1. DO NOW Turn in Stoichiometry Practice, Part One handout.
Pick up Notes.
Get out periodic table and a calculator.

2. LIMITING REACTANT
Rarely are reactants in a chemical reaction present in the EXACT ratios specified by the balanced equation.
Usually one or more are in excess while one is limited.
The substance that is completely consumed in a reaction is the limiting reactant. The reaction cannot continue without more of it.
Excess reactants are the reactants that are left over, in excess.

3. LIMITING REACTANT
VIDEO
DEMO

4. LIMITING REACTANT
Example: Recipe for Chocolate Chip Cookies – yields 4 dozen cookies
2.25C flour 1 C butter 2 eggs
1t salt 1 C sugar 2 t vanilla
1t baking soda C brown sugar
3 oz. chocolate chips

5. LIMITING REACTANT
If you have the amounts listed below, what is the limiting reactant?
10 C flour 4 C butter 12 eggs
4t salt 4 C sugar 8 t vanilla
4t baking soda 4 C brown sugar
10 oz. chocolate chips
How many cookies could you make with these amounts?

6. HOW TO DETERMINE THE LIMITING REACTANT
Treat these problems as mass to mass problems and then compare the answers to determine the limiting reactant.
The limiting reactant will be the one that converted to the LESSER amount.
Example: How many grams of CO2 are formed if 10.0 grams of C are burned in 20.0 g of O2.
C O2  CO2
1 mole C mole O2  1 mole CO2

7. HOW TO DETERMINE THE LIMITING REACTANT
Do the math just like you did with the mass to mass problems.
Only this time you are doing two.
One for 10.0 g of carbon and one for 20.0 g of O2.

8. HOW TO DETERMINE THE LIMITING REACTANT
10.0 g C 1 mole C 1 mole CO g CO g C 1 mole C 1 mole CO2 = __________g CO g O2 1 mole O2 1 mole CO g CO g O2 1 mole O2 1 mole CO2 = __________gCO2

9. HOW TO DETERMINE THE LIMITING REACTANT
10.0 g C forms g CO2
AND
20.0 g O2 forms g CO2
Carbon forms more product and is left over.
So, oxygen is the limiting reactant and 27.5 g CO2 is produced

10. PRACTICE
Nickel reacts with hydrochloric acid to produce nickel (II) chloride and hydrogen gas. If 5.00g nickel and 2.50g hydrochloric acid react, determine the limiting reactant and the mass of nickel (II) chloride produced.

11. PRACTICE
WYK:
EQN:
SOLVE:

12. ANSWER
Ni + 2HCl  NiCl2 + H2 5.00g Ni 1 mol Ni 1 mol NiCl g NiCl g Ni 1 mole Ni 1 mol NiCl2 = = 11.0g NiCl2 2.50g HCl 1 mol HCl 1 mol NiCl g NiCl g HCl 2 mol HCl 1 mol NiCl2 = = 4.44g NiCl2
Limiting Reactant
Amount made

13. DETERMINING EXCESS MASS
Sometimes we want to know how much of the excess was left over – in grams.
There are two steps to calculating how much is left over or “IN EXCESS”.

14. DETERMINING EXCESS MASS
Convert the grams of NiCl2 for the limiting reagent (HCl) back to grams of Ni. This will show how much Ni was actually needed.
4.44gNiCl mol NiCl mol Ni g Ni
129.59g NiCl2 1 mol NiCl mol Ni
= _____________gNi
2. Subtract this mass of Ni needed from the original amount:
5.00g Ni – 2.01g Ni = 2.99 g Ni

15. DETERMINING EXCESS MASS
Now try it for the sample problem given previously.
Find the amount of excess carbon.
Convert grams of CO2 made from oxygen back to gams of carbon.
Subtract this mass of carbon from the original amount of carbon.

16. TO DO Limiting Reactant Practice is due Monday.
There will be a quiz Monday over Stoichiometry problems (no limiting reactant).
We will also do a lab on Monday.