BMST Chemical Reactions and Stoichiometry 4 — Questions and Answers
Question 1: In stoichiometry, a mole ratio is obtained from:
- The mass of the reactants
- The coefficients of a balanced chemical equation (Correct answer)
- The atomic numbers of the elements
- The temperature of the reaction
Correct answer: The coefficients of a balanced chemical equation
Mole ratios come directly from the coefficients in a balanced equation and are used to convert between moles of different substances.
Question 2: Which symbol in a chemical equation indicates that a gas is produced?
- (s)
- (l)
- (g) or ↑ (Correct answer)
- (aq)
Correct answer: (g) or ↑
The symbol (g) or an upward arrow (↑) indicates a gaseous product is released from the reaction.
Question 3: For the reaction N₂ + 3H₂ → 2NH₃, if 6 moles of H₂ are used, how many moles of NH₃ are produced?
- 2 moles
- 4 moles (Correct answer)
- 6 moles
- 8 moles
Correct answer: 4 moles
The ratio of H₂ to NH₃ is 3:2, so 6 moles H₂ × (2 mol NH₃ / 3 mol H₂) = 4 moles NH₃.
Question 4: What does a catalyst do in a chemical reaction?
- Increases the amount of product formed
- Speeds up the reaction without being consumed (Correct answer)
- Is used up during the reaction
- Raises the activation energy required
Correct answer: Speeds up the reaction without being consumed
A catalyst lowers activation energy and speeds up a reaction but is not consumed and does not change the products.
Question 5: Which of the following correctly represents a precipitation reaction?
- Na + Cl₂ → NaCl
- AgNO₃ + NaCl → AgCl↓ + NaNO₃ (Correct answer)
- H₂ + O₂ → H₂O
- CaCO₃ → CaO + CO₂
Correct answer: AgNO₃ + NaCl → AgCl↓ + NaNO₃
When AgNO₃ and NaCl solutions are mixed, AgCl forms as an insoluble precipitate (↓) that settles out.
Question 6: The empirical formula of a compound shows:
- The actual number of each atom in one molecule
- The simplest whole-number ratio of atoms in the compound (Correct answer)
- The three-dimensional shape of the molecule
- The total molar mass of the compound
Correct answer: The simplest whole-number ratio of atoms in the compound
The empirical formula gives the simplest ratio of atoms; for example, H₂O₂ has the empirical formula HO.
Question 7: How many grams of O₂ (molar mass = 32 g/mol) are needed to produce 88 g of CO₂ (molar mass = 44 g/mol) from the reaction C + O₂ → CO₂?
- 32 g
- 44 g
- 64 g (Correct answer)
- 88 g
Correct answer: 64 g
88 g CO₂ ÷ 44 g/mol = 2 moles CO₂; ratio is 1:1, so 2 moles O₂ × 32 g/mol = 64 g O₂.
BMST Chemical Reactions and Stoichiometry 4
In stoichiometry, a mole ratio is obtained from: