Transcript Types of Chemical Reactions

Chapter 3
Chemical Reactions
Chemical Change Evidence
Chapter 6
Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
a)
b)
c)
d)
The color changes.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
“Colorless hydrochloric acid is added to
a red solution of cobalt(II) nitrate, turning
the solution blue.”
a)
b)
c)
d)
The color changes.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
Chemical Change Evidence
What is a clue that a chemical reaction has
occurred?
“A solid forms when a solution of sodium
dichromate is added to a solution of lead
nitrate.”
a)
b)
c)
d)
A gas forms.
A solid forms.
Bubbles are present.
A flame is produced.
Chapter 6
Chemical Reactions
• A chemical equation is an abbreviated way to
show a chemical or physical change
• A chemical change alters the physical and
chemical properties of a substance
• Factors that indicate a chemical change




Change in color
Temperature change
Change in odor
Change in taste (we do not taste chemicals)
• Reactions always contain an arrow that
separates the reactants from the products
Reactants
Products
Chapter 6
Types of Chemical Reactions
•
Combination reaction (synthesis)


Elements for reactants
Examples:
H2 + O2
N2 + H2
Al + O2
H2O
NH3
Al2O3
The Law of Conservation of matter,
states matter cannot be created nor
destroyed, the means equations must be
balanced.
Types of Chemical Reactions
Balance the first equation
H2 + O2
H2O
Note two oxygen atoms on the reactant
side and only one on the product side,
therefore place a two in front of water
Types of Chemical Reactions
Balance the first equation
H2 + O2
2H2O
Note two oxygen atoms on the reactant
side and only one on the product side,
therefore place a two in front of water
The two now doubles everything in water,
thus 4 hydrogen and 2 oxygen. Now
place a 2 in front of hydrogen.
Types of Chemical Reactions
Balance the first equation
2H2 + O2
2H2O
Note two oxygen atoms on the reactant
side and only one on the product side,
therefore place a two in front of water
The two now doubles everything in water,
thus 4 hydrogen and 2 oxygen. Now
place a 2 in front of hydrogen.
Types of Chemical Reactions
Now balance the second equation
N2 + H2
NH3
Note two nitrogen atoms on the reactant side
and only one on the product side.
Place a 2 in front of ammonia
Types of Chemical Reactions
Now balance the second equation
N2 + H2
2NH3
Note two nitrogen atoms on the reactant side
and only one on the product side.
Place a 2 in front of ammonia. This makes 2
nitrogen atoms and 6 hydrogen atoms. Now
place a 3 in front of hydrogen to balance
hydrogen atoms.
Types of Chemical Reactions
Now balance the second equation
N2 + 3 H2
2NH3
Note two nitrogen atoms on the reactant side
and only one on the product side.
Place a 2 in front of ammonia. This makes 2
nitrogen atoms and 6 hydrogen atoms. Now
place a 3 in front of hydrogen to balance
hydrogen atoms.
Types of Chemical Reactions
• Decomposition Reaction
 Compounds form simpler compounds or
elements.
 Examples
H2O
H2 + O2
Types of Chemical Reactions
• Decomposition Reaction
 Compounds form simpler compounds or
elements.
 Examples
2H2O
H2 + O2
Types of Chemical Reactions
• Decomposition Reaction
 Compounds form simpler compounds or
elements.
 Examples
2H2O
2H2 + O2
• Notice decomposition reactions are the
opposite of combination reactions
Types of Chemical Reactions
Single Replacement reactions have an element and a
compound for reactants.
Example:
Zn + HCl
How do we predict the products? Trade places
with the metal or nonmetal with the metal or
nonmetal in the compound
Types of Chemical Reactions
Single Replacement reactions have an element
and a compound for reactants.
Example:
Zn + HCl
How do we predict the products? Trade
places with the metal or nonmetal with the
metal or nonmetal in the compound
Types of Chemical Reactions
Single Replacement reactions have an element and
a compound for reactants.
Example:
Zn + HCl
ZnCl + H
Now make the products stable. Slide with Clyde
Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + HCl
ZnCl2 + H2
Now make the products stable. Slide with
Clyde
Types of Chemical Reactions
Single Replacement reactions have an element and
a compound for reactants.
Example:
Zn + HCl
ZnCl2 + H2
Now make the products stable. Slide with Clyde
Now Balance
Types of Chemical Reactions
Single Replacement reactions have an
element and a compound for reactants.
Example:
Zn + 2HCl
ZnCl2 + H2
Now make the products stable. Slide with
Clyde
Now Balance
Types of Chemical Reactions
Single Replacement reactions have an element
and a compound for reactants.
