stoichiometry introduction: mole-mole relationships
DESCRIPTION
Take a look at this “recipe” for the formation of ammonia gas. N 2 (g) + 3 H 2 (g) → 2 NH 3 (g) We can combine 1 part N 2 and 3 parts H 2 to produce 2 parts NH 3. We would typically state that we can combine 1 mole N 2 and 3 moles H 2 to produce 2 moles NH 3.TRANSCRIPT
StoichiometryIntroduction:
Mole-Mole Relationships
Significance of Coefficients
What do the coefficients in a chemical reaction represent?
Ratio of molecules that react Ratio of moles that react
Take a look at this “recipe” for the formation of ammonia gas.N2(g) + 3 H2(g) → 2 NH3(g)
We can combine 1 part N2 and 3 parts H2 to produce 2 parts NH3.
We would typically state that we can combine 1 mole N2 and 3 moles H2 to produce 2 moles NH3.
This is the recipe for making sandwiches...
What do you need to make a plain and ordinary ham sandwich?
2 Bread + 1 Ham → 1 Sandwich
Stoichiometry allows us to compare any two of the substances in a “recipe” at a time.
Typical queries might be:How many sandwiches can I prepare with 12 pieces of bread?How much bread is needed to completely use 8 slices of ham when making sandwiches?If only 4 slices of ham are in my refrigerator, how many sandwiches can I make?
How many sandwiches can I prepare with 12 pieces of bread?
2 Bread + 1 Ham → 1 Sandwich
x12 BreadBreadSandwich
21
6 Sandwiches=
How much bread is needed to completely use 8 slices of ham when making
sandwiches?
2 Bread + 1 Ham → 1 Sandwich
8 Ham x
HamBread
12
= 16 Bread
If only 4 slices of ham are in my refrigerator, how many sandwiches can I make?
2 Bread + 1 Ham → 1 Sandwich
4 Ham xHam
Sandwich=
1
14 Sandwiches
“Mole Ratio” conversion
step
Now, back to the reaction for the production of ammonia.
N2(g) + 3 H2(g) → 2 NH3(g)
How many moles of NH3 can be produced by the complete reaction of 4.0 moles of N2?
4.0 mol N2xmol N2
mol NH3
1
2=8.0 moles NH3
“Mole Ratio” conversion
step
Lets take a look at another example.
N2(g) + 3 H2(g) → 2 NH3(g)
How many moles of N2 are needed to react with 6.0 moles of H2?6.0 mol H2x
mol H2
mol N2
3
1= 2.0 moles N2
“Mole Ratio” conversion
step
A stoichiometry example with mass relationships.
N2(g) + 3 H2(g) → 2 NH3(g)
What mass of NH3 can be produced by the complete reaction of 15.0 g of H2?15.0 g H2 x
mol H2
mol NH3
2.02 2
=
84.4 g NH3
mole H2
g H2
1x
3x
mol NH3
g NH3
117.04