Chemical Reactions
BELLWORK
BRIEFLY WRITE ABOUT
A SCIENTIFIC
OBSERVATION YOU
MADE RECENTLY
Chemical equations
WE USE CHEMICAL
EQUATIONS TO
DESCRIBE
CHEMICAL
REACTIONS
Burning Coal
This is a chemical reaction
The purpose of the equation is
to show what was present before
the reaction (carbon and oxygen)
and afterwards (carbon dioxide)
The substances that undergo change
are reactants (carbon and oxygen)
New substances formed as a result of
that change are called products
REACTANTS
PRODUCTS
CARBON + OXYGEN
DIOXIDE
SIMPLIFY:
C+O2
CARBON
CO2
CHEMICAL EQUATION
A CHEMICAL EQUATION IS
A REPRESENTATION OF A
CHEMICAL REACTION IN
WHICH THE REACTANTS
AND PRODUCTS ARE
EXPRESSED AS FORMULAS.
CONSERVATION OF MASS
THE LAW OF THE CONSERVATION OF MASS:
MASS IS NEITHER CREATED NOR DESTROYED
IN A CHEMICAL REACTION
ALTHOUGH THE MASS OF THE COAL WAS
REDUCED DURING THE REACTION, IT WAS
NOT LOST
THE MASS OF THE CARBON DIOXIDE
CREATED WAS EQUAL TO THE MASS OF THE
COAL THAT WAS LOST
BALANCING EQUATIONS
ACCORDING TO THE LAW OF
CONSERVATION OF MASS,
EACH SIDE OF AN EQUATION
MUST BE EQUAL
H2 + O2
H2O
TO BALANCE WE SIMPLY ADD
COEFFICIENTS:
THE NUMBERS THAT APPEAR BEFORE
THE EQUATION
H 2 + O2
H2 O
H 2 + O2
2H2O
=
WHAT IS WRONG WITH THIS EQUATION?
HOW CAN WE FIX IT?
ANSWER
2H2 + O2
2H2O
WHICH MEANS:
TWO MOLECULES OF
HYDROGEN REACT WITH ONE
MOLECULE OF OXYGEN TO
YIELD TWO MOLECULES OF
WATER
http://PHSchool.com/webcodes10/index.cfm?wcprefi
x=ccp&wcsuffix=1071&area=view&x=13&y=7
MATH SKILLS
READ OVER THE MATH
SKILLS EXAMPLES AND
STEPS FOR BALANCING
EQUATIONS ON PAGE
195
THEN, TRY THE MATH
Balancing equations tutorials
http://www.youtube.com/watch?v=RnGu3xO2h74
http://www.youtube.com/watch?v=gskm-dfKv5g
BELLWORK
BALANCE THE
FOLLOWING CHEMICAL
EQUATION:
H2+O2 H2O
WHAT ARE SOME UNITS OF MEASURE THAT
YOU KNOW OF?
A. What is the Mole?
A counting number (like a dozen)
Avogadro’s number (NA)
1 mol = 6.02  1023 items
A
large amount!!!!
Counting with Moles
MOLE: (MOL) AN AMOUNT OF A
SUBSTANCE THAT CONTAINS
APPROXIMATELY 6.02 X 1023
PARTICLES OF THAT SUBSTANCE.
KNOWN AS AVOGADRO’S NUMBER
A MOLE OF A SUBSTANCE
GENERALLY CONTAINS 6.02 X 1023
ATOMS, MOLECULES, OR IONS OF
THAT SUBSTANCE
A. What is the Mole?
n
1 mole of hockey pucks would
equal the mass of the moon!
n
1 mole of basketballs would fill a
bag the size of the earth!
1 mole of pennies would cover the Earth 1/4 mile
deep!
