AHSGE: Science Introduction to Chemistry

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AHSGE Science Introduction to Chemistry

• Chemical Equations

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Chemical Equations

• In this tutorial you will
• Analyze a Chemical Equation
• Prove a Chemical Equation is Balanced
• Explain Reasons for Balancing Equations
• Explore Common Chemical Reactions

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Analyze a Chemical Equation
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Home

• One of the main functions of chemistry is to
  determine what will happen when substances react.

• A chemical equation is the method used to express
  what happens during a chemical reaction.
• The chemical equation below outlines a familiar
  chemical reaction. What is this telling you?

2Na Cl2 ? 2NaCl

• A chemical equation is really just a recipe.
• It tells you the amounts of specific ingredients
  that are required to make a certain amount of a
  product.

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Analyze a Chemical Equation
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• Lets take a closer look at that chemical
  equation.

2Na Cl2 ? 2NaCl
Reactants
Products
First, you should notice that the equation is
broken into two parts with an arrow.The arrow
represents the chemical reaction.
The ingredients on the left side of the
equation are called the Reactants
The results on the right side of the equation
are called the Products
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Analyze a Chemical Equation

• Identify the reactants and the products in the
  following reactions.

N2 3H2 ? 2NH3 BaCO3 ? BaO
CO2 MnO2 4HCl ? MnCl2 Cl2
2H2O
Reactants
Products
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Analyze a Chemical Equation
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• Lets take another look at that chemical equation.

2Na Cl2 ? 2NaCl
Coefficients
Subscripts
Coefficients tell the number of atoms or
molecules that are required for the reaction.
Coefficients are the amounts of the reactants
and products.
The coefficients in this equation tell usTwo
sodium atoms will react with One chlorine
molecule to produce Two molecules of sodium
chloride.
The small numbers following the chemical symbols
are called Subscripts.(Subscripts of one are
not written out.)
Subscripts tell the number of atoms that are
bonded together to makea single molecule of a
substance. They determine the substance itself.
The subscripts in this equation tell us Na is
in elemental form.2 Cl atoms are bonded to form
a molecule of chlorine gas.1 Na is bonded to 1
Cl to make a molecule of sodium chloride.
You probably noticed the numbers associated with
chemical formulas for the reactants and the
products.
The large numbers in front of the formulas are
called Coefficients. (Coefficients of one are
not written out.)
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Analyze a Chemical Equation
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Home

• What do the chemical equations below tell you?

N2 3H2 ? 2NH3 (NH3 is
Ammonia) 2MgO 4Si ? 2Mg SiO2
1 molecule of nitrogen gas reacts with 3
molecules of hydrogen gas to form 2 molecules of
ammonia. Nitrogen and hydrogen molecules are
each formed from 2 atoms bonded together.
Ammonia is formed from 1 N atom bonded to 3 H
atoms.
2 molecules of Magnesium Oxide (each with 1Mg
bonded to 1 O) react with 4 atoms of silicon to
form 2 atoms of magnesium and 1 molecule of
silicon dioxide (having 1 Si bonded to 2 O)
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1 of 6
Prove a ChemicalEquation is Balanced
Home
Remember coefficients of 1 are not written out.

• An equation must be balanced to be useful.

• The equation below is not balanced. Can you see
  what is missing?

2
2
1
Na Cl2 ? NaCl

• There are no coefficients in the equation above.
• Coefficients determine the amounts of reactant
  and product.
• The amounts of reactant and product are correct
  when the coefficients make the equation balance.

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Prove a Chemical Equation is Balanced

• Prove the equation is balanced.

