7.1 & 7.2 Mole Ratios & Mass Relationships pp. 316 - 324

Mole Ratios in Balanced Chemical Equations A balanced equation tells us the ratio of the amounts of reactants and products taking part in a chemical reaction N2(g) + 3H2(g) → 2NH3(g) 1 molecule 3 molecules 2 molecules 1 dozen molecules 3 dozen molecules 2 dozen molecules 1 mol nitrogen 3 mol hydrogen 2 mol ammonia The ratio of reacting amounts is called the mole ratio 1 : 3 : 2 in this case

Calculating Masses of Reactants and Products Whether we are baking cookies in the kitchen or manufacturing fertilizers in a factory, we need to be able to calculate the quantity of reactants needed to produce a certain quantity of product To predict masses of reactants and products, we always begin with a balanced equation for the reaction Then we use the mole ratios given by the coefficients in the equation and convert the relationships to masses as needed

Gravimetric Stoichiometry The procedure for calculating the masses of reactants or products in a chemical reaction is called gravimetric stoichiometry gravimetric refers to mass measurements stoichiometry refers to the relationship between the quantities of reactants and products involved in chemical reactions

Summary: Calculating Masses of Reactants and Products Begin with a balanced chemical equation, with the measured mass of reactant or product written beneath the corresponding formula. 1. Convert the measured mass into an amount in moles. 2. Use the mole ratio in the balanced equation to predict the amount in moles of desired substance. 3. Convert the predicted amount in moles into mass.

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) Sample Problem Iron is the most widely used metal in North America. It may be produced by the reaction of iron(III) oxide, from iron ore, with carbon monoxide to produce iron metal and carbon dioxide. What mass of iron(III) oxide is required to produce 100.0 g of iron? First we need a balanced chemical equation: Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) How many moles of iron is 100.0g of iron? n = m ÷ M = 100.0 g ÷ 55.85 g/mol = 1.790 mol

What is the mole relationship between iron(III)oxide and iron? Fe2O3 : Fe = 1 : 2 Therefore, Now we can convert the moles of iron(III)oxide into grams (the mass required to produce 100.0 g of iron) m = n × M = 0.8952 mol × 159.70 g/mol = 143.0 g

Homework Read pp. 316 - 324 Answer p. 320 # 1 - 9