1. Chemical Reactions and Quantities
5.7
Mole Relationships in
Chemical Equations

2. Law of Conservation of Mass
The Law of Conservation of Mass indicates that in an
ordinary chemical reaction,
Matter cannot be created nor destroyed.
No change in total mass occurs in a reaction.
Mass of products is equal to mass of reactants.

3. Conservation of Mass 2 moles Ag + 1 moles S = 1 mole Ag2S
2 (107.9 g) (32.1 g) = (247.9 g)
247.9 g reactants = g product

4. Reading Equations In Moles
Consider the following equation:
4 Fe(s) O2(g) Fe2O3(s)
This equation can be read in “moles” by placing the
word “moles” between each coefficient and formula.
4 moles Fe moles O moles Fe2O3

5. Writing Mole-Mole Factors
A mole-mole factor is a ratio of the moles for any two
substances in an equation.
4Fe(s) O2(g) Fe2O3(s)
Fe and O moles Fe and 3 moles O2
3 moles O moles Fe
Fe and Fe2O moles Fe and 2 moles Fe2O3
2 moles Fe2O3 4 moles Fe
O2 and Fe2O3 3 moles O and 2 moles Fe2O3
2 moles Fe2O3 3 moles O2

6. Learning Check Consider the following equation:
3 H2(g) N2(g) NH3(g)
A. A mole-mole factor for H2 and N2 is
1) 3 moles N ) 1 mole N ) 1 mole N2
1 mole H moles H moles H2
B. A mole-mole factor for NH3 and H2 is
1) 1 mole H ) 2 moles NH ) 3 moles N2
2 moles NH moles H moles NH3

7. Solution A. A mole-mole factor for H2 and N2 is 2) 1 mole N2
3H2(g) N2(g) NH3(g)
A. A mole-mole factor for H2 and N2 is
2) 1 mole N2
3 moles H2
B. A mole-mole factor for NH3 and H2 is
2) 2 moles NH3

8. Calculations with Mole Factors
How many moles of Fe2O3 can form from 6.0 mole O2?
4Fe(s) O2(g) Fe2O3(s)
Relationship: 3 mole O2 = 2 mole Fe2O3
Write a mole-mole factor to determine the moles of Fe2O3.
6.0 mole O2 x 2 mole Fe2O3 = 4.0 mole Fe2O3
3 mole O2

9. Guide to Using Mole Factors

10. Learning Check
How many moles of Fe are needed for the reaction of moles O2?
4 Fe(s) O2(g) Fe2O3(s)
1) moles Fe
2) moles Fe
3) moles Fe

11. Solution 12.0 moles O2 x 4 moles Fe = 16.0 moles Fe 3 moles O2