2Na Cl2 ? 2NaCl
Na
2
2
Cl
2
2
Remember, a balanced chemical equation has the
same type and number of atoms on both the
reactant and product sides.
We need to keep track of types and numbers of
atoms on each side of the equation. SoLets
get organized by creating a table
First Identify the all of the different
elements that are involved in this
reaction.There are 2 types of atoms Sodium
Chlorine
Second Count the number of atoms of each type
on the reactant side.You will consider both
coefficients subscripts
The lack of a subscript and the coefficient of
2 on sodium, tells us that there are 2 Na atoms
on the reactant side.
The subscript of 2 and the lack of a coefficient
on chlorine, tells us that there is one molecule
of chlorine that contains 2 Cl atoms.
Third Count the number of atoms of each type
on the product side.You will consider both
coefficients subscripts
The Coefficient of 2 and the lack of subscripts,
tells us there are 2 molecules of sodium
chloride. Each molecule has 1 Na and 1 Cl.
This gives a total of two sodium atoms and two
chlorine atoms on the product side.
This reaction is balanced because there are same
number and types of atoms on each side.
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Prove a Chemical Equation is Balanced

• Prove the equation is balanced.

MnO2 4HCl ? MnCl2 Cl2 2H2O
Mn
1
1
O
2
2
4
H
4
Cl
4
2
4
This reaction is balanced because there are same
number and types of atoms on each side.
MnCl2 tells us there is one molecule that has 1
manganese bonded to 2 chlorines.So, there is 1Mn
atom and 2 Cl atoms.
Chlorine shows up in two products MnCl2 Cl2.
Cl2 tells us there is 1 molecule of chlorine gas
with 2 Cl atoms bonded together.
There are a total of 4 chlorine atoms on the
product side of the equation 2 from the MnCl2
and 2 from the Cl2.
Remember, a balanced chemical equation has the
same type and number of atoms on both the
reactant and product sides.
We need to keep track of types and numbers of
atoms on each side of the equation. SoLets
get organized by creating a table
First Identify the all of the different
elements that are involved in this
reaction.There are 4 types of atoms Mn, O, H,
Cl
Second Count the number of atoms of each type
on the reactant side.You will consider both
coefficients subscripts
MnO2 tells us that there is one molecule of this
compound and it has one manganese bonded to two
oxygens.
4HCl tells us that there are four molecules each
having one hydrogen bonded to one chlorine.So
there are four hydrogen and four chlorine.
Third Count the number of atoms of each type
on the product side.You will consider both
coefficients subscripts
2H2O tells us that there are two molecules each
having one oxygen bonded to two hydrogens.So
there are four hydrogen and two Oxygen
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4 of 6
Prove a Chemical Equation is Balanced

• Prove the following reaction is balanced.

2NO 2CO ? N2 2CO2
N
2
2
4
O
4
2
2
C
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5 of 6
Prove a Chemical Equation is Balanced

• Prove the following reaction is balanced.

P4O10 4HNO3 ? 4HPO3 2N2O5
P
4
4
22
O
22
4
4
H
N
4
4
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Prove a Chemical Equation is Balanced
Home

• Prove the following reaction is balanced.

C6H12O6 6O2 ? 6CO2 6H2O
C
6
6
12
H
12
18
18
O
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Explain Reasons forBalancing Equations
Home

• You know that a reaction is balanced when the
  coefficients make the number and type of atoms on
  each side of the equation equal.

2Na Cl2 ? 2NaCl

• You can also prove whether a reaction is
  balanced.
• But why is it so important to balance an
  equation?
• Why wouldnt you want to write the equation like
  this Na Cl2 ? NaCl
• There are at least three reasons why it is
  important to balance a chemical reaction.

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Explain Reasons forBalancing Equations

• Look at the unbalanced equation below.

Na Cl2 ? NaCl
2
2
Na
Na
Notice there are two chlorine atoms on the
reactant side but only 1 chlorine on the product
side.
Where did that other chlorine go?It has to go
somewhere. It cant just disappear.This leads
us to a very important law in chemistry.
The Law of Conservation of Matter.This law
states that matter can not be created or
destroyed only changed in form.
This means if we start with two atoms of chlorine
we must end with two atoms of chlorine.
The unbalanced equation above suggests that an
atom of chlorine just disappeared.This is
against the law.
When the proper coefficients are in place and
the equation is balanced, all the atoms can be
accounted for.
Now we are following The Law of Conservation of
Matter.
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Explain Reasons forBalancing Equations

• Look at the partially balanced equation below.

