1. Calculations with Equations
CHAPTER 9
Mole Ratios
Calculations with Equations

2. Mole-Mole Factor
Shows the mole-to-mole ratio between two of the substances in a balanced equation
Derived from the coefficients of any two substances in the equation

3. Writing Mole Factors – identifies the mole-ratio existing between the substances involved in a given chemical equation
4 Fe O Fe2O3
Fe and O2
4 mol Fe and 3 mol O2
3 mol O mol Fe
Fe and Fe2O3
4 mol Fe and 2 mol Fe2O3
2 mol Fe2O3 4 mol Fe

4. 4 Fe + 3 O2 2 Fe2O3 MOLE RATIO of O2 and Fe2O3
3 mol O2 and 2 mol Fe2O3
2 mol Fe2O mol O2

5. Review examples 3 H2(g) + N2(g) 2 NH3(g)
A. A mol factor for H2 and N2 is
1) 3 mol N ) 1 mol N ) 1 mol N2
1 mol H mol H mol H2
B. A mol factor for NH3 and H2 is
1) 1 mol H ) 2 mol NH ) 3 mol N2
2 mol NH mol H mol NH3

6. Chemical Calculations
4 Fe O Fe2O3
How many moles of Fe2O3 are produced when 6.0 moles O2 react?
6.0 mol O2 x mol Fe2O3 = 4.0 mol Fe2O3
mol O2 2 3

7. How many moles of Fe are needed to react with 12.0 mol of O2?
4 Fe O Fe2O3
12.0 mol O2 x mol Fe = mol Fe
mol O2 4 3

8. 4 Fe + 3 O2 2 Fe2O3. How many grams of O2 are needed to produce 0
4 Fe O Fe2O3 How many grams of O2 are needed to produce mol of Fe2O3?
0.400 mol Fe2O3 x 3 mol O x g O2
2 mol Fe2O mol O2
= g O2

9. Calculating Mass of A Substance in a Stoichiometric Equation
Balance equation
Convert starting amount to moles
Use coefficients to write a mol-mol factor
Convert moles of desired to grams

10. Calculation
The reaction between H2 and O2 produces 13.1 g of water. How many grams of O2 reacted?
Write the equation
H2 (g) O2 (g) H2O (g)
Balance the equation
2 H2 (g) O2 (g) 2 H2O (g)

11. Organize data mol bridge 2 H2 (g) + O2 (g) 2 H2O (g) ? g 13.1 g
Plan g H2O mol H2O mol O g O2
Setup
13.1 g H2O x 1 mol H2O x 1 mol O2 x g O g H2O 2 mol H2O 1 mol O2
= g O2

12. How many O2 molecules will react with 505 grams of Na to form Na2O?
4 Na O Na2O
505 g Na x 1 mol Na x 1 mol O2 x 6.02 x 1023
23.0 g Na mol Na 1 mol O2
= x 1024 molecules

13. Acetylene gas C2H2 burns in the oxyactylene torch for welding
Acetylene gas C2H2 burns in the oxyactylene torch for welding. How many grams of C2H2 are burned if the reaction produces 75.0 g of CO2?
2 C2H O CO H2O
75.0 g CO2 x 1 mol CO2 x 2 mol C2H2 x 26.0 g C2H2
44.0 g CO mol CO mol C2H2
= g C2H2