Exothermic and endothermic reactions
5.1What the syllabus asks of you
- State that an exothermic reaction transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings
- State that an endothermic reaction takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings
- State that the transfer of thermal energy during a reaction is called the enthalpy change, ΔH, of the reaction. ΔH is negative for exothermic reactions and positive for endothermic reactions
- Define activation energy, Ea, as the minimum energy that colliding particles must have to react
- Draw, label and interpret reaction pathway diagrams for exothermic and endothermic reactions using information provided, to include: (a) reactants (b) products (c) enthalpy change of the reaction, ΔH (d) activation energy, Ea
- State that bond breaking is an endothermic process and bond making is an exothermic process and explain the enthalpy change of a reaction in terms of bond breaking and bond making
- Calculate the enthalpy change of a reaction using bond energies
Read the notes first
Chapter 5: Exothermic and endothermic reactions
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Every question on Exothermic and endothermic reactions, untimed, marked as you go.
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46 questions
1May / June 2026 · Paper 11 · Q14Show mark scheme →
A–1583 kJ/mol
B–1318 kJ/mol
C–655 kJ/mol
D–390 kJ/mol
Mark scheme
2May / June 2026 · Paper 12 · Q12Show mark scheme →
Aoverall energy change: energy released when bonds are made is greater than energy used to break bonds; ΔH: negative
Boverall energy change: energy released when bonds are made is less than energy used to break bonds; ΔH: negative
Coverall energy change: energy released when bonds are made is greater than energy used to break bonds; ΔH: positive
Doverall energy change: energy released when bonds are made is less than energy used to break bonds; ΔH: positive
Mark scheme
3May / June 2026 · Paper 12 · Q14Show mark scheme →
AA
BB
CC
DD
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4Oct / Nov 2025 · Paper 11 · Q14Show mark scheme →
A–728 kJ / mol
B–568 kJ / mol
C–34 kJ / mol
D+352 kJ / mol
Mark scheme
5Oct / Nov 2025 · Paper 12 · Q12Show mark scheme →
AA reaction in which the number of bonds broken equals the number of bonds formed always has an enthalpy change, ΔH = 0.
BCombustion can be either exothermic or endothermic.
CIn exothermic reactions, thermal energy is transferred to the surroundings, so the temperature of the surroundings increases.
DThe activation energy, Ea, for a reaction is the minimum energy particles must have in order to collide.
Mark scheme
6Oct / Nov 2025 · Paper 12 · Q13Show mark scheme →
A+240 kJ / mol
B+3 kJ / mol
C–3 kJ / mol
D–246 kJ / mol
Mark scheme
7May / June 2025 · Paper 11 · Q16Show mark scheme →
Aenergy of bonds broken greater than energy of bonds formed; endothermic
Benergy of bonds broken less than energy of bonds formed; exothermic
Cenergy of bonds broken greater than energy of bonds formed; exothermic
Denergy of bonds broken less than energy of bonds formed; endothermic
Mark scheme
8May / June 2025 · Paper 12 · Q15Show mark scheme →
A2H(g) + O(g) → H₂O(g)
BH₂(g) → 2H(g)
CH₂O(g) → H₂O(l)
D2O(g) → O₂(g)
Mark scheme
9Oct / Nov 2024 · Paper 11 · Q13Also set in Oct / Nov 2019 Paper 11Show mark scheme →
AIn an endothermic reaction, energy is used to break bonds but no energy is released when bonds form.
BIn an endothermic reaction, energy is released when bonds form but more energy is used to break bonds.
CIn an exothermic reaction, energy is released both by breaking and by forming bonds.
DIn an exothermic reaction, energy is released when bonds form but no energy is needed to break bonds.
Mark scheme
10Oct / Nov 2024 · Paper 12 · Q15Show mark scheme →
Aendothermic — More energy is required to break the bonds than the energy released when the bonds are formed.
Bendothermic — Less energy is required to break the bonds than the energy released when the bonds are formed.
Cexothermic — More energy is required to break the bonds than the energy released when the bonds are formed.
Dexothermic — Less energy is required to break the bonds than the energy released when the bonds are formed.