Molar Mass
THE MASS OF DIFFERENT
ELEMENTS ARE DIFFERENT,
AS IS THEIR MOLAR MASS
THE MOLAR MASS OF AN
ELEMENT IN THE SAME AS ITS
ATOMIC MASS EXPRESSED IN
GRAMS
MASS OF COMPOUNDS
YOU CAN FIND THE MASS OF
COMPOUNDS BY ADDING THE
MASS OF THEIR COMPONENTS
A CARBON DIOXIDE MOLECULE:
CARBON= 12 GRAMS
OXYGEN = 16 GRAMS X 2 = 32
GRAMS
12 + 32 = 44 GRAMS
LETS TRY
MOLAR MASS OF C
MOLAR MASS OF Fe
MOLAR MASS OF H2O
MOLE-MASS
CONVERSIONS
TO FIND HOW MANY
MOLES ARE IN A CERTAIN
# OF GRAMS OF AN
ELEMENT OR MOLECULE:
Y GRAMS x
moles
1/z grams= x
Example
WE HAVE 55 GRAMS OF CO2
HOW DO WE FIND HOW MANY
MOLES WE HAVE?
55 X 1 mol/44 g
1 mol/44 g=.02272727 mol
.02272727mol X 55 g = 1.25 mol CO2
BELLWORK
WHAT IS A MOLE?
WHY DO WE USE MOLES?
HOW MUCH IS ONE MOLE
OF BARIUM IN GRAMS?
CARBON DIOXIDE?
WATER?
REVIEW:
A mole is just a number, nothing
else
That number is 6.02 x 1023
We use this number to make
otherwise incredibly small
numbers (such as the mass of an
atom) easy to use in chemical
Review
There are two conversions we will do
with moles:
Find how many moles there are
in a certain number of grams
(mass) an element or molecule
Find the the number of grams
(mass) there are in a certain
number of moles of an element or
molecule
Two conversion factors
a)
Grams
1 Mol
1 Mol
Grams
b)
or
How many grams, use conversion
factor a
Practice
Suppose we have 55 grams of CO2
How do we find how many moles of CO2
there are in 55 grams of CO2?
Step 1: find the molar mass of CO2
44 grams/mole
Step 2: set up the equation
55 grams CO2 x 1 mol CO2 = ? mol
CO2
44 grams CO2
Step 3: Solve the equation
55 grams CO2 x 1 mol CO2 = ? mol CO2
44 grams
CO2
1/44= .0227
55 x .0227 = 1.25
There are 1.25 moles of CO2 in 55 grams of
Flip it!
Now, suppose we have 2.4 moles of sulfur.
How do we find how many grams there
are in 2.4 moles of sulfur?
Step 1: Find the molar mass of sulfur.
32.07 grams/mole
Step 2: Set up the equation:
2.4 moles x 32.07 grams S = ? Grams S
1 mol S
Step 3: solve the equation:
2.4 x 32.07 = 77 grams sulfer
There are 77 grams of sulfur in 2.4 moles of sulfur
Get into the groups I assigned
the other day.
Work on the worksheet together.
Do as many problems as you can.
Types of Chemical Reactions
http://www.youtube.com/watch?v=i-HHvx1VC_8
http://www.youtube.com/watch?v=nsEkKIiOz7Q
7.2 Types of Chemical Reactions
Just like states of matter, you can classify
chemical reactions based on reactants and
products.
Types:
Synthesis
Decomposition
Single-replacement
Double replacement
Combustion
Flip Book Time!
Make a flip book for the different types of
chemical reactions.
You should have 6 flaps, 1 title and 5
different reactions
Each flap should have:
The type of reaction (Synthesis)
Definition/explanation
Real example (Sodium reacts with chlorine to produce sodium chloride)
Chemical example (A + B -> AB)
Finished?
Complete your workbook up
to section 7.2
We will have an open note
quiz over balancing chemical
equations and mole
conversions tomorrow.
Synthesis
Reaction where two or more substances
react to form a single substance.
