State the law of conservation of mass.

State two points of information necessary to write the molecular formula of a compound.

Write balanced chemical equations for the following word equations:

1. Iron + Chlorine ⟶ Iron(III) chloride

2. Magnesium + dil. sulphuric acid ⟶ Magnesium sulphate + hydrogen

3. Magnesium + oxygen ⟶ Magnesium oxide

4. Calcium oxide + water ⟶ Calcium hydroxide

5. Sodium + Chlorine ⟶ Sodium chloride

What information do you get from the following chemical equations?

(a) Zn(s) + 2HCl (dil) ⟶ ZnCl₂ (aq) + H₂ (g)

(b) N₂(g) + 3H₂(g) $\xleftrightharpoons[\text{400-500°C 200-900 atm}]{\text{Fe (catalyst)/Mo (promoter)}}$ 2NH₃(g) + Heat