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IB Chemistry: Electron sharing reactions — Practice Questions & Answers

72 practice questions available for this topic — here are 10 with full answers and explanations.

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Practice questions with answers

1 Multiple choice · Easy

Homolytic fission of a covalent bond produces:

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WhyIn homolytic fission each atom takes one of the shared electrons, forming two radicals (species with an unpaired electron).
2 Multiple choice · Easy

The free-radical substitution of methane with chlorine requires:

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WhyUltraviolet (UV) light supplies the energy to break the Cl-Cl bond homolytically and start the reaction.
3 Multiple choice · Medium

Which equation represents the initiation step of the chlorination of methane?

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WhyInitiation is the homolytic splitting of $\text{Cl}_{2}$ by UV light into two chlorine radicals: $\text{Cl}_{2} \rightarrow 2\text{Cl}\bullet$.
4 Multiple choice · Medium

A termination step in a radical chain reaction is one in which:

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WhyTermination removes radicals by combining two of them to form a stable molecule, e.g. $\text{CH}_{3}\bullet + \text{Cl}\bullet \rightarrow \text{CH}_{3}\text{Cl}$.
5 Multiple choice · Medium

What are the products of the monochlorination (single substitution) of methane?

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WhyOne H is replaced by Cl, giving chloromethane and hydrogen chloride: $\text{CH}_{4} + \text{Cl}_{2} \rightarrow \text{CH}_{3}\text{Cl} + \text{HCl}$.
6 Multiple choice · Hard

Which step regenerates reactive radicals so that the chain reaction can continue?

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WhyIn propagation steps a radical reacts with a molecule to form a product and a new radical, sustaining the chain, e.g. $\text{CH}_{4} + \text{Cl}\bullet \rightarrow \text{CH}_{3}\bullet + \text{HCl}$.
7 Fill in the blank · Easy

A species that contains an unpaired electron and is highly reactive is called a .

Answer: radical / free radical

WhyA free radical has an unpaired electron, usually shown with a dot, e.g. $\text{Cl}\bullet$.
8 Fill in the blank · Medium

The first step of free-radical substitution, in which UV light splits $\text{Cl}_{2}$ into radicals, is called .

Answer: initiation

WhyInitiation creates the first radicals by homolytic fission of the halogen molecule under UV light.
9 Multiple choice · Medium

Which species forms when Br2 undergoes homolytic fission in UV light?

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WhyHomolytic fission splits the bond evenly, giving two bromine radicals, each written Br with a single unpaired electron.
10 Multiple choice · Medium

When one covalent bond in CHCl2F breaks homolytically in the upper atmosphere, the weakest bond breaks. Which radical is most likely formed?

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WhyThe C-Cl bond is weakest, so a chlorine atom leaves, giving the radical with formula CHClF.

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Practise other IB Chemistry topics

Topic S1.1 (SL/HL): Introduction to the particulate nature of matter Topic S1.2 (SL/HL): The nuclear atom Topic S1.2 (HL): The nuclear atom Topic S1.3 (SL/HL): Electron configurations Topic S1.3 (HL): Electron configurations Topic S1.4 (SL/HL): Counting particles by mass: the mole Topic S1.5 (SL/HL): Ideal gases Topic S2.1 (SL/HL): The ionic model Topic S2.1 (HL): The ionic model Topic S2.2 (SL/HL): The covalent model Topic S2.2 (HL): The covalent model Topic S2.3 (SL/HL): The metallic model Topic S2.3 (HL): The metallic model Topic S2.4 (SL/HL): From models to materials Topic S2.4 (HL): From models to materials Topic S3.1 (SL/HL): The periodic table: classification of elements Topic S3.1 (HL): The periodic table: classification of elements Topic S3.2 (SL/HL): Functional groups: classification of organic compounds Topic S3.2 (HL): Functional groups: classification of organic compounds Topic R1.1 (SL/HL): Measuring enthalpy changes Topic R1.2 (SL/HL): Energy cycles in reactions Topic R1.2 (HL): Energy cycles in reactions Topic R1.3 (SL/HL): Energy from fuels Topic R1.4 (HL): Entropy and spontaneity Topic R2.1 (SL/HL): How much? The amount of chemical change Topic R2.2 (SL/HL): How fast? The rate of chemical change Topic R2.2 (HL): How fast? The rate of chemical change Topic R2.3 (SL/HL): How far? The extent of chemical change Topic R2.3 (HL): How far? The extent of chemical change Topic R3.1 (SL/HL): Proton transfer reactions Topic R3.1 (HL): Proton transfer reactions Topic R3.2 (SL/HL): Electron transfer reactions Topic R3.2 (HL): Electron transfer reactions Topic R3.4 (SL/HL): Electron-pair sharing reactions Topic R3.4 (HL): Electron-pair sharing reactions