Download Chemical Reactions

Chemical Reactions
Describing Chemical Reactions
• Word equations
• Chemical equations
Word Equations
• Describe a chemical reaction in writing
• In a reaction one or more substances
(reactants) change into one or more new
substances (products)
• REACTANTS
PRODUCTS
• This is the shorthand used in chemistry
•
means “yeilds”, “gives”,
“produces”
Chemical Equations
• Their Job: Depict the kind of
reactants and products and their
relative amounts in a reaction.
4 Al (s) + 3 O2 (g)  2 Al2O3 (s)
• The numbers in the front are called
stoichiometric coefficients
• The letters (s), (g), and (l) are the
physical states of compounds.
Chemical Equations
• This is quicker and more efficient than
word equations
• In chemical equations the arrow separates
the formulas of the reactants from the
formulas of the products
• Example: Fe + O2
Fe2O3
• You should notice something wrong…
Chemical Equations
• Fe + O2
Fe2O3
• This is a skeleton equation
• Shows formulas of reactants and
products, but NOT the amounts of
each
• If you look at the reaction, the Law
of Conservation of Matter is NOT
obeyed!
• Won’t use these much!
• We MUST balance the equation
Chemical Equations
• Before we can balance, we need to know
some symbols
Symbols used in Chemical Equations
• the arrow
separates the
reactants from the products
– Read as “reacts to form” or “yields”
• The plus sign (+) = “and”
• (s) after the formula = solid: AgCl(s)
• (g) after the formula = gas: CO2 (g)
• (l) after the formula = liquid: H2O (l)
Symbols used in Equations
 (aq) after the formula = dissolved in
water, an aqueous solution: NaCl(aq) is
a salt water solution
 ↑ used after a product indicates a gas
has been produced: H2↑
 ↓ used after a product indicates a solid
has been produced: PbI2↓
Practice on whiteboards
• Write skeleton equation for…
1. Solid iron (III) sulfide reacts with
gaseous hydrogen chloride to form iron
(III) chloride and hydrogen sulfide gas.
2. Nitric acid dissolved in water reacts
with solid sodium carbonate to form
liquid water and carbon dioxide gas and
sodium nitrate dissolved in water.
Practice on whiteboards
Solid iron (III) sulfide reacts with gaseous
hydrogen chloride to form iron (III) chloride
and hydrogen sulfide gas.

Fe2S3 + HCl (g)  FeCl3 + H2S (g)
Nitric acid dissolved in water reacts with solid
sodium carbonate to form liquid water and
carbon dioxide gas and sodium nitrate
dissolved in water.