Mark scheme
11May / June 2024 · Paper 11 · Q14Show mark scheme →
A1, 2 and 3
B1 and 2 only
C1 and 3 only
D2 and 3 only
Mark scheme
12May / June 2024 · Paper 11 · Q15Show mark scheme →
A–920 kJ / mol
B–834 kJ / mol
C–484 kJ / mol
D+442 kJ / mol
Mark scheme
13May / June 2024 · Paper 12 · Q14Also set in Oct / Nov 2018 Paper 11, Oct / Nov 2018 Paper 12Show mark scheme →
A1 and 3
B1 and 4
C2 and 3
D2 and 4
Mark scheme
14May / June 2024 · Paper 12 · Q15Show mark scheme →
A–247 kJ / mol
B–184 kJ / mol
C+184 kJ / mol
D+247 kJ / mol
Mark scheme
15Oct / Nov 2023 · Paper 11 · Q14Show mark scheme →
A–447 kJ/mol
B–283 kJ/mol
C+141.5 kJ/mol
D+283 kJ/mol
Mark scheme
16Oct / Nov 2023 · Paper 11 · Q15Show mark scheme →
A–263 kJ / mol
B–103 kJ / mol
C+103 kJ / mol
D+263 kJ / mol
Mark scheme
17Oct / Nov 2023 · Paper 12 · Q13Show mark scheme →
A–247 kJ/mol
B–184 kJ/mol
C+184 kJ/mol
D+247 kJ/mol
Mark scheme
18Oct / Nov 2023 · Paper 12 · Q14Show mark scheme →
A+16.5 kJ
B+33 kJ
C+66 kJ
D+132 kJ
Mark scheme
19May / June 2023 · Paper 11 · Q12Show mark scheme →
A1 and 2 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
Mark scheme
20May / June 2023 · Paper 12 · Q14Show mark scheme →
A–620 kJ / mol
B–238 kJ / mol
C+238 kJ / mol
D+620 kJ / mol
Mark scheme
21Oct / Nov 2022 · Paper 12 · Q19Show mark scheme →
Aenergy profile diagram A
Benergy profile diagram B
Cenergy profile diagram C
Denergy profile diagram D
Mark scheme
22Oct / Nov 2022 · Paper 12 · Q20Also set in Oct / Nov 2022 Paper 11Show mark scheme →
Acombustion and cracking
Bcombustion and fermentation
Ccracking and photosynthesis
Drespiration and photosynthesis
Mark scheme
23May / June 2022 · Paper 11 · Q18Show mark scheme →
A–110 kJ / mol
B–10 kJ / mol
C+10 kJ / mol
D+110 kJ / mol
Mark scheme
24May / June 2022 · Paper 11 · Q19Show mark scheme →
Athe reaction is endothermic; the value of ΔH is negative
Bthe reaction is endothermic; the value of ΔH is positive
Cthe reaction is exothermic; the value of ΔH is negative
Dthe reaction is exothermic; the value of ΔH is positive
Mark scheme
25May / June 2022 · Paper 12 · Q18Show mark scheme →
Acombustion of methane
Bcracking of hydrocarbons
Cdecomposition of water into hydrogen and oxygen by electrolysis
Dphotosynthesis in plants
Mark scheme
26Oct / Nov 2021 · Paper 11 · Q16Show mark scheme →
Aatoms bonding to form molecules
Bthe chemical reaction occurring in a fuel cell
Cthe reaction of carbon dioxide and water to produce glucose and oxygen
Dthe reaction of methane with oxygen to produce water and carbon dioxide
Mark scheme
27Oct / Nov 2021 · Paper 11 · Q17Show mark scheme →
AThe total energy of bond formation is greater than the total energy of bond breaking.
BThe total energy of bond breaking is greater than the total energy of bond formation.
CThe temperature of the reaction mixture falls during the reaction.
DThe temperature of the reaction mixture remains unchanged during the reaction.
Mark scheme
28Oct / Nov 2021 · Paper 12 · Q17Show mark scheme →
AThe reaction is exothermic.
BX represents the activation energy for the reaction.
CY represents ΔH for the reaction.
DZ represents the energy given out as the reaction proceeds.
