Stoichiometry, at its core, is about the quantitative relationships between reactants and products in chemical reactions. Mastering stoichiometry is crucial for any aspiring chemist, and this worksheet, complete with answers, will help you build a strong foundation in this fundamental concept. We'll cover various types of stoichiometry problems, from simple mole-to-mole conversions to more complex scenarios involving limiting reactants and percent yield.
Section 1: Mole-to-Mole Conversions
Instructions: For each balanced chemical equation, determine the mole ratio between the specified reactants and products. Then, use this ratio to answer the subsequent question.
Problem 1:
2H₂ + O₂ → 2H₂O
What number of moles of water are produced from the reaction of 4 moles of hydrogen gas with excess oxygen?
Answer 1:
The mole ratio of H₂ to H₂O is 2:2, which simplifies to 1:1. Therefore, 4 moles of H₂ will produce 4 moles of H₂O.
Problem 2:
N₂ + 3H₂ → 2NH₃
How many moles of nitrogen gas are required to produce 6 moles of ammonia?
Answer 2:
The mole ratio of N₂ to NH₃ is 1:2. To produce 6 moles of NH₃, you need (6 moles NH₃) * (1 mole N₂ / 2 moles NH₃) = 3 moles of N₂.
Section 2: Mole-to-Gram Conversions
Instructions: Convert moles of a substance to grams, or grams to moles, using molar mass.
Problem 3:
Calculate the mass in grams of 2.5 moles of carbon dioxide (CO₂). The molar mass of CO₂ is 44.01 g/mol.
Answer 3:
Mass (g) = moles * molar mass = 2.5 moles * 44.01 g/mol = 110.025 g
Problem 4:
How many moles are present in 100 grams of sodium chloride (NaCl)? The molar mass of NaCl is 58.44 g/mol.
Answer 4:
Moles = mass (g) / molar mass = 100 g / 58.44 g/mol = 1.71 moles (approximately)
Section 3: Limiting Reactants and Percent Yield
Instructions: Identify the limiting reactant and calculate the theoretical and percent yield.
Problem 5:
Consider the reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂
If 5 moles of Fe₂O₃ react with 10 moles of CO, what is the limiting reactant, and how many moles of iron (Fe) are produced?
Answer 5:
The mole ratio of Fe₂O₃ to CO is 1:3. For every 1 mole of Fe₂O₃, you need 3 moles of CO. With 5 moles of Fe₂O₃, you would need 15 moles of CO. Since you only have 10 moles of CO, CO is the limiting reactant.
Using the mole ratio of CO to Fe (3:2), the number of moles of Fe produced is (10 moles CO) * (2 moles Fe / 3 moles CO) = 6.67 moles of Fe (approximately).
Problem 6:
In a reaction where the theoretical yield of a product is 25 grams, and the actual yield is 18 grams, what is the percent yield?
Answer 6:
Percent yield = (actual yield / theoretical yield) * 100% = (18 g / 25 g) * 100% = 72%
Further Practice and Resources
This worksheet provides a foundational understanding of stoichiometry. To solidify your knowledge, consider working through additional practice problems found in your chemistry textbook or online. Remember to always carefully balance chemical equations before attempting any stoichiometric calculations. Understanding mole ratios and mastering the conversions between moles, grams, and numbers of particles are critical skills for success in chemistry.
