What is the general equation for the reaction between an alkane and a halogen?

Alkane + halogen ➔ halogenoalkane + hydrogen halide


For example, hexane + bromine ➔ bromohexane + hydrogen bromide. The symbol equation for this reaction is: C6H14 + Br2 ➔ C6H13Br + HBr

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State and explain the conditions are required for alkane molecules to undergo reactions with halogens?

Alkanes react with halogens when exposed to ultraviolet (UV) light.

The energy from the UV light breaks the halogen-halogen bond to initiate the reaction.

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What type of reaction occurs when alkanes react with halogens?

Free radical substitution

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What is the equation for the initiation step in the reaction between methane and chlorine?

Cl2 ➔ Cl• + Cl•


In the initation step, two free radicals are produced.

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What type of bond fission (homolytic or heterolytic) occurs during the initiation step of free radical substitution reactions?

Homolytic fission

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How do the relative amounts of chlorine and methane present determine the identity and ratio of products produced in the reaction between methane and chlorine?

If methane is in excess, more chloromethane (CH3Cl) will be produced.

If chlorine is in excess, further substitutions of H with Cl may take place which will form dichloromethane (CH2Cl2), trichloromethane (CHCl3), and tetrachloromethane (CCl4).

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Give three equations for possible termination steps in the reaction between methane and chlorine.

Cl• + Cl• ➔ Cl2

CH3• + CH3• ➔ C2H6

Cl• + CH3• ➔ CH3Cl


In the termination step, two free radicals combine to produce a single molecule.

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Give two equations for possible propagation steps in the reaction between methane and chlorine.

Cl• + CH4 ➔ HCl + CH3•

CH3• + Cl2 ➔ CH3Cl + Cl•


In the propagation step, a free radical reacts to produce another free radical.

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Describe the steps in a free radical reaction.

Free radical reactions involve 3 steps:

  1. Initiation (formation of free radicals).
  2. Propagation (repeated reactions that regenerate more free radicals).
  3. Termination (when two free radicals combine to form a stable product).

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