1. Stoichiometry

2. What is Stoichiometry? The quantitative study of a chemical reaction.
A chemical reaction is like a recipe.
You need to make brownies.
1 pkg mix + 2eggs + ¼ cup oil →24brownies
What if you need 48 brownies?

4. What is Stoichiometry? 2H2 + O2 →2H2O
2 molecules H2 + 1 molecule O2 → 2 molecules H2O
2 moles H2 + 1 mole O2 → 2 moles H2O
mole ratio
4g H g O2 → 36 g H2O

5. Mole - Mole
1. How many moles of H2 are needed to react with 3.5 mol O2? 2H2 + O2 →2H2O 3.5 mol O2 x 2 mol H2 = 7.0 mol H2 1 mol O2 B) How many moles of water are produced?

6. Practice
2. How many moles of KClO3 must decompose to produce 9.0 moles of O2? 2KClO3 → 2KCl + 3O2 6 mol KClO3

7. Mass – Mole
3. How many grams of CO2 are produced by the combustion of mol of butane (C4H10)?
2 C4H O2 → 8CO2 + 10H2O
0.750 mol x g
0.75 mol C4H10 8 molCO2
2 mol C4H10
0.75 mol C4H mol CO g CO2
2 mol C4H mol CO2
= 132 g

8. Example
4. How many moles of Fe2S3 are produced by reacting 50.0 g of Fe with S?
mol

9. Mass - Mass
5. How many grams of water are produced by the combustion of 1.00 g of C6H12O6?
C6H12O6 + 6O2 → 6CO2 + 6H2O
1.00 g x g
1.00 g C6H12O6 1 mol C6H12O mol H2O g H2O
180 g C6H12O mol C6H12O6 1 mol H2O
= g

10. Examples
6. 4NH3 + 7 O2 → 4NO2 + 6H2O
122 g x g
194 g

11. Examples
7. How many molecules of HCl are produced by reacting 125 g of chlorine with hydrogen?
2.12 x1024 molecules

12. Steps to solve Stoichiometry Problems
Write the balanced equation.
Show what you are given and what you are trying to find.
Convert what you are given to moles.
Multiply by the mole-mole ratio (coefficients).
Convert to what you are trying to find.

13. Limiting Reactant
The reactant that is completely used up in a reaction.
Determines the amount of product formed.
Excess reactant – reactant that is left over (too much) does not affect the amount of product formed.

14. Limiting Reactant 1. We need to make a turkey sandwich.
2 slices bread + 1 piece of turkey→ 1 sandwich
20 slices pieces ?
How many sandwiches can we make? 10
What is the limiting reactant?
Bread
How much turkey will be left over?
5 pieces

15. 2. What if we had 20 slices of bread and 6 pieces of turkey?
How many sandwiches could we make? 6
What is the limiting reactant?
turkey
How much bread would be left over?
8 slices

16. Limiting Reactant 1) Mg + I2 → MgI2 3 mol 4 mol What is the LR? Mg
After the reaction is complete: How many moles of Mg?
0 moles Mg
Moles of I2?
1 mol I2
Moles of MgI2?
3 mol MgI2

17. Limiting Reactant 2) 2Al + 3Br2 → 2AlBr3 LR? Br2
4.0 mol mol
LR?
Br2
After the reaction is complete: How many moles of Br2?
0 mol Br2
Moles of AlBr3?
2.7 mol AlBr3
Moles of Al? (Honors)
1.3 mol Al

18. Limiting Reactant 3) N2 + 3H2 → 2NH3 LR?
4.0 mol mol
LR?
To determine LR: divide # moles by the coefficient
N2: 4.0 mol/1= 4.0
H2: mol/3 = 3.3
H2 is LR. This number is only used to determine LR. Always use moles of LR in the stoichiometry calculations.

19. Limiting Reactant How many moles of NH3 are formed? 6.7 mol NH3
(Honors) Calculate the number of moles of N2 left over.
0.7 mol N2

20. Limiting Reactant 4) HCl + NaOH → H2O + NaCl 10.0g 10.0g LR?
Convert grams to moles
HCl g 1mol = mol HCl
36.5 g
NaOH g 1 mol = 0.25 mol NaOH
40 g
NaOH is LR

21. Limiting Reactant Calculate the number of grams of NaCl formed.
Use the # moles of the LR
0.25 mol NaOH 1 mol NaCl g NaCl
1 mol NaOH 1 mol NaCl
= g NaCl

22. Limiting Reactant
(Honors)Calculate the number of grams of HCl left over.
First calculate the # g of HCl that are used in the reaction.
0.25 mol NaOH 1 mol HCl g HCl
1 mol NaOH 1 mol HCl
= 9.13 g HCl used
10.0 g – 9.13 g = 0.9 g HCl left over

23. Limiting Reactant 5) Zn + 2HCl → ZnCl2 + H2 50.0g 42.0g LR? HCl
Calculate the # grams of ZnCl2 formed.
78.2 g
(Honors)Calculate the # grams of Zn left over.
12.6 g