Chemistry: Mole Ratios and Molecular Equations

Mole Ratios

• A mole ratio is a ratio of the amount of one substance to the amount of another substance in a reaction.
• It is used to relate the amount of reactants and products in a chemical reaction.
• Mole ratios are derived from the coefficients of a balanced chemical equation.
• The mole ratio of reactants to products can be used to determine the amount of product formed or the amount of reactant required.

Molecular Equations

• A molecular equation is a chemical equation that shows the reactants and products as molecules.
• It does not show the ionic species present in the reaction.
• Molecular equations are not balanced in terms of ions, but rather in terms of molecules.
• Molecular equations are often used to represent reactions that occur in non-aqueous solutions or in the gas phase.

Stoichiometric Calculations

Amount of Product Formed

• The amount of product formed can be calculated using the mole ratio and the amount of reactant.
• The formula is: amount of product = mole ratio x amount of reactant
• Units: moles, grams, or volume (for gases)

Amount of Reactant Required

• The amount of reactant required can be calculated using the mole ratio and the amount of product.
• The formula is: amount of reactant = mole ratio x amount of product
• Units: moles, grams, or volume (for gases)

Limiting Reagent

• The limiting reagent is the reactant that is consumed completely in a reaction.
• It determines the amount of product formed.
• The limiting reagent can be identified by calculating the amount of product formed from each reactant and determining which reactant produces the least amount of product.

Percent Yield

• The percent yield is the ratio of the actual amount of product formed to the theoretical amount of product.
• The formula is: percent yield = (actual amount of product / theoretical amount of product) x 100
• Units: percentage

Mole Ratios

• A ratio of the amount of one substance to the amount of another substance in a reaction, used to relate reactants and products.
• Derived from coefficients of a balanced chemical equation.
• Used to determine amount of product formed or amount of reactant required.

Molecular Equations

• A chemical equation showing reactants and products as molecules.
• Does not show ionic species present in the reaction.
• Balanced in terms of molecules, not ions.
• Often used to represent reactions in non-aqueous solutions or gas phase.

Stoichiometric Calculations

Amount of Product Formed

• Calculated using mole ratio and amount of reactant: amount of product = mole ratio x amount of reactant.
• Units: moles, grams, or volume (for gases).

Amount of Reactant Required

• Calculated using mole ratio and amount of product: amount of reactant = mole ratio x amount of product.
• Units: moles, grams, or volume (for gases).

Limiting Reagent

• The reactant consumed completely in a reaction, determining amount of product formed.
• Identified by calculating amount of product formed from each reactant and finding the reactant producing the least amount of product.

Percent Yield

• The ratio of actual amount of product formed to theoretical amount of product: percent yield = (actual amount of product / theoretical amount of product) x 100.
• Units: percentage.

Stoichiometric Calculations

• Involve the use of balanced chemical equations to determine the amount of reactants required or products formed in a chemical reaction.

Types of Stoichiometric Calculations

• Mole-to-Mole Calculations: relate the number of moles of one substance to the number of moles of another substance.
• Mole-to-Mass Calculations: relate the number of moles of a substance to its mass.
• Mass-to-Mass Calculations: relate the mass of one substance to the mass of another substance.

Steps for Stoichiometric Calculations

• Write and Balance the Equation: ensure that the number of atoms of each element is equal on both the reactant and product sides.
• Identify the Known and Unknown Quantities: identify the known quantities (e.g. amount of reactant) and the unknown quantities (e.g. amount of product).
• Choose a Conversion Factor: choose a conversion factor (e.g. mole ratio, molar mass) to relate the known and unknown quantities.
• Perform the Calculation: use the chosen conversion factor to perform the calculation.
• Check the Units: ensure that the units of the answer are correct.

Stoichiometric Calculation Examples

Mole-to-Mole Calculation

• Calculate the number of moles of oxygen required to react with 2 moles of hydrogen to form water.
• Use the conversion factor: 2H2 + O2 → 2H2O (2:1 mole ratio).
• Calculate: 2 moles H2 × (1 mole O2 / 2 moles H2) = 1 mole O2.

Mole-to-Mass Calculation

• Calculate the mass of carbon dioxide produced when 1 mole of calcium carbonate is heated.
• Use the conversion factor: CaCO3 → CaO + CO2 (1:1 mole ratio, molar mass of CO2 = 44 g/mol).
• Calculate: 1 mole CaCO3 × (1 mole CO2 / 1 mole CaCO3) × 44 g/mol = 44 g CO2.