1. Homework 7 due today
I’m ready for a break

2. 2C2H6 + 7O2 4CO2 + 6H2O 30 32 44 18 g/mol Answer: 2 grams of CO2
Solving Stoichiometry Problems (Moles level 3) : Two approaches reviewed with an example:
Factor –label method
Mole-ratio method
2C2H6 + 7O2 4CO2 + 6H2O
g/mol
g of C2H6 burns to make how many
grams of CO2?
Answer: 2 grams of CO2

3. Practicing…clickers and not clickers

4. 3 mol H2O C3H8 + 5O2-------- 3CO2 + 4H2O 44 32 44 18 g/mol
weight to moles
How many moles of H2O form if 33 g of C3H8 are burned ?
3 mol H2O

5. How many moles of CO2 form if we burn 1.4667 g C3H8 ? (weight mol)
C3H8 + 5O  3CO2 + 4H2O
g/mol
How many moles of CO2 form if we burn g C3H8 ? (weight mol)
0.033
0.100
0.133
0.166

6. =4*1022 How many molecules of CO2 form along with 1.592 g H2O ?
C3H8 + 5O  3CO2 + 4H2O
g/mol
f) weight to count
How many molecules of CO2 form along with g H2O ?
=4*1022

7. C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM)
g/mol
How many molecules of O2 are needed to burn g C3H8? (1 mol count =6*1023) (wtcount)
2*1022
4*1021
1.76*1023

8. 3*1022 CO2 molecules C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM)
g/mol
molcount
How many molecules of CO2 form along with mol of H2O ? (1 mol count=6*1023)
3*1022 CO2 molecules

9. C3H8 + 5O2-------- 3CO2 + 4H2O (BOOM)
g/mol
Mol count: How many molecules of O2 does it take to form moles of CO2 in the reaction above? (1 mol count=6*1023)
1.2*1022
7.2*1021
1.0*1022
2.0*1022

10. Need more practice ?????

11. The mole road trip itinerary so far now:
% composition problems and combustion analysis (pp )
Reaction balancing (pp )
Reaction stoichiometry predictions, limiting yields and % yields ( pp )

12. Limiting yield and % yield calculations are the last stop on the mole bus trip

13. What’s the maximum distance you can expect to travel ??
A non-chemical example of a `limiting’ yield problem
You have gotten lost on the Ad Dahna desert –largest desert on the Saudi peninisula. To avoid perishing you must reach the nearest oasis which is 100 km away. You can walk at maximum 10 km/ day. You need to consume at least 2 liters of water and ½ kg of food per day to walk that distance.
You have in your pack:
16 liters of water
5 kg of food
Broken cell phone
What’s the maximum distance you can expect to travel ??

14. Food Calculation 5 kg food = 10 days ½ kg/day day
=>10 days * 10 km = 100 km 
day

15. The winner is….always the smaller one…
Water Calculation
16 liters = 8 days
2 liters/day
8 days * 10 km = 80 km  day
The winner is….always the smaller one…
it limits.

16. 3 examples of limiting yield calculations via the `cut and try’ approach (on board)
example #1:mol-mol
5O2 + C3H8  3CO2 + 4H2O
mol ?? mol
Given 0.33 mol O2 and 0.10 mol C3H8, compute the maximum theoretical yield of CO2 moles
Ans. 0.2 mol CO2
(O2 limits)

17. How many mol of H2O form from burning 0.125 mol C3H8 with 0.7 mol O2 ?
5O2 + C3H8  3CO2 + 4H2O
Mol mol ?
How many mol of H2O form from burning mol C3H8 with 0.7 mol O2 ?
0.56 mol
0.50 mol
0.42 mol
0.375 mol

18. The `cut & try’ approach to limiting yield calculations (cont.)
0.18 g H2O
(O2 limits)
example #2: wt-wt
5O2 + C3H8  3CO2 + 4H2O
g ? g MW
Given 4.0 grams O2 and 2.2 grams C3H8, compute the theoretical yield of H2O in grams for the combustion shown above.

19. Given 3.24 g C8H18 and 1.136 g O2, how many grams of CO2 form ?
2C8H O  16CO H2O
MW g/mol g/mol g/mol 18 g/mol
w(g) ?? g
Given 3.24 g C8H18 and g O2, how many grams of CO2 form ?
10.0 g
1.0 g
0.11 g
1.56 g

20. Cut and try approach example #3: mixed  grams
C12H22O O  12CO H2O
MW g/mol g/mol g/mol 18 g/mol
w(g) ?? g
How many grams of CO2 will be produced if 1.2*1023 molecules of sucrose, C12H22O11, are combined with grams of O2 according to the balanced equation above?
100 g CO2
(O2 limits)

21. 2C8H O  16CO H2O
MW g/mol g/mol g/mol 18 g/mol
w(g) ?? g
Given 1.705*1022 molecules of C8H18 and g O2, how many grams of CO2 form ?
10.0 g
1.0 g
0.11 g
1.56 g