Stoichiometry

Stoichiometry

Introduction to Stoichiometry

• Reaction stoichiometry: Deals with mass relationships between reactants and products.

• Composition stoichiometry: Deals with mass relationships of elements in compounds.

• All reaction stoichiometry calculations start with a balanced chemical equation.

• Mole ratio: Conversion factor that relates the amounts in moles of any two substances in a chemical reaction.

• Reaction stoichiometry uses molar relationships to determine unknown amounts of reactants or products from known amounts.

Problem Types

• Type 1: Given and unknown are amounts in moles: amount of given substance (mol) → amount of unknown substance (mol).

• Type 2: Given is amount in moles, unknown is mass: amount of given substance (mol) → amount of unknown substance (mol) → mass of unknown substance (g).

• Type 3: Given is mass, unknown is amount in moles: mass of given substance (g) → amount of given substance (mol) → amount of unknown substance (mol).

• Type 4: Given and unknown are masses: mass of given substance (g) → amount of given substance (mol) → amount of unknown substance (mol) → mass of unknown substance (g).

Mole Ratio

• Mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction.

• Obtained directly from the balanced chemical equation.

• Example: $2Al<em>2O</em>3(l) \rightarrow 4Al(s) + 3O_2(g)$

  • Mole ratios:

    • $\frac{2 \text{ mol } Al<em>2O</em>3}{4 \text{ mol } Al}$ or $\frac{4 \text{ mol } Al}{2 \text{ mol } Al<em>2O</em>3}$

    • $\frac{2 \text{ mol } Al<em>2O</em>3}{3 \text{ mol } O<em>2}$ or $\frac{3 \text{ mol } O</em>2}{2 \text{ mol } Al<em>2O</em>3}$

    • $\frac{4 \text{ mol } Al}{3 \text{ mol } O<em>2}$ or $\frac{3 \text{ mol } O</em>2}{4 \text{ mol } Al}$

• Molar mass: mass in grams of one mole of a substance.

• Example:

  • $1 \text{ mol } Al<em>2O</em>3 = 101.96 \text{ g}$

  • $1 \text{ mol } Al = 26.98 \text{ g}$

  • $1 \text{ mol } O_2 = 32.00 \text{ g}$

Ideal Stoichiometric Calculations

• Balanced chemical equation provides amounts of reactants and products under ideal conditions.

• Solving any reaction stoichiometry problem must begin with a balanced equation.

Mole-to-Mole Conversions

• General plan: amount of given substance (mol) → amount of unknown substance (mol).

• Requires the stoichiometric mole ratio of the unknown to given substance from balanced equation.

• given quantity × conversion factor = unknown quantity.

Mole-to-Gram Calculations

• General plan: amount of given substance (mol) → amount of unknown substance (mol) → mass of unknown substance (g).

• Requires mole ratio of unknown substance to given substance and molar mass of unknown substance.

Gram-to-Mole Conversions

• General plan: mass of given substance (g) → amount of given substance (mol) → amount of unknown substance (mol).

• Requires molar mass of the given substance and the mole ratio.

Mass-to-Mass Conversions

• General plan: mass of given substance (g) → amount of given substance (mol) → amount of unknown substance (mol) → mass of unknown substance (g).

• Requires molar mass of given substance, mole ratio, and molar mass of unknown substance.

Limiting Reactants and Percentage Yield

• Limiting reactant: Substance completely used up first in a reaction; limits the amount of other reactant and product that can form.

• Excess reactant: Substance not used up completely in a reaction.

Percentage Yield

• Theoretical yield: Maximum amount of product that can be produced.

• Actual yield: Measured amount of product obtained from a reaction.

• Percentage yield: $\frac{\text{actual yield}}{\text{theoretical yield}} × 100$

• Comparing actual and theoretical yields helps chemists determine reaction efficiency.

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant

The limiting reactant is the substance that is completely used up first in a chemical reaction. It determines the maximum amount of product that can be formed. To find the limiting reactant, you need to compare the mole ratios of the reactants to the stoichiometric ratios from the balanced chemical equation. The reactant