What is meant by the term reaction mechanism?

A reaction mechanism is a step-by-step description of how a chemical reaction takes place, showing the movement of electrons and the formation of intermediate species.

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What is the difference between heterolytic and homolytic fission?

Heterolytic fission involves one (more electronegative) atom taking both electrons from a covalent bond, forming a positive ion and a negative ion.

Homolytic fission results in each bonded atom taking one electron, forming two radicals, each with an unpaired electron.

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What does a curly arrow represent in a reaction mechanism?

The movement an electron pair, showing how a bond is broken or formed during a chemical reaction.

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What is a substitution reaction?

In a substitution reaction, an atom or group of atoms is replaced by a different atom or group of atoms in a molecule.


CH4 + Cl2 ➔ CH3Cl + HCl is an example of a substitution reaction.

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What is the mechanism for the reaction above?

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Explain the meaning of [O] in chemical equations.

[O] represents an oxygen atom from an oxidising agent.


For example, C2H5OH + 2[O] ➔ CH3COOH + H2O represents the oxidation of ethanol.

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Explain the meaning of [H] in chemical equations.

[H] represents a hydrogen atom from an reducing agent.


For example, CH3COCH3 + 2[H] ➔ CH3CH(OH)CH3 represents the reduction of propanone.

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