A + B -> AB
Reactants may be elements or compounds
Examples: sodium reacts with chlorine to
make sodium chloride
Chemical Example: 2NA + Cl2 -> 2NaCl
Synthesis
Synthesis
DECOMPOSITION
A COMPOUND BREAKS DOWN INTO TWO
OR MORE SIMPLER SUBSTANCES
AB -> A + B
REACTANTS MUST BE COMPOUNDS
PRODUCTS MAY BE COMPOUNDS OR
ELEMENTS
EXAMPLE: WATER DECOMPOSES INTO
HYDROGEN AND OXYGEN GAS WHEN
ELECTRICITY IS PASSED THROUGH IT
2H2O -> 2H2 + O2
Decomposition
Decomposition
SINGLE REPLACEMENT
REACTION WHERE ONE ELEMENT
TAKES THE PLACE OF ANOTHER IN A
COMPOUND
A + BC -> B + AC
EXAMPLE: COPPER WIRE IS DIPPED
INTO SILVER NITRATE AND WATER.
COPPER REPLACES THE SILVER IN
SILVER NITRATE TO FORM COPPER (II)
NITRATE.
Cu + 2 AgNO3 -> 2Ag + Cu(NO3)2
Double Replacement
Two different compounds exchange
positive ions and form two new
compounds
AB + CD -> AD +CB
Example: Lead (II) nitrate and
potassium iodide (colorless). Yellow
precipitate forms
Pb(NO3)2 + 2KI -> PbI2 + 2KNO3
Combustion
A substance reacts rapidly with
oxygen, often producing heat
and light
Example: burning of natural gas
CH4 + 2O2 -> CO2 + 2H2O
Oxidation - Reduction
A reaction in which electrons are transferred from one
reactant to another is a oxidation-reduction reaction
Oxidation and reduction always occur together
It can involve full transfers, or partially charged
elements.
Oxidation
Any process in which an element loses electrons during
a chemical reaction is oxidation
Reduction
The process in which an element gains electrons
during a chemical reaction is called reduction.
Reactants are said to be reduced if they gain electrons
Bellwork
What is all involved in a
chemical equation?
Reactants
Products
Energy
7.3 Energy Changes in
Reactions
Key concepts:
What happens to chemical
bonds during a chemical
reaction?
What happens to energy
during a chemical reaction?
Example
Lighting a gas grill, this is a chemical reaction
What are the reactants?
Propane and oxygen
What are the products?
Carbon dioxide and water
What else is there?
Heat!
Where does the heat come from?
Chemical energy is stored in the
chemical bonds of a substance.
Chemical reactions involve the
breaking of chemical bonds in the
reactants and the formation of
chemical bonds in the products
Combustion of Propane
*During the combustion of propane the
bonds in propane and oxygen molecules
are broken, while the bonds in carbon
dioxide and water molecules are formed.
Breaking bonds
8 C-H, 5 O=O
2 C-C
6 C=O 8 O-H
Breaking bonds
Breaking bonds requires
energy
This is why a propane
grill must have an
igniter, to provide
energy to get the
Forming Bonds
Once the bonds of the reactants are
ignited, the bonds are broken, a chemical
reaction occurs, and products come
together.
The products created from a chemical
reaction are bonded together
Energy is released when these bonds are
created.
This energy is heat and light.
Question
Does breaking bonds
require energy or release
energy?
It requires energy.
Review
In an Endothermic reaction
(such as freezing) energy is
released into the surroundings
In an Exothermic reaction (such
as melting) energy is absorbed
from the surroundings.
Exothermic/Endothermic
Reactions
During a chemical reaction,
energy is either released or
absorbed
A chemical reaction that
releases energy into its
surroundings is an exothermic
Exothermic
Exothermic reactions
release more energy than is
required to break the bonds
of the reactants
Combustion is an example
of an exothermic reaction
Exothermic
In any reaction, the chemical energy reaches a
peak before the reactants change into
products.
For example, at room temperature the propane
molecules and oxygen molecules will not
collide with enough energy to cause a reaction
They need the help/heat/energy of a spark to
begin the reaction
Exothermic
In your book on pg 208, figure
A shows a graph that describes
the reaction process.
The equation is written
A+B-> AB J
Endothermic Reactions
A chemical reaction that absorbs
energy from its surroundings is an
endothermic reaction
In an endothermic reaction, more
energy is required to break the bonds
in the reactants than is released by the
formation of the products.
