Stoichiometry

1
UNIT X

• Stoichiometry

2
Obj. 1Interpreting Equations
70
28
96
40
40
216
28
96
216
70
CaCl2 AgNO3 Ca(NO3)2 AgCl
2
2
450 grams
450 grams

• mole ratio

12 12

• mole ratio of CaCl2 to Ca(NO3)2

11

• mole ratio of AgNO3 to Ca(NO3)2

21

• Check w/ Law of Cons. of Mass!

• when a chem. rxn. is properly balanced like
  this,

we can use known info. about one substance to
calculate unknown info. about another substance!

• thats stoichiometry!!!

3
Obj. 2-3Stoichiometry

• stoichiometry is a combination of

balancing equations (mole ratio - MR)
mole map MM (conversions)
dimensional analysis DA (calculation)

• stoich. uses info. about one chemical to find
  info.

about another chemical.
the only connection b/n two substances is
their MOLE RATIO

• therefore, your 1st conversion should always be

to moles!
4
Obj. 2-3 cont

• general DA rules

start grid w/ given value
same unit on top bottom of grid cancels out
top bottom values MUST each other!!!

• stoich steps

balance equation (MR)
1st conversion should be to moles (MM)
use MR to switch substances
convert new substance to desired units (MM)
x across the top, across the bottom
watch sig. digs.!!!
5
Obj. 2-3 cont

• practice

2
H2 O2 H2O
2

• mole ratio

21 2
1. How many grams of H2O will be produced from
47.9 grams of O2?
18 g H2O
1 mole O2
47.9 g O2
2 mole H2O
32 g O2
1 mole O2
1 mole H2O
53.9 g H2O
Mass Mass or M M problem!!!
6
Obj. 2-3 cont
2
H2 N2 NH3
3
31 2
1. How many grams of NH3 will be produced from
68.4 liters of H2?
17 g NH3
1 mole H2
68.4 L H2
2 mole NH3
22.4 L H2
3 mole H2
1 mole NH3
34.6 g NH3
Volume Mass or V M problem!!!
2. How many liters of N2 will be needed to react
with 59.31 liters of H2?
22.4 L N2
59.31 L H2
1 mole H2
1 mole N2
22.4 L H2
3 mole H2
1 mole N2
19.77 L N2
V V problem!!!
7
Obj. 4-5...Limiting Reactants

• we wont always get exact amounts of moles to

run experiments with.

• if one reactant runs out (is used up) before the

other, the entire rxn. stops!

• the reactant that runs out 1st is called the

limiting reactant (LR)
(limits how long the rxn. will run)

• to find your LR, calculate how many rxns. can be

run with the starting amount of reactants.
use LR to start the normal stoich. problems
8
Obj. 4-5 cont

• practice

1. if 30.0 g of NaOH and 35.0 g of H2SO4 react
together, which reactant is limiting?
two starting values given!!! ( LR prob.)
21 12
30.0g
35.0g
2
2
NaOH H2SO4 Na2SO4 H2O
23
16
1
1 rxn.
30 g NaOH
1 mole NaOH
0.375 rxn
40 g NaOH
2 mole NaOH
LR
32
64
2
1 rxn.
35 g H2SO4
1 mole H2SO4
0.357 rxn
98 g H2SO4
1 mole H2SO4
9
Obj. 4-5 cont

• practice cont

30.0g
35.0g
2
2
NaOH H2SO4 Na2SO4 H2O
1. How many liters of water will be produced?
we have already found that H2SO4 is the LR, so
we use H2SO4 to
solve this problem!!!
35 g H2SO4
2 mole H2O
22.4 L H2O
1 mole H2SO4
1 mole H2SO4
1 mole H2O
98 g H2SO4
16.0 L H2O