Transcript Document 408730

STOICHIOMETRY
(from the Greek word stoicheion, meaning
element and metron, meaning measure)
STOICHIOMETRY
(from the Greek word stoicheion, meaning
element and metron, meaning measure)
• You learned elements as the letters in chemistry
• You learned to put those letters together to make
chemical words called formulas
• You used formulas to write reactions, which can be
through of as chemical sentences
• Now you will use the chemical sentence to write a
chemical story with stoichiometry
• If you know the amount of one of those parts of the chemical
story, you know the whole rest of the story.
STOICHIOMETRY
(from the Greek word stoicheion, meaning
element and metron, meaning measure)
Is the study of the quantitative relationships that exist
in chemical reactions
Can be used to determine how much product will form
from a given amount of reactant.
The coefficients in a balanced equation indicate:
the number of moles or particles involved in the reaction.
shows the relative number of moles, not the actual numbers of moles
in the reaction (like a recipe)
Breakfast Equation
3 eggs + 1 cup milk + ½ tsp. salt + 6 slices of bread + 2 tbsp. sugar  6 slices of French toast
• What if we need to make 12 slices?
• What is the ratio of eggs to bread?
– 3:6, or 1 egg for every 2 slices of bread, so everything
needs to be doubled
So…
6 eggs + 2 cup milk+ 1 tsp. salt + 12 slices of bread + 4 tbsp. sugar  12
slices of French toast
Breakfast Equation
3 eggs + 1 cup milk+ ½ tsp. salt + 6 slices of bread +
2 tbsp. sugar  6 slices of French toast
Suppose you want to use up 10 eggs, how much
bread do you need then?
10 eggs x 6 breads = 60 breads
3 eggs
3
= 20 slices of bread
In stoichiometry, a balanced equation is used to determine the
amounts of reactants needed and the amounts of products
produced by any chemical reaction.
Stoichiometry
Calculations based on balanced equations
1.
Balance equation
2.
Identify “given” (with unit) and “?” with unit
Moles
given
Coefficient of “?”
Moles
“?”
Coefficient of
given
How many moles of hydrogen are needed to completely react with
2 moles of nitrogen?
N2 + 3 H2  2 NH3
2 moles N2 x 3 moles H2
1 mole N2
= 6.00 moles H2
Mole Relationships
.750 moles 1.50 moles
.375 moles
1.13 moles
2 PH3 + 4O2  P2O5 + 3 H2O
You are given 0.750 moles of the first reactant. Use the mole ratios
from the balanced equation to determine the moles of all the other
reagents in the reaction. What do the coefficients tell you?
4 moles O2
2 moles PH3
=
1.50 moles of O2
.750 moles PH3 X 1 mole P2O5
2 moles PH3
=
.375 moles P2O5
3 moles H20
2 moles PH3
=
1.13 moles H2O
.750 moles PH3 X
.750 moles PH3 X
C2H4 + 3 O2  2 CO2 + 2 H2O
• You are given 2.38 moles of water. How
many moles of oxygen are used in the
reaction?
2.38 moles H2O X
3 moles O2
=
2 moles H2O
3.57 moles of O2