Another Example:
Cl2 + MgBr2
How do we predict the products? Trade places
with the metal or nonmetal with the metal or
nonmetal in the compound. In this case we are
trading nonmetals
Types of Chemical Reactions
Single Replacement reactions have an element
and a compound for reactants.
Another Example:
Cl2 + MgBr2
Br +
MgCl
How do we predict the products? Trade places
with the metal or nonmetal with the metal or
nonmetal in the compound. In this case we are
trading nonmetals
Types of Chemical Reactions
Single Replacement reactions have an element
and a compound for reactants.
Another Example:
Cl2 + MgBr2
Br2 + MgCl2
How do we predict the products? Trade places
with the metal or nonmetal with the metal or
nonmetal in the compound. In this case we are
trading nonmetals
Types of Chemical Reactions
Double Replacement reactions contain compounds as
reactants.
HCl + Ca(OH)2
CaCl
+ HOH
Check formulas, and slide with Clyde when necessary
Types of Chemical Reactions
Double Replacement reactions contain compounds
as reactants.
HCl + Ca(OH)2
CaCl2 + HOH
Check formulas, and slide with Clyde when necessary
Types of Chemical Reactions
Double Replacement reactions contain compounds
as reactants.
2HCl + Ca(OH)2
CaCl2 + 2HOH
Check formulas, and slide with Clyde when
necessary
Now Balance!
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
H2 + O2
CH4 + O2
What is the oxide of hydrogen?
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
H2 + O2
CH4 +O2
What is the oxide of hydrogen? Water
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
H2 + O2
CH4 + O2
H 2O
What is the oxide of hydrogen? Water
And the oxide of carbon?
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
H 2 + O2
CH4 + O2
H 2O
CO2
+ H2O
What is the oxide of hydrogen? Water
And the oxide of carbon? Carbon dioxide
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
2H2 + O2
CH4 + O2
Now balance
2H2O
CO2 + H2O
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
2H2 + O2
CH4 + O2
Now balance
2H2O
CO2 + 2H2O
Types of Chemical Reactions
Combustion Reactions occur when an element or
compound combine with oxygen to produce oxides of
each element.
2H2 + O2
CH4 + 2O2
Now balance
2H2O
CO2 + 2H2O
The Chemical Package
About Packages
• The baker uses a package called the dozen.
All dozen packages contain 12 objects.
• The stationary store uses a package called a
ream, which contains 500 sheets of paper.
• So what is the chemistry package?
The Chemical Package
About Packages
• The baker uses a package called the dozen.
All dozen packages contain 12 objects.
• The stationary store uses a package called a
ream, which contains 500 sheets of paper.
• So what is the chemistry package? Well, it is
called the mole (Latin for heap).
Each of the above packages contain a number of
objects that are convenient to work with, for that
particular discipline.
The Mole
A mole contains 6.022X1023 particles, which is the number
of carbon-12 atoms that will give a mass of 12.00 grams,
which is a convenient number of atoms to work with in the
chemistry laboratory.
The atomic weights listed on the periodic chart are the
weights of a mole of atoms. For example a mole of
hydrogen atoms weighs 1.00797 g and a mole of carbon
atoms weighs 12.01 g.
Moles of Objects
Suppose we order a mole of marshmallows for a
chemistry party. How much space here at Central
would be required to store the marshmallows?
Moles of Objects
Suppose we order a mole of marshmallows for a
chemistry party. How much space here at Central
would be required to store the marshmallows?
Would cover the entire 50 states 60 miles deep
Moles of Objects
Suppose we order a mole of marshmallows for a
chemistry party. How much space here at Central
would be required to store the marshmallows?
Would cover the entire 50 states 60 miles deep
How about a mole of computer paper instead
of a ream of computer paper, how far would
that stretch?
Moles of Objects
Suppose we order a mole of marshmallows for a
chemistry party. How much space here at Central
would be required to store the marshmallows?
Would cover the entire 50 states 60 miles deep
How about a mole of computer paper instead
of a ream of computer paper, how far would
that stretch? Way past the planet Pluto!
Formula Weight Calculation
To calculate the molar mass of a compound we sum
together the atomic weights of the atoms that make up
the formula of the compound. This is called the formula
weight (MW, M).
Formula weights are the sum of atomic weights of
atoms making up the formula.
