plumiCombustion, halogenation and free radical substitution: Edexcel International A Level Chemistry questions
Edexcel International A Level Chemistry past-paper questions on 4.B.5 Combustion, halogenation and free radical substitution, 2019–2025, with mark schemes and examiner’s reports where available.
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Q20(b)(i)
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All 54 questions on Combustion, halogenation and free radical substitution, as a list
- June 2025, AS Unit 1, Q20(b)(i) (1 mark): State what is meant by complete combustion. (1)
- June 2025, AS Unit 1, Q20(b)(ii) (2 marks): Write a balanced equation for the complete combustion of dodecane, C12H26 . Include state symbols. (2)
- June 2025, AS Unit 1, Q22(a) (1 mark): Name the type and mechanism for the reaction between halogens and alkanes. (1)
- June 2025, AS Unit 1, Q22(b)(i) (2 marks): Give the equation for the initiation step. Include appropriate arrows and electrons. (2)
- June 2025, AS Unit 1, Q22(b)(ii) (2 marks): Give an equation for each of the first two propagation steps. (2) First propagation step Second propagation step
- June 2025, AS Unit 1, Q22(b)(iii) (1 mark): Give the equation for the termination step to form an alkane. (1)
- January 2025, AS Unit 1, Q25(a)(i) (1 mark): Name the mechanism and type of this reaction. (1)
- January 2025, AS Unit 1, Q25(a)(ii) (1 mark): Give the essential condition for Step 1 to occur. (1)
- January 2025, AS Unit 1, Q25(a)(iii) (1 mark): Name the type of step illustrated by Step 3. (1)
- January 2025, AS Unit 1, Q25(a)(iv) (4 marks): A different type of step, other than the ones shown, also occurs in the reaction. Describe this type of step, including two possible examples which might occur
- October 2024, AS Unit 1, Q13 (1 mark): Cycloalkanes undergo free radical substitution reactions by the same mechanism as methane. Three isomeric cycloalkanes are shown. Isomer X Isomer Y Isomer Z Whi
- October 2024, AS Unit 1, Q18(c)(i) (1 mark): Write the equation for the complete combustion of isooctane. State symbols are not required. (1)
- October 2024, AS Unit 1, Q18(d)(i) (1 mark): State the type and mechanism of this reaction. (1)
- October 2024, AS Unit 1, Q18(d)(ii) (1 mark): Give the essential condition required. (1)
- January 2024, AS Unit 1, Q19(b)(i) (2 marks): Show the initiation step of this reaction. Include appropriate arrows and the conditions necessary for this step. (2)
- January 2024, AS Unit 1, Q19(b)(ii) (2 marks): Using your answer to (b)(i), state what is meant by the terms homolytic and free radical. (2) homolytic free radical
- January 2024, AS Unit 1, Q19(b)(iii) (1 mark): Suggest why this method has limited use in the synthesis of organic compounds. (1)
- October 2023, AS Unit 1, Q19(d)(i) (2 marks): Describe the role of the ultraviolet light in the initiation step of this reaction. (2)
- October 2023, AS Unit 1, Q19(d)(ii) (2 marks): The alkane dodecane, C12H26, is formed in this reaction. Write equations for the propagation step and for the termination step for the formation of this product
- January 2023, AS Unit 1, Q18 (1 mark): Which is not a step in the reaction of chlorine with propane in ultraviolet radiation? A C3H7· + Cl· → C3H7Cl B C3H7· + C3H7· → C6H14 C C3H7· + Cl2 → C3H7Cl + C
- January 2023, AS Unit 1, Q19 (1 mark): Why does free radical substitution have limited use in industrial chemistry? A the reactions only occur in the upper atmosphere B initiation requires ultraviole
- January 2023, AS Unit 1, Q21(b)(i) (2 marks): Write an equation for the complete combustion of heptane. Include state symbols. (2)
- October 2022, AS Unit 1, Q7(a) (1 mark): What is the role of ultraviolet radiation in the reaction? (1) A to break the Br Br bond only B to break a C H bond only C to break a C C bond only D to break b
- October 2022, AS Unit 1, Q7(b) (1 mark): One of the steps of the reaction is shown. C8H17• + Br2 → C8H17Br + Br• What is the name of this step and the type of bond breaking that takes place in the brom
- October 2022, AS Unit 1, Q7(c) (1 mark): What is the overall equation for the reaction of octane with bromine? (1) A C8H18 + Br2 → C8H16Br2 + H2 B C8H18 + Br2 → C8H17Br + HBr C C8H18 + Br2 → 2C4H9Br D
- June 2022, AS Unit 1, Q17 (1 mark): Which of these occurs in a propagation step in the reaction of methane with chlorine? A H3C Cl B H3C Cl Cl C H3C H CH3 D Cl Cl H3C H
- June 2022, AS Unit 2, Q18(a)(ii) (2 marks): Write the equation for the complete combustion of 2,2,4-trimethylpentane, using molecular formulae. State symbols are not required. (2)
- January 2022, AS Unit 1, Q10(a) (1 mark): What is the equation for the reaction? (1) A C2H6 + Br2 ® C2H4Br2 + H2 B C2H6 + Br2 ® C2H5Br + HBr C C2H6 + Br2 ® 2CH3Br D C2H6 + Br2 ® CH4 + CH2Br2
- January 2022, AS Unit 1, Q10(b) (1 mark): The ultraviolet radiation is needed for (1) A homolytic breaking of a Br–Br bond B heterolytic breaking of a Br–Br bond C homolytic breaking of a C–H bond D het
- October 2021, AS Unit 1, Q10(a) (1 mark): Which process occurs in the initiation step? (1) A Cl Cl B Cl Cl C Cl Cl D Cl Cl
- October 2021, AS Unit 1, Q10(b) (1 mark): Which of these molecules could not be formed in a termination step? (1) A C2H6 B CH3Cl C CH2Cl2 D HCl Use this space for any rough working. Anything you write i
- June 2021, AS Unit 1, Q21(a)(ii) (1 mark): Write the equation for the incomplete combustion of heptane, forming carbon monoxide and water as the only products. State symbols are not required. (1)
- June 2021, AS Unit 1, Q21(c)(i) (2 marks): State the type and mechanism of this reaction. (2)
- June 2021, AS Unit 1, Q21(c)(ii) (7 marks): Give the mechanism for the reaction to produce C7H15Cl, C14H30 and HCl as the only products. Include the name of each of the steps in your mechanism. Curly half
- January 2021, AS Unit 1, Q16(a) (1 mark): Which of these is an overall equation for this reaction? (1) A C5H8 + Br2 → C5H8Br2 B C5H10 + Br2 → C5H10Br2 C C5H10 + Br2 → C5H8Br2 + H2 D C5H10 + Br2 → C5H9Br
- January 2021, AS Unit 1, Q16(b) (1 mark): Which statement is not correct about this reaction system? (1) A only the initiation step involves homolytic bond fission B only some bromine is converted to fr
- January 2021, AS Unit 1, Q16(c) (1 mark): Which free radical is least likely to form in a propagation step in this reaction system? (1) A C5H9• B Br• C C5H8Br• D H•
- January 2021, AS Unit 1, Q16(d) (1 mark): Which alkane could be formed in a termination step in this reaction system? (1) A B C D Use this space for any rough working. Anything you write in this space w
- January 2021, AS Unit 1, Q20(a) (2 marks): Write an equation for the incomplete combustion of one mole of propene to form carbon dioxide, carbon monoxide, carbon and water as the only products. Include s
- October 2020, AS Unit 1, Q22(b)(i) (1 mark): State the essential condition necessary for this process. (1)
- October 2020, AS Unit 1, Q22(b)(ii) (2 marks): Write an equation for this fission in molecule X. Include curly half-arrows. (2)
- October 2020, AS Unit 1, Q22(b)(iii) (2 marks): Write an equation for the reaction of a chlorine free radical with a molecule of X. Curly half-arrows are not required. (2)
- October 2020, AS Unit 1, Q22(b)(iv) (2 marks): Write an equation, using displayed formulae, for a free radical formed in this sequence to give a molecule with the formula C4H4Cl6 . (2)
- October 2020, AS Unit 1, Q22(b)(v) (2 marks): State the type of reaction occurring in (b)(iv) and the name of the product with the formula C4H4Cl6 . (2)
- October 2020, Unit 5, Q4 (1 mark): Chlorine reacts with methylbenzene in the presence of ultraviolet light. Which of these is a product of this reaction? CH2Cl Cl A B Cl CH3 CH2Cl C D Cl Cl Cl Us
- January 2020, AS Unit 1, Q15 (1 mark): A pure alkane fuel is burned in air. Which substance is not a possible combustion product? A H2 B H2O C CO D CO2 Use this space for any rough working. Anything
- January 2020, AS Unit 1, Q20(b)(i) (2 marks): Draw the initiation step of this reaction, using curly half-arrows. (2)
- January 2020, AS Unit 1, Q20(b)(ii) (2 marks): Write equations for two propagation steps to show how C6H13Br is formed. Curly arrows are not required. (2)
- January 2020, AS Unit 1, Q20(b)(iii) (1 mark): Give the molecular formula of an alkane formed in a termination step in this reaction. (1)
- June 2019, AS Unit 1, Q22(b)(ii) (2 marks): Write the equation for the complete combustion of octane. State symbols are not required. (2)
- January 2019, AS Unit 1, Q21(b)(i) (1 mark): Chlorine radicals are formed in the first step in the mechanism. Cl2 o 2Cl• Name this step in the mechanism. (1)
- January 2019, AS Unit 1, Q21(b)(ii) (2 marks): Give the two propagation steps for the formation of chloroheptane. Use molecular formulae. Curly arrows are not required. (2)
- January 2019, AS Unit 1, Q21(b)(iii) (1 mark): Give the termination step which forms a hydrocarbon. (1)
- January 2019, AS Unit 1, Q21(b)(iv) (2 marks): Explain how some dichloroheptane, C7H14Cl2 , also forms during this reaction. You may include equation(s) in your answer. (2)
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