AP Chemistry: Chemical Reactions & Stoichiometry 3 — Questions and Answers
Question 1: Which type of reaction is 2H2O2 -> 2H2O + O2?
- Synthesis
- Decomposition (Correct answer)
- Single replacement
- Combustion
Correct answer: Decomposition
One compound breaks down into two simpler products, defining decomposition.
Question 2: In a limiting reactant problem, 3 mol H2 react with 2 mol N2 to form NH3 (N2 + 3H2 -> 2NH3). Which is limiting?
- N2
- H2 (Correct answer)
- Neither, both exact
- NH3
Correct answer: H2
3 mol H2 only needs 1 mol N2, but each requires 3 mol H2 per N2; H2 runs out first making it limiting.
Question 3: What is the empirical formula of a compound that is 40.0% C, 6.7% H, and 53.3% O by mass?
- CH2O (Correct answer)
- C2H4O2
- CHO
- C2H6O
Correct answer: CH2O
Moles give a 1:2:1 C:H:O ratio, so the empirical formula is CH2O.
Question 4: How many grams are in 0.250 mol of NaCl (molar mass 58.44 g/mol)?
- 233.8 g
- 14.6 g (Correct answer)
- 29.2 g
- 58.4 g
Correct answer: 14.6 g
0.250 mol x 58.44 g/mol = 14.6 g.
Question 5: Which is the correctly balanced equation for the combustion of methane?
- CH4 + O2 -> CO2 + H2O
- CH4 + 2O2 -> CO2 + 2H2O (Correct answer)
- CH4 + 3O2 -> CO2 + 2H2O
- 2CH4 + O2 -> 2CO2 + H2O
Correct answer: CH4 + 2O2 -> CO2 + 2H2O
CH4 + 2O2 -> CO2 + 2H2O balances all C, H, and O atoms.
Question 6: At STP, what volume does 2.00 mol of an ideal gas occupy?
- 22.4 L
- 44.8 L (Correct answer)
- 11.2 L
- 67.2 L
Correct answer: 44.8 L
Each mole occupies 22.4 L at STP, so 2.00 mol is 44.8 L.
Question 7: What is the oxidation number of sulfur in SO4^2-?
- +2
- +4
- +6 (Correct answer)
- -2
Correct answer: +6
Four oxygens at -2 total -8; the ion is -2, so sulfur must be +6.
AP Chemistry: Chemical Reactions & Stoichiometry 3
Which type of reaction is 2H2O2 -> 2H2O + O2?