BMST Chemical Reactions and Stoichiometry 2 — Questions and Answers
Question 1: In the reaction 2H₂ + O₂ → 2H₂O, how many moles of water are produced from 4 moles of H₂?
- 2 moles
- 4 moles (Correct answer)
- 6 moles
- 8 moles
Correct answer: 4 moles
The molar ratio of H₂ to H₂O is 1:1, so 4 moles of H₂ produce 4 moles of H₂O.
Question 2: Which type of reaction involves a single compound breaking down into two or more simpler substances?
- Synthesis
- Decomposition (Correct answer)
- Single replacement
- Combustion
Correct answer: Decomposition
Decomposition reactions break one compound into simpler products, such as 2H₂O → 2H₂ + O₂.
Question 3: What is the molar mass of CO₂? (C=12, O=16)
- 28 g/mol
- 40 g/mol
- 44 g/mol (Correct answer)
- 56 g/mol
Correct answer: 44 g/mol
CO₂ has one carbon (12) and two oxygens (2×16=32), giving 12+32=44 g/mol.
Question 4: In a chemical equation, what does the law of conservation of mass require?
- Products weigh more than reactants
- The number of atoms on both sides must be equal (Correct answer)
- Energy must be released
- All coefficients must be equal
Correct answer: The number of atoms on both sides must be equal
Conservation of mass means atoms are neither created nor destroyed, so both sides must have the same number of each type of atom.
Question 5: How many grams of NaCl (molar mass = 58.5 g/mol) are in 2 moles of NaCl?
- 29.25 g
- 58.5 g
- 117 g (Correct answer)
- 175.5 g
Correct answer: 117 g
Mass = moles × molar mass = 2 × 58.5 = 117 g.
Question 6: Which of the following is an example of a synthesis reaction?
- CaCO₃ → CaO + CO₂
- 2Na + Cl₂ → 2NaCl (Correct answer)
- Fe + CuSO₄ → FeSO₄ + Cu
- CH₄ + 2O₂ → CO₂ + 2H₂O
Correct answer: 2Na + Cl₂ → 2NaCl
A synthesis reaction combines two or more substances into one product; 2Na + Cl₂ → 2NaCl is a classic example.
Question 7: If 10 g of hydrogen reacts with excess oxygen, and the molar mass of H₂ is 2 g/mol, how many moles of H₂ are present?
- 2 moles
- 5 moles (Correct answer)
- 10 moles
- 20 moles
Correct answer: 5 moles
Moles = mass ÷ molar mass = 10 g ÷ 2 g/mol = 5 moles.
BMST Chemical Reactions and Stoichiometry 2
In the reaction 2H₂ + O₂ → 2H₂O, how many moles of water are produced from 4 moles of H₂?