1. Stoichiometry Notes

2. Stoichiometry
By combining our abilities to balance equations and do simple unit conversions, we can now complete stoichiometry problems (mass to mass conversions)

3. Stoichiometry
Stoichiometry problems consist of predicting the amount of grams of product that will form from a reaction if you know how many grams of reactant you have, or predicting the number of grams of reactant that will be needed to produce a certain amount of product.

4. Stoichiometry As an example, let’s consider a ham sandwich
To make a ham sandwich, here is the equation:
1 H(am) + 2 B(read) + 1 L(ettuce)→1 HB2L (also known as a Ham Sandwich)

5. Stoichiometry
If you had 4 slices of ham, 6 pieces of lettuce, and 7 slices of bread, how many ham sandwiches could you make?
(remember 1 H + 2 B + 1 L → 1 HB2L)
This problem is the same as a stoichiometry problem.

6. Stoichiometry
How about how many pieces of bread would you need to make 14 ham sandwiches?
This is another type of problem that you’ll do in stoichiometry

7. Stoichiometry
We will solve these problems using a “T” chart just like we did for unit conversions, but we will add additional cells
Given info Units to convert into Units to convert into etc
Units to cancel Units to cancel etc
and we use additional conversion factors

9. How would you determine how many ham sandwiches you could make if you had 16 g of bread?
Ham = 2.1 g per slice
Lettuce = 1.8 g per slice
Bread = 2.4 g per slice

10. Stoichiometry The additional factors we will use include:
___ moles of Y = ___ moles of Z
where the coefficients in a balanced equation gives us the numbers that replace the blank spots

11. Stoichiometry 2. 1 mole = (molar mass) # of grams
Density (# of grams/L) = 1 Liter of solid, liquid, or aqueous solution (or L if density is given in mass/mL or mass/cm3)
22.4 Liters of any gas (at STP)= 1 mole
1 mole = x 1023 parts (atoms, ions, molecules, etc)
STP = standard temperature and pressure

12. Stoichiometry grams X A moles X C moles Y A grams Y D E B B E D
liters X atoms X atoms Y liters Y
A: 1 mole = (molar mass) # of grams
B: 1 mole = x 1023 parts (atoms, ions, molecules, etc)
C: (Coefficient of balanced equation) moles X = (Coefficient of balanced equation) moles Y
D: Density: (# of grams) = 1 Liter of solid, liquid, or aqueous solution (or L if density is given in mass/mL or mass/cm3)
E: Liters of any gas (at STP)= 1 mole

13. Stoichiometry
Practice problems p. 375, 376, 377

14. Limiting and Excess Reactants
Let’s return to the ham sandwich example.
(remember 1 H + 2 B + 1 L → 1 HB2L)
If you have 4 pieces of ham, 6 pieces of lettuce, and 7 slices of bread, how many leftover pieces of ham and lettuce will you have?
This is known as a limiting reactant problem

15. Limiting and Excess Reactants
Here’s another example:

16. Limiting and Excess Reactants

17. Limiting and Excess Reactants
Once the limiting reactant has been determined, you can use it to calculate how much of the other reactants will be consumed, and how much of the products will be produced.
To determine how much will be left over, simply subtract the consumed/produced amounts from the available amounts.

18. Limiting and Excess Reactants
Do practice problems #23 and 24 on pg. 383

19. Limiting and Excess Reactants
Stoichiometry Pizza Exercise (on handout)
Find out how many pizzas you can make using the amount of each ingredient
Whichever ingredient makes the least pizzas is the limiting reactant.

20. Percent Yield
You can also use stoichiometry calculations to determine percent yield in a reaction.
The amount that you actually get may be more or less than the amount that you would predict in a stoichiometry problem.
If you divide the actual yield by the theoretical yield (predicted), you can determine the % yield.

21. Percent Yield
Do practice problems #29, 30 on p. 387