Learn to write and balance chemical equations, identify the five main types of chemical reactions, and understand oxidation and reduction.
A balanced chemical equation has the same number of atoms of each element on both sides, following the Law of Conservation of Mass — matter is neither created nor destroyed in a chemical reaction.
Balance: Mg + O₂ → MgO
2Mg + O₂ → 2MgO (2 Mg and 2 O atoms on each side)
Balance: Zn + HCl → ZnCl₂ + H₂
Zn + 2HCl → ZnCl₂ + H₂ (1 Zn, 2 H, 2 Cl on each side)
Reactions are classified by what happens to the reactants and products.
Two or more substances combine to form one product. E.g. CaO + H₂O → Ca(OH)₂
One substance breaks into two or more simpler ones. E.g. CaCO₃ → CaO + CO₂
A more reactive element displaces a less reactive one. E.g. Zn + CuSO₄ → ZnSO₄ + Cu
Two compounds exchange ions. E.g. NaOH + HCl → NaCl + H₂O
CaCO₃ → CaO + CO₂ (on heating). What type of reaction is this, and is it balanced?
Decomposition reaction; yes it's balanced — 1 Ca, 1 C, 3 O on each side
Oxidation is the gain of oxygen (or loss of hydrogen); reduction is the loss of oxygen (or gain of hydrogen). Both happen together in a redox reaction.
In 2CuO + C → 2Cu + CO₂, which substance is reduced and which is oxidized?
CuO is reduced (loses oxygen, becomes Cu); carbon is oxidized (gains oxygen, becomes CO₂)
1. Balance: Al + O₂ → Al₂O₃
2. Fe + CuSO₄ → FeSO₄ + Cu — what type of reaction is this?
3. 2KClO₃ → 2KCl + 3O₂ — what type of reaction is this?
4. AgNO₃ + NaCl → AgCl + NaNO₃ — what type of reaction is this?
5. In the reaction MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O, is MnO₂ being oxidized or reduced?