Transcript Chapter 12.1 PPT

Stoichiometry
The Arithmetic of Equations
Prentice-Hall Chapter 12.1
Dr. Yager
Objectives

Explain how balanced equations apply to
both chemistry and everyday situations.

Interpret balanced chemical equations in
terms of moles, representative particles,
mass, and gas volume at STP.

Identify the quantities that are always
conserved in chemical reactions.
A balanced chemical equation provides the
same kind of quantitative information that a
recipe does.
Here is the Problem!
Cupcake Recipe for 10 cupcakes:
• 2 eggs
• 3 cups of flour
• 1 cup sugar
You have:
• 3 eggs
• 4 cups of flour
• 2 cups of sugar
What limits the number of cupcakes you can make?
The original recipe is: 2:3:1
2 eggs, 3 C flour, 1 C sugar
Given:
3 eggs, 4 C flour, 2 C sugar
1. 3 eggs requires:
4.5 cups of flour and 1.5 cups of sugar
2. 4 cups of flour requires:
2 2/3 eggs and 1 1/3 cups of sugar
3. 2 cups of sugar requires:
4 eggs and 6 cups of flour
The only one possible is #2!
The Chemist:
Uses the ratio or balanced equation to calculate
how much reactant is needed or product
formed.
The calculation of quantities in chemical
reactions is a subject of chemistry called
stoichiometry.
Stoichiometry

Defined as the calculation of quantities in
chemical reactions

Form of bookkeeping for chemists

Generally, one of the reactants limits the
calculations
An equation can represent the manufacturing
of a single tricycle.
A balanced chemical equation can be interpreted in
terms of different quantities, including numbers of
atoms, molecules, or moles; mass; and volume.
Interpreting Chemical Equations
N2(g) + 3H2(g)
2NH3(g)
Atoms, Molecules, etc..
Moles
Mass
Volume
What is Conserved?

Mass and atoms are conserved.

Molecules, formula units, moles and volumes
are not necessarily conserved.

Example where they are conserved:
H2(g) + I2(g)
2HI(g)
Balance and Tell What is Conserved
C2H2 (g) + O2 (g)
CO2 (g) + H2O(g)
2C2H2 (g) + 5O2 (g)
4CO2(g) + 2H2O(g)
Atoms – Yes
Molecules – No
Moles – No
Mass - Yes
Formula Units – No
Volume – No
1. A manufacturer of bicycles has 5350
wheels, 3023 frames, and 2655
handlebars. How many bicycles can
be manufactured using these parts?
a) 2675 bicycles
b) 2655 bicycles
c) 3023 bicycles
d) 5350 bicycles
1. A manufacturer of bicycles has 5350
wheels, 3023 frames, and 2655
handlebars. How many bicycles can
be manufactured using these parts?
a) 2675 bicycles
b) 2655 bicycles
c) 3023 bicycles
d) 5350 bicycles
2. A reaction that produces iron metal from iron ore:
Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g)
What is the volume of gas at STP that reacts and the
volume of gas at STP produced?
a) 3 L and 4 L.
b) 67.2 L and 89.6 L.
c) 67.2 L and 67.2 L
d) 3 L and 3 L
2. A reaction that produces iron metal from iron ore:
Fe2O3•H2O(s) + 3CO(g)  2Fe(s) + 3CO2(g) + H2O(g)
What is the volume of gas at STP that reacts and the
volume of gas at STP produced?
a) 3 L and 4 L.
b) 67.2 L and 89.6 L.
c) 67.2 L and 67.2 L
d) 3 L and 3 L
3. What is conserved in this reaction?
H2(g) + Cl2(g)  2HCl(g)
a) only mass
b) only mass and number of moles
c) only mass, number of moles, and
number of molecules
d) mass, number of moles, number
of molecules, and volume
3. What is conserved in this reaction?
H2(g) + Cl2(g)  2HCl(g)
a) only mass
b) only mass and number of moles
c) only mass, number of moles, and
number of molecules
d) mass, number of moles, number
of molecules, and volume