Questions and Answers
What is stoichiometry?
The calculation of quantities in chemical reactions is a subject of chemistry.
What is a mole ratio?
A conversion factor derived from coefficients of a balanced chemical equation interpreted in terms of moles.
What is a limiting reagent?
The reagent that determines the amount of product that can be formed by a reaction.
What is an excess reagent?
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What is theoretical yield?
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What is actual yield?
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What is percent yield?
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How do chemists use balanced chemical equations?
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What quantities can you interpret from a balanced chemical equation?
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In a chemical reaction, mass is conserved.
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In mole to mole conversions: Amount of given substance A in moles multiplied by mole ratio from balanced equation equals amount of unknown substance B in moles. A (in moles) x ____ = B (in moles)
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In mole to mass conversions: Amount of given substance A in moles multiplied by #1: Mole ratio from balanced equation multiplied by #2 Molar Mass from periodic table equals amount of unknown substance B in grams. A (in moles) x #1 x #2 = B (in grams)
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In mass to mole conversions: Amount of given substance A in grams multiplied by #2 Molar mass from periodic table multiplied by #1 Mole ratio from balanced equation equals amount of unknown substance B in moles. A (in grams) x #2 x #1 = B (in moles)
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In mass to mass conversions: Amount of given substance A in grams multiplied by #2 Molar mass from periodic table multiplied by #1 Mole ratio from balanced equation multiplied by #3 Molar mass from periodic table equals amount of unknown substance B in grams. A (in grams) x #2 x #1 x #3 = B (in grams)
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How do you convert grams of substance A to molecules of substance B?
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Given the reaction N₂ + 3F₂ → 2NF₃, how many molecules of nitrogen are needed to produce 3.17g of nitrogen trifluoride?
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Given the reaction N₂(g) + 3H₂(g) → 2NH₃ (g), if 14.5 liters of hydrogen gas is used, how many liters of ammonia would be produced?
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Identify the limiting and excess reactants in the reaction Mg + 2H₂O → Mg(OH)₂ + H₂ when 16.2 g Mg are reacted with 12.0g H₂O.
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What does the percent yield of a reaction measure?
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Calculate the percent yield given that the actual yield is 46.3 g KCl and the theoretical yield is 49.4 g KCl.
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Study Notes
Stoichiometry Basics
- Stoichiometry involves calculating quantities in chemical reactions.
- A mole ratio is derived from the coefficients in a balanced chemical equation, used as a conversion factor.
Key Concepts
- The limiting reagent is the reactant that limits the amount of product formed in a reaction.
- An excess reagent is the reactant that remains unreacted after the reaction completes.
- The theoretical yield represents the maximum possible product yield from given reactants, while actual yield is the product amount obtained in practice.
- Percent yield is the ratio of actual yield to theoretical yield, expressed as a percentage.
Application of Balanced Equations
- Chemists utilize balanced chemical equations for determining reactant quantities needed and product amounts generated.
- A balanced equation provides insight into numbers of atoms, molecules, or moles along with their mass and volume conversions.
Conservation of Mass Principle
- In chemical reactions, mass conservation means that matter cannot be created or destroyed.
Conversion Processes
- Mole to Mole: Use mole ratios to convert amount of one substance in moles to another.
- Mole to Mass: Multiply moles by mole ratio and then by the molar mass to find mass in grams.
- Mass to Mole: Use grams multiplied by molar mass and mole ratio to determine moles.
- Mass to Mass: Combine grams, mole ratios, and molar masses to convert between masses of two substances.
- Mass to Molecules: Convert grams to molecules or vice versa.
Examples
- Mass to Molecules Conversion: To find the number of molecules of nitrogen needed for 3.17g of nitrogen trifluoride, the result is 1.33 x 10²² molecules of N₂.
- Volume to Volume Conversion Example: From 14.5 L of hydrogen gas, 9.67 L of ammonia can be produced under STP conditions.
Limiting Reactants Example
- Given the reaction Mg + 2H₂O → Mg(OH)₂ + H₂, with 16.2g of Mg and 12.0g of H₂O:
- Limiting reagent: 12.0g H₂O
- Excess reagent: 16.2g Mg
Percent Yield Calculation
- Percent yield measures a reaction's efficiency:
- Given actual yield of 46.3g KCl and theoretical yield of 49.4g KCl, the calculation is:
- % yield = (46.3g / 49.4g) x 100.
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