1. Agenda 1/9/16 1. Quick review 2. Stoichiometry Notes
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Agenda 1/9/16 1. Quick review 2. Stoichiometry Notes

2. Stoichiometric Calculations
Stoichiometry
Stoichiometric Calculations

3. A. Proportional Relationships
2 1/4 c. flour
1 tsp. baking soda
1 tsp. salt
1 c. butter
3/4 c. sugar
3/4 c. brown sugar
1 tsp vanilla extract
2 eggs
2 c. chocolate chips
Makes 5 dozen cookies.
I have 5 eggs. How many cookies can I make?
Ratio of eggs to cookies
5 eggs
5 doz.
2 eggs
= 12.5 dozen cookies

4. A. Proportional Relationships
Stoichiometry
relationships between substances in a chemical reaction
based on the mole ratio
Mole Ratio
indicated by coefficients in a balanced equation
2 Mg + O2  2 MgO

5. What can we do with Stoichiometry?
For the generic equation:
RA +RB → P1 + P2
Given the…
…one can find the…
Amount of one reactant
Amount of other reactant that is needed to react with it
Amount of reactant
Amount of product that will be produced
Amount of product you need to produce
Amount of reactant you must use

6. B. Stoichiometry Steps 1. Write a balanced equation.
2. Identify the given and find.
3. Line up conversion factors.
Mole ratio - moles  moles
Convert amount of Substance A into moles (if needed)
Use a Mole ratio (must be included in ALL stoichiometry problems)
Convert moles of Substance B into desired unit
4. Check answer.

7. Given the equation… 2TiO2 + 4Cl2 + 3C → 2TiCl4 + CO2 + 2CO
How many mol chlorine will react with 4.55 mol carbon?
Given: 4.55 mole C
Find: mole Cl2
6.07 mol Cl2

8. Given the same equation…
2TiO2 + 4Cl2 + 3C → 2TiCl4 + CO2 + 2CO
What mass titanium (IV) oxide will react with 4.55 mol carbon?
given = 4.55 mol C
find = mass of TiO2
g TiO2

9. D. Stoichiometry Problems
How many moles of KClO3 must decompose in order to produce 9 moles of oxygen gas?
2KClO3  2KCl + 3O2
? mol
9 mol
9 mol O2
2 mol KClO3
3 mol O2
= 6 mol
KClO3

10. D. Stoichiometry Problems
How many grams of KClO3 are req’d to produce 9.00 L of O2 at STP?
2KClO3  2KCl + 3O2
? g
9.00 L
9.00 L O2
1 mol O2
22.4 L
2 mol
KClO3
3 mol O2
122.55
g KClO3
1 mol
KClO3
= 32.8 g
KClO3

11. D. Stoichiometry Problems
How many grams of silver will be formed from 12.0 g copper?
Cu + 2AgNO3  2Ag + Cu(NO3)2
12.0 g
? g
12.0
g Cu
1 mol Cu
63.55
g Cu
2 mol Ag
1 mol Cu
107.87
g Ag
1 mol Ag
= 40.7 g Ag

12. D. Stoichiometry Problems
How many grams of Cu are required to react with 1.5 L of 0.10M AgNO3?
Cu + 2AgNO3  2Ag + Cu(NO3)2
? g
1.5L
0.10M
1.5 L
.10 mol
AgNO3
1 L
1 mol Cu
2 mol
AgNO3
63.55
g Cu
1 mol Cu
= 4.8 g Cu

13. The Limiting Reactant
A balanced equation for making a Big Mac® might be:
3 B M + EE  B3M2EE
With…
…and…
…one can make…
30 M
excess B and excess EE
15 B3M2EE
30 B
excess M and excess EE
10 B3M2EE
30 B and excess EE

14. A balanced equation for making a tricycle might be:
3 W P + S + H + F  W3P2SHF
With…
…and…
…one can make…
50 P
excess of all other reactants
25 W3P2SHF
50 S
50 W3P2SHF
50 S and excess of all other reactants

15. Solid aluminum reacts w/chlorine gas to yield solid aluminum chloride.
Al(s) Cl2(g)  AlCl3(s)
If 125 g aluminum react w/excess chlorine, how many g aluminum chloride are made?
= g AlCl3

16. If 125 g chlorine react w/excess aluminum, how many g aluminum chloride are made?
= g AlCl3
If 125 g aluminum react w/125 g chlorine, how many g aluminum chloride are made? g AlCl3
We’re out of Cl2.

17. limiting reactant (LR): the reactant that runs out first
Amount of product is based on LR.
Any reactant you don’t run out of is an excess reactant (ER).

18. Example
Limiting Reactant
Excess Reactant(s)
Big Macs
buns
meat
tricycles
pedals
W, S, H, F
Al / Cl2 / AlCl3
Cl2 Al

19. How to Find the Limiting Reactant
For the generic reaction RA RB  P
Assume that the amounts of RA and RB are given.
Should you use RA or RB in your calculations?

20. How to find LR steps… 1. Calc. # of mol of RA and RB you have.
2. Divide by the respective coefficients in balanced equation.
3. Reactant having the smaller result is the LR.