Vidaara.orgClass 10 · Chemistry
CodeVID-C10-01-T1-01
Assignment — Chemical Equations & Balancing
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The substances formed in a chemical reaction are called:
- A.reactants
- B.products
- C.catalysts
- D.mixtures
2.
To balance an equation we change the:
- A.subscripts
- B.chemical symbols
- C.coefficients
- D.arrow direction
3.
The state symbol for a gas is:
- A.(s)
- B.(l)
- C.(g)
- D.(aq)
4.
On burning, magnesium ribbon forms a white powder of:
- A.magnesium
- B.magnesium oxide
- C.magnesium nitride only
- D.carbon
5.
The balanced equation for the burning of methane is:
- A.CH4 + O2 → CO2 + H2O
- B.CH4 + 2O2 → CO2 + 2H2O
- C.CH4 + O2 → CO2 + 2H2O
- D.2CH4 + O2 → 2CO2 + H2O
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
State the law of conservation of mass and explain how it relates to balancing an equation.
7.
Balance: H2 + N2 → NH3.
8.
List any three observations that tell you a chemical reaction has taken place.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Balance and add state symbols: barium chloride + sodium sulphate → barium sulphate + sodium chloride.
10.
Balance: Pb(NO3)2 → PbO + NO2 + O2.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Write the balanced chemical equation, with state symbols, for the reactions of (a) sodium with water and (b) the action of heat on calcium carbonate, and explain the steps you used to balance equation (a).
Answer Key
Section A — Multiple Choice Questions
- (B) products
- (C) coefficients
- (C) (g)
- (B) magnesium oxide
- (B) CH4 + 2O2 → CO2 + 2H2O
Section B — Short Answer (2 marks)
- Mass can neither be created nor destroyed in a chemical reaction, so the total mass of reactants equals that of products; this means each element must have equal atoms on both sides, which is why equations are balanced.
- N2 + 3H2 → 2NH3 (2 N and 6 H on each side).
- Any three of: change in colour, change in state, evolution of a gas, formation of a precipitate, change in temperature.
Section C — Short Answer (3 marks)
- BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq); BaSO₄ is the white precipitate, hence (s).
- 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ (2 Pb, 4 N, 12 O on each side).
Section D — Long Answer (5 marks)
- (a) 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g). Steps: write the skeletal equation Na + H₂O → NaOH + H₂; balance Na by 2 on both sides; this gives 4 H on the left, so make 2NaOH (2 H) plus H₂ (2 H) on the right; oxygen is then 2 = 2, so the equation is balanced. (b) CaCO₃(s) → CaO(s) + CO₂(g), a thermal decomposition.
Generated by Vidaara.org · Assignment VID-C10-01-T1-01 · vidaara.org