BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers 5 — Questions and Answers
Question 1: Which of the following describes an exothermic reaction?
- Energy is absorbed from the surroundings
- The products have more energy than the reactants
- Energy is released to the surroundings (Correct answer)
- Activation energy is not required
Correct answer: Energy is released to the surroundings
Exothermic reactions release energy to the surroundings, making the products lower in energy than the reactants.
Question 2: When balancing the equation __Fe + __O₂ → __Fe₂O₃, what are the correct coefficients?
- 2, 1, 1
- 4, 3, 2 (Correct answer)
- 2, 3, 2
- 1, 1, 2
Correct answer: 4, 3, 2
The balanced equation is 4Fe + 3O₂ → 2Fe₂O₃, conserving iron (4 atoms each side) and oxygen (6 atoms each side).
Question 3: What is the molarity of a solution containing 2 moles of NaCl dissolved in 0.5 liters of solution?
- 1 M
- 2 M
- 4 M (Correct answer)
- 0.25 M
Correct answer: 4 M
Molarity = moles of solute / liters of solution = 2 mol / 0.5 L = 4 M.
Question 4: In a single replacement reaction, Zn + CuSO₄ → ZnSO₄ + Cu, what is the driving force?
- Zinc is less reactive than copper
- Zinc is more reactive than copper and displaces it (Correct answer)
- Copper is more reactive and oxidizes zinc
- Both metals have equal reactivity
Correct answer: Zinc is more reactive than copper and displaces it
Zinc is higher on the activity series than copper, so it displaces copper from the solution.
Question 5: If 2 moles of H₂ react with 1 mole of O₂ to form water, and you start with 3 moles of H₂ and 1 mole of O₂, which is the limiting reagent?
- H₂
- O₂ (Correct answer)
- Both are limiting
- Neither is limiting
Correct answer: O₂
O₂ is the limiting reagent because 1 mol O₂ can only react with 2 mol H₂, leaving 1 mol H₂ unused.
Question 6: What is the law of conservation of mass as applied to chemical reactions?
- Mass is created during a chemical reaction
- The mass of products is less than the mass of reactants
- The total mass of reactants equals the total mass of products (Correct answer)
- Mass can be destroyed in an exothermic reaction
Correct answer: The total mass of reactants equals the total mass of products
The law of conservation of mass states that matter is neither created nor destroyed in a chemical reaction, so mass is conserved.
Question 7: How many grams of NaCl (molar mass 58.5 g/mol) are needed to make 2 moles of NaCl?
- 29.25 g
- 58.5 g
- 117 g (Correct answer)
- 234 g
Correct answer: 117 g
Mass = moles × molar mass = 2 mol × 58.5 g/mol = 117 g.
BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers 5
Which of the following describes an exothermic reaction?