6.2.2 Energy Changes & Reversible Reactions

Energy Changes in Reversible Reactions:

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In reversible reactions, the energy changes in the forward and backward reactions are opposing. This means that if the forward reaction is exothermic, the backward reaction will be endothermic, and vice versa.

Exothermic vs. Endothermic Reactions:

Exothermic Reaction: A reaction that transfers energy to its surroundings, usually in the form of heat. This occurs when more energy is released during the formation of bonds in the products than is absorbed to break the bonds in the reactants.
Endothermic Reaction: A reaction that absorbs energy from its surroundings. This occurs when more energy is required to break the bonds in the reactants than is released during the formation of bonds in the products.

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Example: Formation of Hydrogen Iodide (HI):

Forward Reaction: The reaction of hydrogen gas ( $H_2$ ) and iodine vapour ( $I_2$ ) to form hydrogen iodide ( $H_I$ ) is exothermic. Reason: More energy is released in forming the H–I bonds than is absorbed in breaking the H–H and I–I bonds.
Backward Reaction: The reverse reaction, where HI decomposes back into $H_2$ and $I_2$ , is endothermic. Reason: More energy is needed to break the H–I bonds in HI than is released in forming H–H and I–I bonds.

General Principle:

The energy change of the reverse reaction will always be the opposite of that in the forward reaction:
- If the forward reaction is endothermic, the backward reaction will be exothermic.
- If the forward reaction is exothermic, the backward reaction will be endothermic.

Energy Changes & Reversible Reactions Simplified Revision Notes for GCSE AQA Chemistry Combined Science

6.2.2 Energy Changes & Reversible Reactions

Energy Changes in Reversible Reactions:

Exothermic vs. Endothermic Reactions:

General Principle:

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