2Fe 3H2O ? Fe2O3
H2
3
Fe
Fe
O-Fe-O-Fe-O
H-H
H-H
H-H
Notice in this partially balanced equation that
the iron and the oxygen are balanced.
However, the hydrogens from water on the reactant
side are not accounted for on the product
side.Where did those hydrogen atoms go?
As it turns out, the hydrogen atoms bonded
together to form another product Hydrogen Gas
(H2)
If a chemical equation is not properly balanced,
you may miss a potential product.
Hydrogen gas is odorless and colorless but
explosive.Thats not a product you would want to
overlook.
What coefficient in front of the H2 would make
this equation balance?
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Explain Reasons forBalancing Equations

• What does the unbalanced reaction below tell you?

Na Cl2 ? NaCl
2
2
Na
Na
Cl-Cl
Na-Cl
Na-Cl
Remember, chemical equations are recipes. They
tell the amounts of the ingredients required and
the amounts of product you can expect.
This reaction, as written, tells you that sodium
atoms (Na) react with chlorine gas molecules
(Cl2) to form molecules of sodium chloride (NaCl)
We know the ingredients and products but we
dont know how much of each is needed.
The amounts of each substance are determined by
the coefficients that are assigned when the
equation is balanced.
Balancing the equation tell us how much of each
reactant is required and how much of each product
will be produced.
An unbalanced equation is like a recipe that
tells you all the ingredients but doesnt tell
you how much of each one to use
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Explain Reasons forBalancing Equations
Home

• Why is it important to work with a balanced
  chemical equation?

• If an equation isnt balanced, it implies that
  atoms suddenly appear or disappear. This goes
  against the Law of Conservation of Matter
• If an equation isnt balanced, you may miss a
  product that is not easily observed.
• An equation is a chemical recipe. If it isnt
  balanced, it is like a recipe that doesnt
  include any amounts. It would be useless to try
  to make something from such a recipe.

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Explore Common Chemical Reactions
Home

• A chemical reaction is a recipe that lists
  amounts and type of both reactants and products.

• In this section you will analyze common chemical
  reactions.
• The goal is to give you the background
  information necessary to determine the type of
  product when given the reactants.
• There are seven of these reactions. You have
  already had experience with some of them.
• The following slides will present each of these
  common chemical reactions.

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Explore Common Chemical Reactions

• Salt Formation

Metal Nonmetal ? Salt
Na Cl2 ? NaCl
2
2
Fe O2 ? Fe2O3
2
3
4
Metals combine with nonmetals to form salts. A
specific example is shown above with sodium metal
reacting with chlorine gas.
There is a special case of this type of
reaction.Metals react with Oxygen (a nonmetal)
to form a Metal Oxide (a salt)
Metals combining with oxygen is also called
corrosion or oxidation. This reaction can be a
costly one because degrades metal objects.
In the specific example above, Iron reacts with
Oxygen to form Iron III Oxide. Which is
commonly known as rust.
Most metal objects must be protected from oxygen
so this reaction doesnt occur. This is one
reason for painting metal objects.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

Mg O2 ?
MgO
2
2
Metal
Nonmetal
? Salt
(Metal Oxide)
(Oxygen)
Mg (magnesium) is a metal. O2 (oxygen) is a
nonmetal.Metals combine with nonmetals to form
salts.
In this case, the salt that forms will be a
metal oxide because the nonmetal is oxygen.
The product is Magnesium Oxide (MgO)Mg takes on
a 2 charge O is 2.So one Magnesium balances
one Oxygen.
The chemical equation is balancedwith the
coefficients shown above.
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Explore Common Chemical Reactions

• Base Formation

Metal Oxide Water ? Base
Na2O
H2O
? NaOH
You now know that a metal oxide is a salt.It is
composed of a metal bonded to oxygen.You also
know water is H2O.
Remember a base is type of compound that has a
metal bonded to the Hydroxide Ion (OH 1).Here,
the metal is sodium (Na1)
The base that is formed is Sodium Hydroxide.Na
has a 1 charge OH has a 1 charge so the
formula is NaOH. (one Na with one OH)
Bases represent an important class of compounds.
When you hear the term caustic or alkaline, it is
probably in reference to a base.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

