Stoichiometry
WE BE COOKING….
Stoichiometry
 Deals with the chemistry of quantifying chemical
reactions through the use of:




Balancing equations
Moles (mol)
Molarity (mol/L)
Mass (grams)
Cooking…
 A recipe is used to make a dish…let’s say brownies
½ cup butter
2 oz of chocolate
1 cp sugar
2 eggs
1 tsp vanilla
2/3 cp flour
½ tsp baking powder
¼ tsp salt
24 Brownies
What if I want 36 Brownies
 The ingredients don’t change but the amount does
proportionally…
½ cup butter
2 oz of chocolate
1 cp sugar
x by 1.5
2 eggs
1 tsp vanilla
2/3 cp flour
½ tsp baking powder
¼ tsp salt
¾ cup butter
3 oz of chocolate
1.5 cp sugar
3 eggs
1.5 tsp vanilla
1 cp flour
¾ tsp baking powder
1/8 tsp salt
Recipes are just like chemical equations
2Mg(s) + O2(g)  2MgO(s)
2 mol of Mg + 1 mol of O2 yields 2 moles of MgO
If I want 6 moles of MgO…I need 6 mol of Mg and 3
moles of O2.
Proportions…
Wait…wait…proportion? That means conversion!!
What…DA?
Coefficients are Conversion Factors
2KClO3(s)  2KCl(s) + 3O2(g)
Conversions:
2 mol KClO3 = 2 mol KCl
2 mol KClO3 = 3 mol O2
2 mol KCl = 3 mol O2
Coefficients from
balanced equation
Question:
How many moles of oxygen gas is produced if there is 4.56
moles of KClO3 present?
4.56 mol KClO3
3
mol O2
2
mol KClO3
= 6.84 mol of O2
So what does this mean…
 From previous knowledge:
 Liters to moles (Molarity)
 Mass to moles (molar mass)
 Now…
 Moles to moles (using coefficients)
 We can not only work with one particular
compound/molecule/atom…now we can work with
multiple compounds/molecules/atoms
 All aboard to moleland!!
Let’s put this knowledge into action..
2KClO3(s)  2KCl(s) + 3O2(g)
How many gramsMolar
of KCl is produced if 6.89 gramsMolar
of KClO3
Coefficients
are decomposed?
mass of
mass of
KClO3
KCl
6.89 g KClO3 1 mol of KClO3
122.55 g of KClO3
2 mol KCl
74.55 g of KCl
2 mol KClO3
1 mol of KCl
= 4.19 g of KCl
Review Steps for Stoiching…
 Write and balancing chemical reaction
 Start with given (mass, moles, or volume)
 Convert to moles (if mass and volume is given)
 Moleland!!
 Convert to moles of another compound/atom
 Convert to final unit (moles/grams/volume)
Working with molarity
Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)
How many grams of copper will be required to completely
mass
replace silver from 208 mL of 0.100Coefficients
M solution ofMolar
AgNO
3?
of Cu
208 mL
1L
1000 mL
0.100 mol AgNO3 1 mol Cu
1L
2 mol AgNO3
= 0.661 g of Cu
63.546 g Cu
1 mol Cu
Reasons for Stoichiometry
 Quantify how much you need to start with
 Without throwing in any amount willy nilly
 Quantify how much you make
 Determine how baller you are
 Quantify how much you have left over
More Practice
Lead(II) nitrate solution reacts with 27.5 mL of 3.00 M
carbonic acid, H2CO3(aq), how many grams of lead(II)
carbonate is produced?
Pb(NO3)2(aq) + H2CO3(aq)  PbCO3(s) + 2HNO3(aq)
Coefficients
27.5 mL
1L
1000 mL
Molar mass
of PbCO3
3.00 mol H2CO3 1 mol PbCO3 267.21 g PbCO3
1L
1 mol H2CO3
= 22.0 g of PbCO3
1 mol PbCO3
More Practice
Solid limestone, calcium carbonate, is heated to produced
solid CaO and carbon dioxide gas. How much limestone is
required to produce 10.0 grams of calcium oxide?
CaCO3  CaO(s) + CO2(g)
Molar mass
of CaO
10.0 g CaO 1 mol CaO
56.077 g CaO
Coefficients
Molar mass
of CaCO3
1 mol CaCO3
100.085 g CaCO3
1 mol CaO
1 mol CaCO3
= 17.8 g of CaCO3