RPAL Mole Ratios 1 — Questions and Answers
Question 1: What is a mole ratio in a chemical reaction?
- The ratio of moles of one substance to moles of another, derived from the balanced equation (Correct answer)
- The ratio of masses of reactants to products
- The number of moles of product per liter of solution
- The ratio of molar masses of reactants
Correct answer: The ratio of moles of one substance to moles of another, derived from the balanced equation
Mole ratios come directly from the stoichiometric coefficients in the balanced equation and relate moles of any two substances in the reaction.
Question 2: In the balanced equation 2H₂ + O₂ → 2H₂O, what is the mole ratio of H₂ to H₂O?
- 2:2 (or 1:1) (Correct answer)
- 2:1
- 1:2
- 1:1 only if masses are equal
Correct answer: 2:2 (or 1:1)
The coefficients 2 (H₂) and 2 (H₂O) give a mole ratio of 2:2, which simplifies to 1:1.
Question 3: For N₂ + 3H₂ → 2NH₃, what is the mole ratio of H₂ to NH₃?
- 3:2 (Correct answer)
- 1:2
- 2:3
- 3:1
Correct answer: 3:2
The coefficients are 3 for H₂ and 2 for NH₃, giving a 3:2 mole ratio.
Question 4: Why must an equation be balanced before using mole ratios?
- Because mole ratios are derived from stoichiometric coefficients, which are only correct in a balanced equation (Correct answer)
- Because unbalanced equations have no products
- Because balancing changes the identity of the substances
- Because mole ratios only apply to gases
Correct answer: Because mole ratios are derived from stoichiometric coefficients, which are only correct in a balanced equation
Stoichiometric coefficients in a balanced equation reflect the law of conservation of mass; incorrect coefficients give wrong mole ratios.
Question 5: Using the mole ratio, if you have 4 mol H₂ reacting via 2H₂ + O₂ → 2H₂O, how many moles of O₂ are needed?
- 2 mol O₂ (Correct answer)
- 4 mol O₂
- 1 mol O₂
- 8 mol O₂
Correct answer: 2 mol O₂
The H₂:O₂ mole ratio is 2:1, so 4 mol H₂ requires 4 × (1/2) = 2 mol O₂.
Question 6: For 4Fe + 3O₂ → 2Fe₂O₃, what is the mole ratio of Fe to Fe₂O₃?
- 4:2 (or 2:1) (Correct answer)
- 1:1
- 3:2
- 4:3
Correct answer: 4:2 (or 2:1)
The coefficients 4 (Fe) and 2 (Fe₂O₃) give a mole ratio of 4:2, simplifying to 2:1.
RPAL Mole Ratios 1
What is a mole ratio in a chemical reaction?