Questions on Balancing Chemical Equations
Multiple-Choice Questions: Balancing Chemical Equations
1. Why must chemical equations be balanced?
A) To reduce the number of products
B) To follow the law of gravity
C) To conserve mass and atoms
D) To make equations simpler
E) To show energy flow
2. Which of the following is a balanced equation?
A) H₂ + O₂ → H₂O
B) 2H₂ + O₂ → 2H₂O
C) H₂ + O₂ → 2H₂O
D) H₂ + ½O₂ → H₂O
E) H₂ + O → H₂O
3. What is the coefficient for O₂ in this balanced equation: _C₃H₈ + _O₂ → _CO₂ + _H₂O?
A) 3
B) 4
C) 5
D) 2
E) 6
**4. Which number must be placed before Al in this equation to balance it?
_Al + Fe₂O₃ → Al₂O₃ + Fe**
A) 1
B) 2
C) 3
D) 4
E) 5
5. Which equation below is unbalanced?
A) Zn + 2HCl → ZnCl₂ + H₂
B) Na + Cl₂ → 2NaCl
C) 2Mg + O₂ → 2MgO
D) H₂ + O₂ → H₂O
E) C + O₂ → CO₂
6. In balancing the equation N₂ + H₂ → NH₃, what coefficients are needed?
A) 1, 1, 1
B) 1, 2, 1
C) 1, 3, 2
D) 2, 3, 2
E) 3, 2, 1
7. What is the balanced form of: Ca + H₂O → Ca(OH)₂ + H₂?
A) Ca + H₂O → Ca(OH)₂ + H₂
B) Ca + 2H₂O → Ca(OH)₂ + H₂
C) 2Ca + 2H₂O → 2Ca(OH)₂ + H₂
D) 2Ca + H₂O → 2Ca(OH)₂ + H₂
E) Ca + H₂O → CaOH + H₂
8. In a balanced equation, the total number of atoms of each element...
A) Must be less on the product side
B) Must be more on the product side
C) Can be unequal
D) Must be the same on both sides
E) Can be zero
9. Which coefficient for HCl balances this reaction: CaCO₃ + _HCl → CaCl₂ + CO₂ + H₂O?
A) 1
B) 2
C) 3
D) 4
E) 5
10. What is the balanced equation for: Al + HCl → AlCl₃ + H₂?
A) Al + HCl → AlCl₃ + H₂
B) 2Al + 3HCl → 2AlCl₃ + 3H₂
C) 2Al + 6HCl → 2AlCl₃ + 3H₂
D) Al + 6HCl → AlCl₃ + 3H₂
E) 2Al + 6HCl → AlCl₃ + 2H₂
11. Which of these equations is correctly balanced?
A) Fe + O₂ → Fe₂O₃
B) 4Fe + 3O₂ → 2Fe₂O₃
C) Fe + O₂ → 2FeO
D) 2Fe + O₂ → 2FeO₃
E) 3Fe + 2O₂ → Fe₃O₄
12. To balance C₂H₆ + O₂ → CO₂ + H₂O, what coefficient is in front of O₂?
A) 3
B) 3.5
C) 7
D) 2
E) 5
13. In the reaction: KClO₃ → KCl + O₂, what is the correct balanced form?
A) KClO₃ → KCl + O₂
B) 2KClO₃ → 2KCl + 3O₂
C) KClO₃ → 2KCl + O₂
D) 2KClO₃ → KCl + 3O₂
E) KClO₃ → KCl + 2O₂
14. What is the first step in balancing a chemical equation?
A) Add subscripts
B) Add charges
C) Write formulas for all reactants and products
D) Change products to reactants
E) Change atoms
15. The small numbers in chemical formulas (e.g., H₂O) are called:
A) Coefficients
B) Subscripts
C) Oxidation states
D) Charges
E) Balancers
16. In balancing: Na + H₂O → NaOH + H₂, what is the coefficient for Na?
A) 1
B) 2
C) 3
D) 4
E) 0
17. A balanced equation for the combustion of methane (CH₄) is:
A) CH₄ + 2O₂ → CO₂ + 2H₂O
B) CH₄ + O₂ → CO + H₂O
C) 2CH₄ + O₂ → 2CO₂ + H₂O
D) CH₄ + 2O₂ → 2CO₂ + 2H₂
E) CH₄ + 2O₂ → C + 2H₂O
18. The equation Na₂CO₃ + HCl → NaCl + H₂O + CO₂ is balanced when HCl has what coefficient?
A) 1
B) 2
C) 3
D) 4
E) 5
19. Balancing: Fe + CuSO₄ → FeSO₄ + Cu requires how many atoms of Fe?
A) 1
B) 2
C) 3
D) 0
E) 4
20. Which of these is the correct balanced form of: NH₃ + O₂ → NO + H₂O?
A) NH₃ + O₂ → NO + H₂O
B) 2NH₃ + 2O₂ → 2NO + 3H₂O
C) 4NH₃ + 3O₂ → 4NO + 6H₂O
D) 4NH₃ + 5O₂ → 4NO + 6H₂O
E) 4NH₃ + 4O₂ → 4NO + 3H₂O
Answer Key with Explanations
1. C – Balancing ensures the conservation of mass and atoms.
2. B – 2H₂ + O₂ → 2H₂O is correctly balanced.
3. C – Propane combustion: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.
4. D – 2Al + Fe₂O₃ → Al₂O₃ + 2Fe.
5. D – H₂ + O₂ → H₂O is unbalanced.
6. C – Balanced as: N₂ + 3H₂ → 2NH₃.
7. B – Ca + 2H₂O → Ca(OH)₂ + H₂ is correct.
8. D – Atom counts must match on both sides of the equation.
9. B – 2HCl are needed: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O.
10. C – Balanced as: 2Al + 6HCl → 2AlCl₃ + 3H₂.
11. B – 4Fe + 3O₂ → 2Fe₂O₃ is balanced.
12. C – Full reaction: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O.
13. B – 2KClO₃ → 2KCl + 3O₂ is balanced.
14. C – First step: write correct formulas for reactants/products.
15. B – Subscripts show the number of atoms in a molecule.
16. B – Balanced: 2Na + 2H₂O → 2NaOH + H₂.
17. A – CH₄ + 2O₂ → CO₂ + 2H₂O is correct combustion.
18. B – Balanced: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂.
19. A – 1Fe is sufficient for 1CuSO₄ in single replacement.
20. D – Correctly balanced: 4NH₃ + 5O₂ → 4NO + 6H₂O.
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