Endothermic
Look at 208, figure B
You can see the difference between the
reactants and products
Decomposition is a type of endothermic
reaction
The equation is written
A + B J -> AB
Conservation of Energy
The total amount of energy
before and after the reaction is
the same.
Complete 7.3 in your workbook
for homework or in class if we
have time
7.4 Reaction Rates
Reaction Rates: the rate at which
reactants change over time
Factors that affect reaction rates
include temperature, surface
area, concentration, stirring, and
catalysts.
Temperature
Generally, an increase in temperature
will increase the rate of reaction
In most cases, an increase in
temperature will increase the speed of
particles, which will increase the number
of collisions, which will increase the rate
of reaction
Surface Area
The smaller the particle size of a given
mass, the larger the surface area.
(newspaper in a room)
An increase in surface area increases the
exposure of reactants to one another
The greater this exposure, the more
collisions
Stirring
Stirring reactants increases the reaction
rate by increasing the exposure of
reactants to each other.
Concentration
The more reactants present, the greater
the opportunities for collisions.
The reaction rate is faster
With gases, concentration
increases/decreases with pressure
The greater the pressure, the greater its
concentration, the faster the reaction
rate.
Catalyst
A substance (chemical) that affects the
reaction rate in a reaction
The catalyst is neither a reactant or
product
Catalyst are able to change the
environment so that the particles will
collide with enough energy to react
faster
http://www.youtube.com/watch?v=OttRV5ykP7A
Temperature
http://www.youtube.com/watch?v=fBtCTcRYEUk
Surface area
http://www.youtube.com/watch?v=FBF7auCMy58
Concentration
http://www.youtube.com/watch?v=kjKyEdrVXJA
Catalyst
http://www.youtube.com/watch?v=hNl5WYSM5DE
Class/Homework
On your own or with a partner:
Read the section on equilibrium.
Answer the questions in your
workbook.
We will briefly go over equilibrium
tomorrow
We will have an open note quiz over
section 7.3-7.5 on Thursday
Equilibrium
Equilibrium: is a state in which the
forward and reverse paths of a change take
place at the same rate
Because there are both physical and
chemical changes that matter may
undergo, there are both physical and
chemical equilibrium
Physical
Physical equilibrium: when a physical
change does not go to completion, a
physical equilibrium is established
between the forward and reverse
changes
Water in a bottle H2O(l)
H2O(g)
Chemical
Chemical equilibrium: when
a chemical reaction does not
go to completion, a chemical
equilibrium is established
between the forward and
reverse reactions.
Factors Affecting Chemical
Equilibrium
When a change is introduced to
a system in equilibrium, the
equilibrium shifts in the
direction that relieves the
change.
Factors: temperature, pressure,
concentration
Temperature
Example: N2(g) + 3H2(g)
2NH3(g) + Heat (J)
Synthesizing (making) ammonia, heat is written as a product. This is
exothermic, it releases heat
This means that the reverse, the decomposition of ammonia, is
endothermic…it absorbs heat
What happens, then, if we add heat to a system involving ammonia?
The rule of chemical equilibrium states that equilibrium will shift towards
the direction that removes that change (increased temperature)
Which direction in this reaction removes ammonia?
Would we then have more or less ammonia if we increase the temperature?
Pressure
Example: N2(g) + 3H2(g)
2NH3(g) + Heat (J)
If you add pressure to a system, the equilibrium would shift in the
direction that decreases pressure.
The system would favor the direction that produces fewer gas
molecules.
Which side has fewer gas molecules?
The right has fewer
So, adding pressure to this system would create more ammonia
Concentration
Example: N2(g) + 3H2(g)
2NH3(g) + Heat (J)
The same rule applies to concentration.
If we remove ammonia from this reaction, the equilibrium would
shift in the direction that makes ammonia.
The opposite would be true if we added ammonia, the
equilibrium would then shift to the side that decomposes
ammonia.
http://www.youtube.com/watch?v=g5wNg_dKsYY