endothermic reactions?

  ☐ A The products have more energy than the reactants in an exothermic reaction
  ☐ B The products have more energy than the reactants in an endothermic reaction
  ☐ C The activation energy for an exothermic reaction is always larger than the activation energy for an endothermic reaction
  ☐ D Most reactions are endothermic

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