CaO H2O ?
Ca(OH)2
Metal Oxide
Water
? Base
CaO (calcium oxide) is a Metal Oxide. H2O is
Water.Metal Oxides combine with water to form
bases.
The product is Calcium Hydroxide (Ca(OH)2)Ca
takes on a 2 charge OH is 1.So one Calcium
balances two Hydroxide ions.
The chemical equation is balancedas it is shown
above.
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Explore Common Chemical Reactions

• Acid Formation

NonmetalCompound
Water ? Acid
SO3
H2O
? H2SO4
Nonmetal compounds are two or more nonmetals
covalently bonded.You also know water is H2O.
Remember an acid is type of compound that has a
Hydrogen ion(s) bonded to a nonmetal.Here, the
nonmetal is the sulfur trioxide (SO3)
The acid that is formed is Sulfuric Acid.H has a
1 charge SO4 has a 2 charge. The
formula is H2SO4. (two H with one SO4-2)
Acids are another important class of compounds.
You have heard of various acids stomach acid,
acid rain, battery acid, acetic acid (vinegar),
citric acid (in fruits), ascorbic acid (vitamin
C), etc
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

CO2 H2O ?
H2CO3
NonmetalCompound
Water
? Acid
CO2 (carbon dioxide) is a nonmetal compound. H2O
is Water.Nonmetal compounds combine with water
to form acids.
The product is Carbonic Acid (H2CO3)H takes on a
1 charge CO3 is 2.So two Hydrogens balance
one Carbonate ion.
The chemical equation is balancedas it is shown
above.
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Explore Common Chemical Reactions

• Neutralization

Acid Base ? Salt Water
HCl
NaOH
? NaCl
HOH
An acid releases hydrogen H1 ions.A base
releases hydroxide OH-1 ions.The acid in this
case is HCl. The base is NaOH.
A salt is a metal bonded to a nonmetal. The
metal is the Na1 from the base.The nonmetal is
the Cl-1 from the acid. These ions form the salt
NaCl
The water forms from the remaining ions. The H1
(from the acid) bonds to the OH-1 (from the
base). This makes H-OH or H2O (water).
The H ions of acids and the OH- ions of bases
make them very reactive compounds.But when they
react together, the H ions and the OH- ions bond
tightly to each other.
This forms water which is very stable.The acid
and the base neutralize each other.This
reaction is often called neutralization.
When you take an antacid for an upset stomach,
what you are really doing is neutralizing your
stomach acid with a base (the antacid).
You probably also noticed that in this reaction
the pairs atoms traded partners. The H from the
acid bonded to the OH from the base.The Na from
the base bonded to the Cl from the acid.
The pairs of atom replaced each other to form
two new substances.This type of reaction is
sometimes called a double replacement reaction.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

HCl Mg(OH)2 ?
MgCl2
HOH
2
2
Acid
Base
? Salt Water
One product, the salt, is Magnesium Chloride
(MgCl2)Mg takes on a 2 charge Cl is 1.So,
one Magnesium balances two Chlorines
The other product, the water, is H-OHThe H (from
the acid) takes on a 1 charge.The OH (from the
base ) has a 1 charge.So, water is HOH or H2O.
The chemical equation is balancedwith the
coefficients shown above.
HCl is an acid. Mg(OH)2 is a base. Acids react
with bases to form a Salt and Water.
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Explore Common Chemical Reactions

• Metal Plating

1st Metal Salt ? 2nd Metal Salt
Zn
CuSO4
? Cu
ZnSO4
You can see the original metal (the zinc), took
the place of the copper in the salt. We started
with Copper II Sulfate ended with Zinc Sulfate.
The zinc replaced the copper. This type of
reaction is often called a single replacement
reaction.
This type of reaction is very common.It is found
in batteries and metal plating.However, it will
only occur if the original metal is more reactive
than the metal in the salt.
Zinc is more reactive than copper so this
reaction will take place.If copper metal was
placed in a solution of zinc sulfate, nothing
would happen.
The metal is in solid elemental form.The salt is
dissolved water as ionsThe metal here is Zn.
The salt is CuSO4.
The second metal (product) comes from the metal
portion of the original salt.
The salt that is produced is formed from the
original metal and the nonmetal portion of the
original salt.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below. (Magnesium is more reactive than
  Silver)

