Chemical Reactions, Acids, Bases and Salts
Reaction types
You must recognise and write equations for common reactions: combustion, oxidation, neutralisation, displacement, decomposition and thermal decomposition. Balance symbol equations so atoms are conserved. A trap is forgetting state symbols or leaving an unbalanced equation.
Rates of reaction
Rate increases with higher temperature, higher concentration, larger surface area and catalysts. Explain each using collision theory: more frequent or more energetic collisions between particles. A trap is saying a catalyst is used up; it is not.
Acids, bases and salts
Acids produce hydrogen ions in solution; bases neutralise acids; alkalis are soluble bases. Know the pH scale and indicators. Acid plus metal gives salt plus hydrogen; acid plus carbonate gives salt plus water plus carbon dioxide; acid plus base gives salt plus water. Learn the tests for hydrogen, carbon dioxide and oxygen.
Worked example
Neutralise hydrochloric acid with sodium hydroxide. Word equation: hydrochloric acid + sodium hydroxide → sodium chloride + water. Symbol equation: HCl + NaOH → NaCl + H₂O. Check that each side has the same number of each atom.
Practical rule of thumb
When naming a salt, take the metal from the base and the second part from the acid: hydrochloric gives chlorides, sulfuric gives sulfates, nitric gives nitrates.