Reversible Reactions
Chemistry: Edexcel IGCSE, topic 14.3.1
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 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.
Example - haber process
- The formation of ammonia during the Haber process is a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas).
- The Haber process is carried out at 450°C, with a pressure of 200 atmospheres, and an iron catalyst.
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?