Mg AgNO3 ?
Ag
Mg(NO3)2
2
2
Metal 1
Salt
? Metal 2 Salt
One product, the metal, is Silver (Ag)The silver
was replaced by the magnesium. Mg donated its
e- becoming a Mg2 ion.The Ag1 ions accepted
the e- and went back to elemental form.
The other product, the salt, is Mg(NO3)2The
magnesium is now an ion Mg2 and with two
nitrate ions NO3-1 forms a new salt. (Magnesium
Nitrate)
The chemical equation is balancedwith the
coefficients shown above.
Mg is a metal. Ag(NO3)2 is a salt. Metals can
react with salts producing a new salt by
replacing the metal.
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Explore Common Chemical Reactions

• Combustion

Carbon Dioxide
Organic Compound
Water
Oxygen ?
CH4
O2
? CO2
H2O
2
2
The chemical equation is balancedwith the
coefficients shown above.
Organic compounds contain carbon.In this case,
it is methane gas (CH4) Oxygen is simply Oxygen
Gas (O2)
One product is Carbon Dioxide (CO2)The other
product is Water (H2O)
This is a reaction that you encounter daily.
The reaction of organic compounds with oxygen
to produce carbon dioxide and water is called
combustion.
Another word for combustion is burning.This
reaction allows us to release energy from organic
fuel sources.
These fuels may be the gasoline in your car, the
natural gas that heats your home, coal, oil or
the food you eat to power your body.The basic
reaction is the same for each.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

C3H8 O2 ?
CO2
H2O
3
5
4
Carbon Dioxide
OrganicCompound
Oxygen ?
Water
There is an additional product in combustion
reactions and that is energy.The production of
energy is the reason we burn these fuels.
The chemical equation is balancedwith the
coefficients shown above.
C3H8 (propane) is an organic compound.It reacts
with oxygen in a combustion reaction to form
carbon dioxide and water.
The two products in any combustion reaction are
always Carbon Dioxide and Water.
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Explore Common Chemical Reactions

• Polymerization

Monomer Monomer ? Polymer
C2H3Cl
C2H3Cl
? -C2H3Cl-C2H3Cl-
A monomer is a relatively small molecule.The
monomers in this example are vinyl chloride
molecules C2H3Cl
Small molecules are bonded together to form
larger molecules. The groups of monomers are
called polymers.
The polymer that is formed in this case is a
chain of vinyl chloride molecules.It is called
Polyvinyl Chloride (PVC).
The process of putting small molecules (monomers)
together to form larger molecules (polymers) is
called polymerization.
The process of polymerization is used to make
create synthetic substances like plastics, nylon,
styrofoam, etc.
Polymerization is also used by living
things.Proteins are polymers of amino acids.
Starch and cellulose are polymers of simple
sugars.
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Explore Common Chemical Reactions

• What product would be formed from the reactants
  listed below.

C2F4 C2F4 ?
-C2F4-C2F4-
Polymer(Teflon)
Monomer(Tetrafluoroethylene)
Monomer ?
The product is Teflon.It is a polymer of the
small C2F4 monomers.
C2F4 are monomers. Monomers combine to form
Polymers.
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Name Salts with Multivalent Metals
Home

• Write the general reactants and products

Metal Nonmetal ? Salt
Metal Oxide Water ? Base
Nonmetal Compound Water ? Acid
Acid Base ? Salt Water
Metal 1 Salt ? Metal 2 Salt
Organic Oxygen ? Carbon
WaterCompound Dioxide
Monomer Monomer ? Polymer
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AHSGE Science Introduction to Chemistry

• You have Completed
• Chemical Equations