1. 7.1 & 7.2 Mole Ratios & Mass Relationshipspp

2. 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) H2(g) → NH3(g)
1 molecule molecules molecules
1 dozen molecules 3 dozen molecules 2 dozen molecules
1 mol nitrogen mol hydrogen mol ammonia
The ratio of reacting amounts is called the mole ratio
1 : 3 : 2 in this case

3. 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

4. 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

5. 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.

7. 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 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 = g ÷ g/mol = mol

8. 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 g of iron)
m = n × M = mol × g/mol = g

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