1. Chapter 9 Chemical Quantities in Reactions
9.2 Mass Calculations for Reactions
Learning Goal Given the mass in grams of a substance in a reaction, calculate the mass in grams of another substance in the reaction
© 2014 Pearson Education, Inc.

2. Chemical Calculations, Mass to Mass
To convert the mass of substance (A) to mass of a second substance (B) in the reaction, we need
the molar mass of substance A
the mole−mole factors for substance A and B
the molar mass of substance B
Molar Mass A
Mole–Mole factor, B/A
Molar Mass B
grams
of A
moles
of A
moles
of B
grams
of B
© 2014 Pearson Education, Inc.

3. Mass of Product from Mass of Reactant
When acetylene burns in oxygen, high temperatures are produced that can be used in welding metals.
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
How many grams of CO2
can be produced when
54.6 g of C2H2 are burned?

4. Step 1 State the given and needed quantities (grams).
Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
Step 1 State the given and needed quantities (grams).
Given: g of C2H2
Need: grams of CO2

5. Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
54.6 g ? grams Step 2 Write a plan to convert the given to the needed quantity (grams).
grams of
C2H2
Molar Mass
moles of
C2H2
Mole–Mole factor
moles of
CO2
Molar Mass
grams of
CO2

6. Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g) 54.6 g ? grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors. 1 mole of C2H2 = g of C2H2

7. Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g) 54.6 g ? grams Step 3 Use coefficients to write mole−mole factors; write molar mass factors.
1 mole of CO2 = g of CO2

8. Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
54.6 g ? grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors.
2 moles of C2H2 = 4 moles of CO2

9. Mass of Product from Mass of Reactant
How many grams of CO2 can be produced when 54.6 g of C2H2 is burned?
2C2H2(g) + 5O2(g)  4CO2(g) + 2H2O(g)
54.6 g ? grams
Step 4 Set up the problem to give the
needed quantity (grams).

10. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
Step 1 State the given and needed quantities (grams).
Given: g of H2
Need: grams of N2

11. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
?g grams
Step 2 Write a plan to convert the given to the needed quantity (grams).
Molar Mass
Mole–Mole factor
Molar Mass
grams
of H2
moles
of H2
moles
of N2
grams
of N2

12. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
?g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors. 1 mole of H2 = 2.02 g of H2

13. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
?g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors mole of N2 = g of N2

14. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
?g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors mole of N2 = 3 moles of H2

15. Mass of Reactant from Mass of Reactant
How many grams of N2 gas are needed to react with 11.0 g of hydrogen gas to make ammonia, NH3?
N2(g) + 3H2(g)  2NH3(g)
?g grams
Step 4 Set up the problem to give the
needed quantity (grams).

16. Learning Check
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)

17. Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
Step 1 State the given and needed quantities (grams).
Given: g of KCl
Need: grams of K

18. How many grams of potassium are required to produce 36.0 g of KCl?
Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
? g grams
Step 2 Write a plan to convert the given to the needed quantity (grams).
grams of
KCl
moles of
KCl
moles of K
grams of K
Molar Mass
Mole–Mole factor
Molar Mass

19. How many grams of potassium are required to produce 36.0 g of KCl?
Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
? g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors mole of KCl = g of KCl

20. How many grams of potassium are required to produce 36.0 g of KCl?
Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
? g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors moles of KCl = 2 moles of K

21. How many grams of potassium are required to produce 36.0 g of KCl?
Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
? g grams
Step 3 Use coefficients to write mole−mole factors; write molar mass factors. 1 mole of K = g of K

22. Solution
How many grams of potassium are required to produce 36.0 g of KCl?
2K(s) + Cl2(g)  2KCl(s)
? g grams
Step 4 Set up the problem to give the
needed quantity (grams).