1. Chapter 5 Chemical Quantities and Reactions
5.6
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 or destroyed
no change in total mass occurs
the mass of products is equal to mass of reactants

3. Conservation of Mass

4. Information from a Balanced Equation

5. Reading Equations in Moles
Consider the following equation:
2Fe(s) S(s) Fe2S3(s)
This equation can be read in “moles” by placing the
word “moles of” between each coefficient and formula.
2 moles of Fe + 3 moles of S mole of Fe2S3

6. Writing Conversion Factors from Equations
A mole–mole factor is a ratio of the moles for any two
substances in an equation.
2Fe(s) + 3S(s) Fe2S3(s)
Fe and S moles Fe and moles S
3 moles S moles Fe
Fe and Fe2S moles Fe and moles Fe2S3
1 mole Fe2S moles Fe
S and Fe2S moles S and mole Fe2S3
1 mole Fe2S moles S

7. Learning Check Consider the following equation: 3H2(g) + N2(g) 2NH3(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

8. Solution 3H2(g) + N2(g) 2NH3(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

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

10. Guide to Using Mole–Mole Factors

11. Learning Check How many moles of Fe are needed for the reaction of
12.0 moles of O2?
4Fe(s) + 3O2(g) Fe2O3(s)
A moles of Fe
B moles of Fe
C moles of Fe

12. Solution In a problem, identify the compounds given and needed.
How many moles of Fe are needed for the reaction of
12.0 moles of O2?
4Fe(s) + 3O2(g) Fe2O3(s)
Step 1 State the given and needed quantities.
Given: moles of O2 Needed: ? moles of Fe
The possible mole factors for the solution are:
4 moles Fe and 3 moles O2
3 moles O2 4 moles Fe

13. Solution
Step 2 Write a plan to convert the given to the needed moles. Mole–mole factor
Moles of O Moles of Fe
Step 3 Use coefficients to write relationships and mole–mole factors.
4 moles of Fe = moles of O2
4 moles Fe and 3 moles O2
3 moles O moles Fe

14. Solution
Step 4 Set up the problem using the mole–mole factor that cancels given moles.
12.0 moles O2 x 4 moles Fe = moles of Fe
3 moles O2
The answer is C, 16.0 moles of Fe.