The following outlines how to find the formula weight of water
symbol
H
O
number
weight
= 2.02
1.01 X
2
1
= 16.0
X
16.0
18.0 g/mole
Percent Composition
Find the formula weight and the percent composition of
glucose (C6H12O6)
symbol
C
H
O
%C =
weight
number
12.0 x 6 = 72.0
1.01 x 12 = 12.12
16.0 x 6 = 96.0
180.1 g/mole
72.0
X = 40.0 %C
180.1
%H = 12.12
180.1
96.0
%O =
180.1
X = 6.73 %H
X =
53.3 %O
Law of Conservation of Mass
• The law of
conservation of
mass states that the
sum of the masses of
the reactants of a
chemical equation is
equal to the sum of
the masses of the
products.
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca
2. How many Cu atoms are present in 15.0 g of
copper?
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca
2. How many Cu atoms are present in 15.0 g of
copper?
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
2. How many Cu atoms are present in 15.0 g of
copper?
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
= 0.490 mole Ca
2. How many Cu atoms are present in 15.0 g of
copper?
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
= 0.490 mole Ca
2. How many Cu atoms are present in 15.0 g of
copper?
15.0 g Cu
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
= 0.490 mole Ca
2. How many Cu atoms are present in 15.0 g of
copper?
15.0 g Cu Mole Cu
63.546 g Cu
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
= 0.490 mole Ca
2. How many Cu atoms are present in 15.0 g of
copper?
15.0 g Cu Mole Cu
6.022X1023 atoms Cu
63.546 g Cu Mole Cu
Mole Calculations
1. How many moles of Ca atoms are present in
20.0 g of calcium?
20.0 g Ca Mole Ca
40.078 g Ca
= 0.490 mole Ca
2. How many Cu atoms are present in 15.0 g of
copper?
15.0 g Cu Mole Cu
6.022X1023 atoms Cu
63.546 g Cu Mole Cu
= 1.42X1023 atoms Cu
Empirical Formulas
1.
2.
3.
4.
5.
Assume there is 100 g of the sample, so the percent
composition will equal the number of grams of each
element.
Convert the grams of each element into the moles of
each element with their molar mass.
Divide the smallest number of moles of an element into
the moles of each element present.
Convert the fractional ratios for each element into whole
numbers by multiplying all the ratios by the same
number.
The resulting numbers are the subscripts for the each
element in the empirical formula.
Example
Asbestos was used for years as an insulating
material in buildings until prolonged exposure to
asbestos was demonstrated to cause lung
cancer. Asbestos is a mineral containing
magnesium, silicon, oxygen, and hydrogen.
One form of asbestos, chrysotile (520.27 g/mol),
has the composition 28.03% magnesium,
21.60% silicon, 1.16% hydrogen. Determine the
empirical formula of chrysotile.
Molecular Formula
• The molecular formula can be
determined from the percent
composition and mass spectral data.
Example
A combustion analysis of an unknown compound
indicated that it is 92. 23% C and 7.82% H. The mass
spectrum indicated the molar mass is 78 g/mol. What
is the molecular formula of this unknown compound?
Combustion Analysis
CaHb + excess O2 ---> a CO2(g) + b/2 H2O
The percent of carbon and hydrogen in CaHb can be
determined from the mass of H2O and CO2 produced.
Combustion Analysis
Vitamin C is essential for the prevention of scurvy.
Combustion of a 0.2000 g sample of this carbon,
hyddrogen, oxygen compound yields 0.2998 g CO2
and 0.0819 g H2O. What is the empirical formula of
vitamin C?
Mass Spectrometry
• All Mass spectrometers separate atoms and
molecules by first converting them into ions and
then separating those ions based on the ratio of
their masses to their electric charges.
• Mass spectrometers are instruments used to
determine the mass of substances.
Mass Spectrometer
Mass Spectra
Limiting Reactants
During photosynthesis a reaction mixture of
carbon dioxide and water is converted to a
molecule of glucose.
Limiting Reagents
• The limiting reactant is completely
consumed in the chemical reaction.
 The amount of product formed depends on
the amount of limiting reagent available.
Example
10.0 g of methane (CH4) is burned in 20.0 g of oxygen
(O2) to produce carbon dioxide (CO2) and water
(H2O).
a. What is the limiting reactant?
b. How many grams of water will be produced?
Percent Yield
• Theoretical Yield: the calculated
amount of product formed
• Actual Yield: the measured amount of
product formed
• Percent Yield =
100%
Actual Yield
x
Theoretical Yield
Percent Yield Example
Aluminum burns in bromine liquid producing
aluminum bromide. In a certain experiment, 6.0 g of
aluminum was reacted with an excess of bromine to
yield 50.3 g aluminum bromide. Calculate the
theoretical and percent yields for this experiment.
The End