Questions and Answers
What is stoichiometry?
Study of quantitative relationships between the amounts of reactants used and the amounts of products formed in a chemical reaction.
Mass of Reactants = _____
Mass of Products
Number of atoms of each element on the reactant side of the equation = _____
the number of atoms of each element on the product side of the equation
Number of moles of each element on the reactant side of the equation = _____
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What is a mole ratio?
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In the equation 4Al + 3O₂→ 2Al₂O₃, the mole ratios can be calculated between Al and O₂.
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How do you perform a mole to mole conversion using the mole ratio?
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How many moles of Al₂O₃ will be produced if there are 3.75 moles of O₂ in the equation 4Al + 3O₂→ 2Al₂O₃?
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How many moles of CO₂ are produced when 7 moles of C₃H₈ are burned in the reaction C₃H₈ + 5O₂→ 3CO₂ + 4H₂O?
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What is the formula for mass to mass conversion?
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How many grams of H₂O are produced if you are given 50 g of NH₄NO₃ in the reaction NH₄NO₃ → N₂O + 2H₂O?
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How do you calculate the theoretical yield of a substance?
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What is the percent yield equation?
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What defines a limiting reactant?
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What is meant by excess reactant?
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How much of the excess reactant (S₈) was left after the reaction with Cl₂?
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Study Notes
Stoichiometry Overview
- The study of quantitative relationships in chemical reactions, involving reactants and products.
Mass Relationships
- Mass of reactants equals mass of products in a reaction.
Conservation of Atoms
- The number of atoms for each element must be equal on both sides of the reaction equation.
Molar Relationships
- The number of moles for each element must also be equal on both sides of the equation.
Mole Ratio
- Derived from the coefficients of balanced chemical equations, used for conversions.
Example of Mole Ratios
- For the equation 4Al + 3O₂ → 2Al₂O₃, various mole ratios can be established:
- 4 moles Al : 3 moles O₂
- 3 moles O₂ : 2 moles Al₂O₃
Mole to Mole Conversion
- Determine moles of an unknown substance using the formula: Moles of Unknown = Moles of Known x Mole Ratio.
Example Problem: O₂ to Al₂O₃ Conversion
- From the equation, if 3.75 moles O₂ are given, 2.50 moles Al₂O₃ are produced.
Example Problem: C₃H₈ to CO₂ Conversion
- Burning 7 moles of C₃H₈ produces 21 moles of CO₂.
Mass to Mass Conversion
- To convert from mass of the Known to the mass of the Unknown, follow: Mass of Known / Molar Mass of Known x Mole Ratio x Molar Mass of Unknown.
Example Problem: NH₄NO₃ to H₂O
- From 50 g of NH₄NO₃, 22.5 g of H₂O are produced.
Mole to Mass Conversion
- Calculated using: Moles Known x Mole Ratio x Molar Mass of Unknown.
Mass to Mole Conversion
- Achieved through: Mass Known / Molar Mass Known x Mole Ratio.
Limiting and Excess Reactants
- Limiting reactant is the one that produces the least amount of product.
- Excess reactant remains un-reacted after the reaction.
Limiting Reactant Problem Example
- In the reaction S₈ + 4Cl₂ → 4S₂Cl₂ with 200 g S₈ and 100 g Cl₂:
- Perform separate calculations to determine S₂Cl₂ production from each reactant.
Mass-to-Mass Calculation Example
- For sulfur, 421 g of S₂Cl₂ can be produced.
- For chlorine, only 190.4 g of S₂Cl₂ can be produced, making Cl₂ the limiting reactant.
Excess Reactant Calculation
- Remaining S₈ after reaction:
- 200 g S₈ supplied, 93.6 g used, leaving 106.4 g in excess.
Percent Yield
- Ratio of actual amount produced to the expected (theoretical) amount, expressed as a percentage.
Theoretical Yield
- Expected production based on stoichiometric calculations.
Actual Yield
- The amount of product produced during an experiment.
Percent Yield Equation
- Percent Yield = (Actual Yield ÷ Theoretical Yield) × 100.
Percent Yield Example Problem: Ag₂CrO₄
- Calculating yield from reaction K₂CrO₄ + 2AgNO₃ → Ag₂CrO₄ involves finding theoretical yield from limiting reactant AgNO₃ first.
- Given 0.500 g of AgNO₃, the theoretical yield calculated is 0.488 g.
- Actual yield of Ag₂CrO₄ is 0.455 g, leading to a percent yield of 93.2%.
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Description
Test your knowledge of stoichiometry with these flashcards covering key concepts and definitions. Understand the quantitative relationships in chemical reactions and the relationship between reactants and products. Perfect for mastering Chapter 11 content in chemistry.