Mark scheme
29Oct / Nov 2020 · Paper 11 · Q20Show mark scheme →
AA
BB
CC
DD
Mark scheme
30Oct / Nov 2020 · Paper 12 · Q20Show mark scheme →
A–200 kJ / mol
B–100 kJ / mol
C+100 kJ / mol
D+200 kJ / mol
Mark scheme
31Oct / Nov 2019 · Paper 11 · Q13Show mark scheme →
Aan endothermic energy change
Bthe activation energy
Cthe energy taken in by the reactants
Dthe enthalpy change of the reaction
Mark scheme
32Oct / Nov 2019 · Paper 12 · Q13Show mark scheme →
ABoth reactions are exothermic.
BOnly one reaction is endothermic.
CThe activation energy of reaction 1 is smaller than the activation energy of reaction 2.
DThe enthalpy change of reaction 2 is larger than the enthalpy change of reaction 1.
Mark scheme
33Oct / Nov 2019 · Paper 12 · Q14Show mark scheme →
A1 and 2 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
Mark scheme
34May / June 2019 · Paper 11 · Q16Show mark scheme →
AIt is endothermic and the activation energy is P – Q.
BIt is endothermic and the activation energy is P – R.
CIt is exothermic and the activation energy is P – Q.
DIt is exothermic and the activation energy is P – R.
Mark scheme
35May / June 2019 · Paper 12 · Q16Show mark scheme →
Athe reaction that is endothermic: backward reaction; the reaction with greater activation energy: backward reaction
Bthe reaction that is endothermic: backward reaction; the reaction with greater activation energy: forward reaction
Cthe reaction that is endothermic: forward reaction; the reaction with greater activation energy: backward reaction
Dthe reaction that is endothermic: forward reaction; the reaction with greater activation energy: forward reaction
Mark scheme
36Oct / Nov 2018 · Paper 11 · Q15Show mark scheme →
AThe activation energy for the reaction is equal to E.
BThe enthalpy change for the reaction is equal to E.
CThe reaction is exothermic.
DThe total energy needed to break bonds is greater than the total energy needed to form bonds.
Mark scheme
37Oct / Nov 2018 · Paper 12 · Q15Show mark scheme →
Aenergy profile diagram A
Benergy profile diagram B
Cenergy profile diagram C
Denergy profile diagram D
Mark scheme
38May / June 2018 · Paper 11 · Q16Show mark scheme →
A1, 2 and 3
B1 and 2 only
C2, 3 and 4
D3 and 4 only
Mark scheme
39May / June 2018 · Paper 12 · Q16Show mark scheme →
Aenergy profile diagram A with positive ΔH
Benergy profile diagram B with negative ΔH
Cenergy profile diagram C with positive ΔH
Denergy profile diagram D with negative ΔH
Mark scheme
40Oct / Nov 2017 · Paper 11 · Q17Show mark scheme →
A– 447 kJ / mol
B–283 kJ / mol
C+141.5 kJ / mol
D+283 kJ / mol
Mark scheme
41Oct / Nov 2017 · Paper 12 · Q18Show mark scheme →
ACompound Y can be used as a fuel.
BCompound Y could be a hydrocarbon.
CIn the reaction the energy needed to break bonds is greater than the energy released when bonds are made.
DIn the reaction the products are at a lower energy level than the reactants.
Mark scheme
42Oct / Nov 2017 · Paper 12 · Q19Also set in Oct / Nov 2017 Paper 11Show mark scheme →
A1, 2 and 3
B1 only
C2 only
D3 only
Mark scheme
43May / June 2017 · Paper 12 · Q14Also set in May / June 2017 Paper 11Show mark scheme →
Anegative, endothermic
Bnegative, exothermic
Cpositive, endothermic
Dpositive, exothermic
Mark scheme
44May / June 2017 · Paper 12 · Q15Also set in May / June 2017 Paper 11Show mark scheme →
A1, 2 and 3
B1 and 2 only
C2 and 3 only
D2 only
Mark scheme
45Oct / Nov 2016 · Paper 12 · Q15Show mark scheme →
Aenergy profile diagram A
Benergy profile diagram B
Cenergy profile diagram C
Denergy profile diagram D
Mark scheme
46May / June 2016 · Paper 12 · Q15Also set in May / June 2016 Paper 11Show mark scheme →
AA
BB
CC
DD
Mark scheme