Reversible Reactions
Chemistry: AQA GCSE Higher, topic 6.2.1
Reversible Reactions
Some chemical reactions can proceed in both forwards and backwards directions. We describe these reactions as reversible.
Reversible reactions
- A + B ⇌ C + D
- The reactants (A + B) can combine to give the products (C + D).
- The products (C + D) can combine to give the reactants (A + B).
Exothermic and endothermic reactions
- If the forwards reaction is exothermic (transfers energy from reactants to the environment), the backwards reaction will be endothermic (transfers energy from the environment to the reactants).
Conservation of energy
- Energy is conserved during chemical reactions.
- The energy released/absorbed by the forward reaction will be exactly equal to the energy absorbed/released by the backward reaction.
Test yourself on Reversible Reactions
In a reversible reaction, energy cannot be lost or gained overall. Why must the amount of energy absorbed by the backward reaction equal the amount of energy released by the forward reaction?
The equation NH4Cl ⇌ NH3 + HCl shows a reversible reaction. What forms when ammonia gas reacts with hydrogen chloride gas?
A reversible reaction's backward reaction absorbs energy from the surroundings. What does this tell you about the forward reaction?
In the equilibrium NH4Cl ⇌ NH3 + HCl, suppose the forward reaction (ammonium chloride breaking down into ammonia and hydrogen chloride) is endothermic. What must be true of the backward reaction, in which ammonia and hydrogen chloride combine to re-form ammonium chloride?
In the equilibrium NH4Cl ⇌ NH3 + HCl, ammonia gas and hydrogen chloride gas are observed combining inside a sealed container to form solid ammonium chloride. Which direction of the reaction is taking place?