Questions on Stoichiometry
Stoichiometry – Multiple-Choice Questions
1. What is stoichiometry?
A) The study of energy in reactions
B) The study of reaction mechanisms
C) The calculation of quantities in chemical reactions
D) The naming of chemical compounds
E) The identification of isotopes
2. What is required to perform a stoichiometric calculation?
A) Empirical formula
B) Balanced chemical equation
C) Boiling point
D) Ionization energy
E) Spectral lines
3. In the reaction 2H₂ + O₂ → 2H₂O, how many moles of water are produced from 3 moles of O₂?
A) 2
B) 3
C) 4
D) 6
E) 1
4. In stoichiometry, what does a mole ratio represent?
A) The mass ratio between elements
B) The ratio of moles of reactants and products
C) The pressure difference
D) The energy produced
E) The charge of ions
5. Which law supports stoichiometric relationships in reactions?
A) Law of Conservation of Mass
B) Law of Definite Proportions
C) Boyle’s Law
D) Charles’s Law
E) Law of Radioactivity
6. In the reaction N₂ + 3H₂ → 2NH₃, how many moles of H₂ are required to produce 4 moles of NH₃?
A) 2
B) 3
C) 4
D) 6
E) 8
7. What is the first step in any stoichiometry problem?
A) Measure the mass
B) Find the limiting reactant
C) Balance the chemical equation
D) Determine oxidation states
E) Identify the molecular formula
8. If 4 moles of Na react with excess Cl₂, how many moles of NaCl are formed? (2Na + Cl₂ → 2NaCl)
A) 2
B) 4
C) 1
D) 6
E) 8
9. The molar mass of water is approximately:
A) 16 g/mol
B) 18 g/mol
C) 20 g/mol
D) 14 g/mol
E) 10 g/mol
10. Which of the following is the correct mole ratio from the reaction 2Al + 3Cl₂ → 2AlCl₃?
A) 1:1
B) 2:3
C) 3:2
D) 2:1
E) 3:3
11. In a balanced equation, coefficients indicate:
A) Masses of substances
B) Volumes of solids
C) Number of atoms
D) Mole ratios
E) Atomic radii
12. In stoichiometry, converting grams to moles requires:
A) Avogadro’s number
B) Ionization energy
C) Molar mass
D) Empirical formula
E) Gas constant
13. Which quantity is conserved in all balanced chemical reactions?
A) Volume
B) Moles
C) Mass
D) Temperature
E) Pressure
14. The molar mass of CO₂ is approximately:
A) 32 g/mol
B) 44 g/mol
C) 28 g/mol
D) 40 g/mol
E) 36 g/mol
15. A limiting reactant is:
A) The one that produces the most product
B) The fastest-reacting compound
C) The one present in the smallest mass
D) The one completely used up first
E) The compound with the highest molar mass
16. What is the theoretical yield?
A) The amount of product expected based on stoichiometry
B) The amount measured in the lab
C) The actual mass of the reactant
D) The excess reactant
E) The limiting reactant
17. What is the percent yield if the theoretical yield is 40 g and the actual yield is 30 g?
A) 70%
B) 75%
C) 80%
D) 90%
E) 85%
18. If 2.0 mol of A reacts with 1.0 mol of B to produce AB₂, which is the limiting reactant?
A) A
B) B
C) AB₂
D) Both A and B
E) Cannot determine
19. Which is NOT a typical unit used in stoichiometric calculations?
A) Grams
B) Moles
C) Atoms
D) Liters
E) Joules
20. The number 6.022 × 10²³ is known as:
A) Gas constant
B) Planck’s constant
C) Avogadro’s number
D) Mass number
E) Empirical ratio
21. In the equation CH₄ + 2O₂ → CO₂ + 2H₂O, how many moles of water form from 1 mole of CH₄?
A) 1
B) 2
C) 3
D) 0.5
E) 4
22. What is molar mass used for in stoichiometry?
A) To calculate volume
B) To convert between moles and grams
C) To balance equations
D) To measure energy
E) To determine color
23. What is the mole ratio between Ca and CaCl₂ in the reaction Ca + Cl₂ → CaCl₂?
A) 1:1
B) 2:1
C) 1:2
D) 2:2
E) 3:1
24. If 36 g of H₂O are formed, how many moles is that? (Molar mass = 18 g/mol)
A) 1
B) 2
C) 3
D) 4
E) 0.5
25. What is the molar mass of NaCl?
A) 22.99 g/mol
B) 58.44 g/mol
C) 35.45 g/mol
D) 40.00 g/mol
E) 60.00 g/mol
26. Which of the following is required to determine the limiting reactant?
A) Balanced equation and actual masses
B) Reaction rate
C) Boiling point
D) Solubility rules
E) Molecular geometry
27. The reactant that remains after a chemical reaction has completed is called:
A) Limiting reactant
B) Theoretical reactant
C) Excess reactant
D) Reacted compound
E) Product reactant
28. The amount of product formed from the limiting reactant is called:
A) Actual yield
B) Excess yield
C) Theoretical yield
D) Percent yield
E) Stoichiometric mass
29. In stoichiometry, the conversion factor between moles of two substances comes from:
A) Atomic numbers
B) The balanced equation
C) Temperature
D) Solubility chart
E) Lewis structure
30. In the reaction 2Fe + 3Cl₂ → 2FeCl₃, how many moles of FeCl₃ are made from 4 moles of Fe?
A) 1
B) 2
C) 3
D) 4
E) 6
- Questions on Conversions Between Mass and Number of Particles
- Questions on Conversions Between Moles and Gas Volume
- Questions on Molar Mass
Answers with Explanations
1. C – Stoichiometry involves calculating the quantities in chemical reactions.
2. B – A balanced equation is essential to determine mole ratios.
3. D – 1 mol O₂ yields 2 mol H₂O, so 3 mol → 6 mol.
4. B – Mole ratio is from coefficients in a balanced equation.
5. A – Mass is conserved in all chemical reactions.
6. D – 2 mol NH₃ requires 3 mol H₂ → 4 mol NH₃ needs 6 mol H₂.
7. C – Always balance the equation first.
8. B – From 2Na → 2NaCl, so 4 mol Na → 4 mol NaCl.
9. B – 2(1.01) + 16.00 = ~18 g/mol.
10. B – Coefficients show a 2:3 ratio of Al:Cl₂.
11. D – Coefficients represent mole ratios.
12. C – Use molar mass to convert grams ↔ moles.
13. C – Mass is always conserved.
14. B – C = 12.01, O = 2×16.00 = 44 g/mol.
15. D – The reactant that’s completely used up.
16. A – The expected amount of product.
17. B – (30/40) × 100 = 75%.
18. B – B is limiting; 1 mol B makes only 0.5 mol AB₂.
19. E – Joules measure energy, not typically stoichiometry.
20. C – Number of particles in 1 mol.
21. B – 1 mol CH₄ makes 2 mol H₂O.
22. B – Molar mass is used to convert between grams and moles.
23. A – 1 mol Ca → 1 mol CaCl₂.
24. B – 36 ÷ 18 = 2 mol.
25. B – Na (22.99) + Cl (35.45) = 58.44 g/mol.
26. A – Masses and balanced equation are needed.
27. C – The excess reactant is left over.
28. C – Based on stoichiometry, from limiting reactant.
29. B – Balanced equations provide mole ratios.
30. D – 2 mol Fe → 2 mol FeCl₃, so 4 mol → 4 mol FeCl₃.
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