State the information provided by a chemical equation. Chemical equations suffer from a number of limitations. State the main limitations of a chemical equation.

State what is a balanced equation with a relevant example. Give a reason why an equation is balanced with reference to the law of conservation of matter.

Balance the following equations:

(a) P + O₂ ⟶ P₂O₅

(b) Na₂O + H₂O ⟶ NaOH

(c) K + H₂O ⟶ KOH + H₂

(d) Fe + H₂O ⇌ Fe₃O₄ + H₂

(e) CaO + HCl ⟶ CaCl₂ + H₂O

(f) Fe + Cl₂ + FeCl₃

(g) Al + H₂O ⟶ Al₂O₃ + H₂

(h) Al + H₂SO₄ ⟶ Al₂(SO₄)₃ + H₂

(i) Fe₂O₃ + H₂ ⟶ Fe + H₂O

(j) C + H₂SO₄ ⟶ CO₂ + H₂O + SO₂

(k) Pb₃O₄ ⟶ PbO + O₂

(l) Al + O₂ ⟶ Al₂O₃

(m) NO + O₂ ⟶ NO₂

(n) ZnS + O₂ ⟶ ZnO + SO₂

(o) Pb₃O₄ + HCl ⟶ PbCl₂ + H₂O + Cl₂

(p) ZnO + NaOH ⟶ Na₂ZnO₂ + H₂O

(q) H₂S + Cl₂ ⟶ S + HCl

(r) FeCl₃ + NaOH ⟶ NaCl + Fe(OH)₃

(s) Fe₂O₃ + CO ⟶ Fe + CO₂

(t) KHCO₃ ⟶ K₂CO₃ + H₂O + CO₂

(u) CuO + NH₃ ⟶ Cu + H₂O + N₂

Complete the statements given below by filling in the blank with the correct word/s.

1. The formula of silver [I] chloride is …………… [AgCl/AgCl₂].

2. The basic unit of an element is a/an …………… [molecule/atom/ion].

3. Atom contains ………….. [neutron/nucleus], with positively charged …………… [electrons/protons] .

4. Element ………….. [calcium/lead/carbon] has the symbol derived from its Latin name 'plumbum'.

5. From the elements - He, Br, Pt & O; the element which forms a polyatomic molecule is …………… & which is liquid at room temperature is ……………

6. The valency of iron in FeO is …………… [2⁺/1⁺] of chlorine [chloride] in CaCl₂ is ………….. [1^-/2^-] and of dichromate in K₂Cr₂O₇ is ………….. [2⁺/2^-]