Chemistry Test Stoichiometry 2

Question 1

How many grams of water are produced when 4 grams of hydrogen gas (H₂) reacts completely with excess oxygen? (H=1, O=16)

Accepted Answer

36 g

Answer

4 g H₂ = 2 mol H₂, and 2H₂ + O₂ → 2H₂O gives 2 mol H₂O = 36 g.

Question 2

What is the percent yield if a reaction theoretically produces 50 g of product but only 38 g is actually obtained?

Accepted Answer

76%

Answer

Percent yield = (actual/theoretical) × 100 = (38/50) × 100 = 76%.

Question 3

In the reaction N₂ + 3H₂ → 2NH₃, if 6 mol of H₂ is used, how many moles of NH₃ are produced?

Accepted Answer

4 mol

Answer

6 mol H₂ × (2 mol NH₃ / 3 mol H₂) = 4 mol NH₃.

Question 4

A compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula? (C=12, H=1, O=16)

Accepted Answer

CH₂O

Answer

Dividing by atomic masses: C=40/12≈3.33, H=6.7/1=6.7, O=53.3/16≈3.33; ratio 1:2:1 gives CH₂O.

Question 5

Which quantity is conserved during a chemical reaction according to the law of conservation of mass?

Accepted Answer

Total mass of reactants and products

Answer

The law of conservation of mass states that total mass of reactants equals total mass of products.

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