Chemical equations

• In a chemical reaction, at least one of the following will occur:

  • Change in state
  • Change in colour
  • Evolution of a gas
  • Change in temperature
  • Formation of a precipitate
• A chemical equation is the symbolic representation of a chemical reaction in the form of chemical formulae, signs, symbols, and directions

  • Reactant entities are on the left-hand side and product entities on the right-hand side
• Balanced chemical equation:

  • Reactants → Products
  • Total number of atoms on the LHS = Total number of atoms on the RHS
• How to balance an equation:

  • Write reactants and products
  • Balance the maximum number of a particular atom on both sides
  • Balance other atoms
• Types of reactions:

  • Combination reaction: Two or more reactants combine to form one single product
  • Exothermic reaction: Heat gets released in the reaction
  • Endothermic reaction: Heat is absorbed in the reaction
  • Decomposition reaction: A single reactant breaks into several simple products
  • Displacement reactions: A more reactive metal can displace a less reactive metal from their compounds in aqueous solutions
  • Double displacement reaction: Exchange of ions occurs between two compounds
• Precipitation reaction:

  • When the aqueous solution of two compounds react by exchanging their respective ions, forming an insoluble salt as a precipitate
• Neutralisation reaction:

  • When an acid solution reacts with a base to form only salt and water as products
• Gas-forming reaction:

  • When two compounds react and displace their ions, forming gaseous compounds or a product in the gaseous state
• Oxidation:

  • When a substance gains oxygen or loses hydrogen
• Reduction:

  • When one substance loses oxygen or gains hydrogen
• Redox:

  • Oxidation-reduction reaction