The Direction of a Chemical Reaction

  • Some reactions go to completion, where the reactants are used up to form the product molecules and the reaction stops when the reactants have been exhausted.
  • In reversible reactions, the product molecules can themselves react with each other or decompose and form the reactant molecules again.
  • It is said that the reaction can occur in both directions: the forward reaction (which forms the products) and the reverse direction (which forms the reactants).
  • When writing chemical equations for reversible reactions, two arrows are used to indicate the forward and reverse reactions.
  • Each one is drawn with just half an arrowhead – the top one points to the right, and the bottom one points to the left.
  • An important example is reaction for the Haber Process which is the production of ammonia from hydrogen and nitrogen:

N2 + 3H2 ⇌ 2NH3

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.