Chemistry Matter and Change: Chapter 11 Stoichiometry – Flashcards
Unlock all answers in this set
Unlock answersquestion
Stoichiometry
answer
study of quantitative relationships between the amounts of reactants used and the amounts of products formed in a chemical reaction
question
Mass of Reactants =
answer
Mass of Products
question
Number of atoms of each element on the reactant side of the equation =
answer
the number of atoms of each element on the product side of the equation
question
Number of moles of each element on the reactant side of the equation =
answer
the number of moles of each element on the product side of the equation
question
Mole Ratio
answer
ratio of the coefficients of any two substances in a balanced chemical equation. Coefficient of Unknown / Coefficient of Known
question
4Al + 3O₂→ 2Al₂O₃
answer
Mole Ratios: 4 moles Al / 3 moles O₂ or 3 moles O₂ / 4 moles Al 4 moles Al / 2 moles 2Al₂O₃ or 2 moles Al₂O₃/ 4 moles Al 3 moles O₂/ 2 moles 2Al₂O₃ or 2 moles Al₂O₃/ 3 moles O₂
question
Mole to Mole Conversion (1 step)
answer
Given the number of moles of a substance (moles of the Known) in a balanced chemical equation, finding the moles needed of another substance (moles of the Unknown) in the equation. Moles of Unknown = Moles of known x Mole Ratio
question
In the equation: 4Al + 3O₂→ 2Al₂O₃, how many moles of Al₂O₃will be produced if there are 3.75 moles of O₂?
answer
3.75 moles O₂ x 2 moles Al₂O₃/ 3 moles O₂ = 2.50 moles Al₂O₃
question
In the equation: C₃H₈ + 5O₂→ 3CO₂+ 4H₂O How many moles of CO₂are produced when 7 moles of C₃H₈ are burned?
answer
7 moles C₃H₈ x 3 moles CO₂ / 1 mole C₃H₈ = 21 moles CO₂
question
Mass to Mass Conversion (3 steps)
answer
Converting from the mass of the Known to the mass of the Unknown. Mass of Known / Molar Mass of Known x Mole Ratio x Molar Mass of Unknown
question
In the equation: NH₄NO₃ → N₂O + 2H₂O How many grams of H₂O are produced if you are given 50 g of NH₄NO₃?
answer
50 g NH₄NO₃/ 80.04 g/mol x 2 moles H₂O / 1 mole NH₄NO₃x 18.02 g/mol H₂O = 22.5 g H₂O
question
Mole to Mass Conversion
answer
Moles Known x Mole Ratio x Molar Mass Unknown
question
In the equation: 2Na + Cl₂→ 2NaCl How many grams of NaCl are produced from 3.75 moles of Cl₂?
answer
3.75 moles Cl₂ x 2moles NaCl/1 mole Cl₂ x 58.5g/mol NaCl = 438.75 g NaCl
question
Mass to Mole Conversion
answer
Mass Known / Molar Mass Known x Mole Ratio
question
In the equation: 2Na + Cl₂→ 2NaCl How many moles of Na are needed if 285 g of NaCl are produced?
answer
285g NaCl / 58.5 g/mol x 2 moles Na / 2 moles NaCl = 4.87 moles Na.
question
How to determine the limiting (and excess) reactants.
answer
Conduct two separate mass-to-mass (or mole-to-mole) stoichiometric calculations; comparing the mass of each reactant to a chosen product.
question
Limiting Reactant:
answer
the reactant that limits the amount of product formed in a chemical reaction. It is the reactant that produces the least amount of the chosen product.
question
Excess Reactant:
answer
the reactant that is present in excess; after the reaction has concluded, a portion of this reactant will be left un - reacted. It will be the reactant that produces the greater amount of the chosen product.
question
Limiting Reactant Problem:
answer
Given the following reaction: S₈ + 4Cl₂ → 4S₂Cl₂. If there is 200g of sulfur and 100g of chlorine, what mass of disulfur dichloride will be produced? (This will be determined by which reactant will produce the least amount of disulfur dichloride).
question
Perform a mass-to-mass calculation between sulfur and disulfur dichloride.
answer
200g S₈ x 1mol S₈ / 256.5g S₈ x 4mol S₂Cl₂ / 1 mol S₈ x 135g S₂Cl₂ / 1 mol S₂Cl₂ = 421g S₂Cl₂.
question
Perform a mass-to-mass calculation between chlorine and disulfur dichloride.
answer
100g Cl₂ x 1mol Cl₂ / 70.91g Cl₂ x 4mol S₂Cl₂ / 4 mol Cl₂ x 135g S₂Cl₂ / 1 mol S₂Cl₂ = 190.4g S₂Cl₂.
question
The limiting reactant is chlorine (Cl₂ ) because...
answer
it produced only 190.4g S₂Cl₂.
question
The excess reactant is sulfur (S₈) because...
answer
it would have produced 421g S₂Cl₂.
question
Determining the amount of excess reactant used and the amount of excess reactant left over in the reaction.
answer
Perform a mass-to-mass stoichiometric calculation between the two reactant, using the limiting reactant (Cl₂) as the known quantity and the excess reactant (S₈) as the unknown quantity.
question
100g Cl₂ x 1mol Cl₂ / 70.91g Cl₂ x 1 mol S₈ / 4mol Cl₂ x 265.5g S₈ = 93.6g S₈
answer
Of the 200g of S₈ that was supplied as a reactant, only 93.6g was needed to react with the 100g of Cl₂ (the limiting reactant).
question
The amount of S₈ in excess is the amount supplied minus the amount used...
answer
200g - 93.6g = 106.4g of S₈ in excess
question
Percent Yield
answer
The ratio of the amount of product that is expected to be produced in a chemical reaction (using stoichiometric calculations based upon the balanced chemical equation) and the amount of product actually produced when carried out in an actual experiment.
question
Theoretical Yield:
answer
the amount of product that is expected to be produced in a chemical reaction (using stoichiometric calculations based upon the balanced chemical equation)
question
Actual Yield:
answer
the amount of product actually produced when an actual experiment is carried out.
question
Percent Yield Equation:
answer
Percent Yield = (Actual Yield ÷ Theoretical Yield) × 100
question
Percent Yield Problem:
answer
Calculate the % Yield of solid silver chromate produced in the following reaction: K₂CrO₄ + 2AgNO₃ → Ag₂CrO₄ + 2KNO₃ In the reaction there was .500g of the limiting reactant AgNO₃. In the actual experiment, .455g of Ag₂CrO₄ was produced.
question
Calculating the Theoretical Yield of Ag₂CrO₄ that was produced.
answer
.500g AgNO₃ x 1 mole AgNO₃ / 169.9g AgNO₃ x 1mole Ag₂CrO₄ / 2 mole AgNO₃ x 331.7 g Ag₂CrO₄ / 1 mol Ag₂CrO₄ = .488g Ag₂CrO₄.
question
Find the ratio of the actual yield (.455g) to the theoretical yield (.488g) ...
answer
% Yield = (.455g Ag₂CrO₄ ÷ .488g Ag₂CrO₄ ) x 100 = 93.2 %
