BMST Chemical Reactions and Stoichiometry 5 — Questions and Answers
Question 1: In a single replacement reaction, what determines whether the reaction will occur?
- The temperature of the solution
- Whether the replacing element is more reactive than the one it displaces (Correct answer)
- The concentration of the solution
- Whether the compounds are ionic or covalent
Correct answer: Whether the replacing element is more reactive than the one it displaces
A single replacement reaction occurs only if the replacing element is higher on the activity series than the element it displaces.
Question 2: What is theoretical yield?
- The amount of product actually obtained from an experiment
- The maximum amount of product calculated from stoichiometry assuming complete reaction (Correct answer)
- The amount of limiting reagent consumed
- The mass of excess reagent remaining
Correct answer: The maximum amount of product calculated from stoichiometry assuming complete reaction
Theoretical yield is the calculated maximum product possible based on the limiting reagent and stoichiometry.
Question 3: Which equation is correctly balanced?
- H₂ + O₂ → H₂O
- 2H₂ + O₂ → 2H₂O (Correct answer)
- H₂ + 2O → H₂O₂
- 2H + O → H₂O
Correct answer: 2H₂ + O₂ → 2H₂O
2H₂ + O₂ → 2H₂O has 4 hydrogen atoms and 2 oxygen atoms on each side, satisfying conservation of mass.
Question 4: What is the molarity of a solution containing 2 moles of NaCl dissolved in 0.5 liters of solution?
- 0.25 M
- 1 M
- 2 M
- 4 M (Correct answer)
Correct answer: 4 M
Molarity = moles ÷ liters = 2 mol ÷ 0.5 L = 4 M.
Question 5: In the reaction 2Al + 3Cl₂ → 2AlCl₃, if 3 moles of Cl₂ are available and 4 moles of Al are available, which is the limiting reagent?
- Al, because there are more moles of it
- Cl₂, because it requires a 3:2 ratio with Al and runs out first (Correct answer)
- Neither, they are both in excess
- AlCl₃, because it is the product
Correct answer: Cl₂, because it requires a 3:2 ratio with Al and runs out first
3 moles Cl₂ can react with only 2 moles Al (ratio 3:2), leaving 2 moles Al unused; Cl₂ is the limiting reagent.
Question 6: Which of the following best describes an endothermic reaction?
- It releases heat to the surroundings
- It absorbs heat from the surroundings (Correct answer)
- It produces light as a byproduct
- It requires a catalyst to proceed
Correct answer: It absorbs heat from the surroundings
Endothermic reactions absorb energy (heat) from the surroundings, causing the surroundings to feel cooler.
Question 7: What is the coefficient of O₂ when the equation _C₃H₈ + _O₂ → _CO₂ + _H₂O is balanced?
- 3
- 4
- 5 (Correct answer)
- 6
Correct answer: 5
Balanced: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O; five O₂ molecules provide the 10 oxygen atoms needed for 3CO₂ and 4H₂O.
BMST Chemical Reactions and Stoichiometry 5
In a single replacement reaction, what determines whether the reaction will occur?