HNO3 (aq) + Na2CO3(s)  H2O (l) + CO2 (g) + NaNO3 (aq)
Now, write these in words…
Fe(s) + O2(g)  Fe2O3(s)
Cu(s) + AgNO3(aq)  Ag(s) + Cu(NO3)2(aq)
Pt
NO2 (g)   N2(g) + O2(g)
Balanced Chemical Equations
Because of the principle of the
conservation of matter,
an equation must be
balanced.
It must have the same
number of atoms and the
same kinds of atoms
both sides.
Lavoisier, 1788
Balanced Reactions
• Atoms can’t be created or
destroyed:
–All the atoms we start with we must
end up with
• A balanced equation has the
same number of each element on
both sides of the equation.
Subscripts vs. Coefficients
• The subscripts
tell you how
many atoms of
a particular
element are in a
compound.
• The coefficient
tells you about
the quantity, or
number, of
molecules of
the compound.
Chemical Equations
4 Al(s) + 3 O2(g)  2Al2O3(s)
This equation means
4 Al atoms + 3 O2 molecules
---produces--->
2 molecules of Al2O3
AND/OR
4 moles of Al + 3 moles of O2
---produces--->
2 moles of Al2O3
• Never change a subscript to balance an
equation.
– If you change the formula you are describing a
different reaction.
– H2O is a different compound than H2O2
• Never put a coefficient in the middle of a
formula
2NaCl is okay, but Na2Cl is not.
Steps to Balancing Equations
There are four basic steps to balancing a chemical equation.
1. Write the correct formula for the reactants and the
products. DO NOT TRY TO BALANCE IT YET! You
must write the correct formulas first. And most
importantly, once you write them correctly DO NOT
CHANGE THE FORMULAS (that is, mess with the
subscripts)
2. Find the number of atoms for each element on the left
side. Compare those against the number of the atoms
of the same element on the right side.
3. Determine where to place coefficients in front of
formulas so that the left side has the same number of
atoms as the right side for EACH element in order to
balance the equation.
4. Check your answer to see if:
– The numbers of atoms on both sides of the
equation are now balanced.
– The coefficients are in the lowest possible whole
number ratios. (reduced)
Some Suggestions to Help You
Some Helpful Hints for balancing equations:
MINOH- “Me Know Chemistry” Tarzan says.
• Take one element at a time
– Start w/ Metals first
– Then Ions – specifically polyatomic ions
» (Shortcut) Polyatomic ions that appear on both sides of the
equation should be balanced as independent units (don’t
break them down into individual elements)
– Then Nonmetals…Cl and S are most common
– Then Oxygen and Hydrogen
• IF everything balances except for O, and there is no
way to balance O with a whole number, double all
the coefficients and try again. (This tends to occur
b/c O is diatomic as an element…so watch that)
H2 +O2  H2O
After writing the correct chemical formula for each
reactant and product, balancing of the equation is then
accomplished by placing coefficients in front of the
appropriate chemical species. The coefficient 'multiplies'
the number of each atom for a particular formula unit in
order to balance the equation.
H 2 + O 2  H2 O
• When balancing chemical equations,
coefficients are added in front of a
particular species indicating multiple
numbers of that species. Do not change
subscripts since this actually changes the
identity of the intended reactant or product
• H2O is water
• H2O2 is hydrogen
peroxide
• They are very
different!
Balancing Equations
2 H2(g) + ___ O2(g) ---> ___
2 H2O(l)
___
What Happened to the Other
Oxygen Atom?????
This equation is not balanced!
Two hydrogen atoms from a hydrogen
molecule (H2) combine with one of the
oxygen atoms from an oxygen molecule
(O2) to form H2O. Then, the remaining
oxygen atom combines with two more
hydrogen atoms (from another H2 molecule)
to make a second H2O molecule.
Balancing
Equations
2 Al(s) + ___
3 Br2(l) ---> ___ Al2Br6(s)
___
Balancing
Equations
__C3H8(g) + ___ O2(g) ___CO2(g) + __H2O(g)
___B4H10 (g) + ___O2 (g) ___B2O3 (g) + ___ H2O (g)
Balancing Equations
Sodium phosphate + iron (III) oxide 
sodium oxide + iron (III) phosphate
__Na3PO4 + __Fe2O3 __Na2O + __ FePO4
Practice Balancing Examples
• _AgNO3 + _Cu  _Cu(NO3)2 + _Ag
• _Mg + _N2  _Mg3N2
• _P + _O2  _P4O10
• _Na + _H2O  _H2 + _NaOH
• _CH4 + _O2  _CO2 + _H2O
More Balancing Practice
•
•
•
•
Handout
Worksheet (do 30 of the 50)
This is homework if not completed in class
We will have a balancing pop quiz 1 or two
times during this unit.
Types of Chemical Reactions
• There are millions of reactions.
• We can’t remember them all, but luckily
they will fall into several categories.
• We will learn 5 major types.
• Will be able to predict the products.
• For some, we will be able to predict
whether or not they will happen at all.
Types of Reactions
•
There are five types of chemical
reactions we will talk about:
1.
2.
3.
4.
5.
•
Synthesis reactions
Decomposition reactions
Single displacement reactions
Double displacement reactions
Combustion reactions
You need to be able to identify the type
of reaction and predict the product(s)
Steps to Writing Reactions
•
Some steps for doing reactions
1. Identify the type of reaction
2. Predict the product(s) using the type of reaction
as a model
3. Balance it
Don’t forget about the diatomic elements!
(BrINClHOF) For example, Oxygen is O2 as an
element.
In a compound, it can’t be a diatomic element
because it’s not an element anymore, it’s a
compound!
1. Synthesis reactions
• Synthesis reactions occur when two
substances (generally elements) combine and
form a compound. (Sometimes these are
called combination or addition reactions.)
reactant + reactant  1 product
• Basically: A + B  AB
• Example: 2H2 + O2  2H2O
• Example: C + O2  CO2
Synthesis Reactions
• Here is another example of a synthesis
reaction
Practice
• Predict the products. Write and balance
the following synthesis reaction equations.
• Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
• Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
• Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
2. Decomposition Reactions
• Decomposition reactions occur when a
compound breaks up into the elements or
sometimes into simpler compounds
• 1 Reactant  Product + Product
• In general: AB  A + B
• Example: 2 H2O  2H2 + O2
• Example: 2 HgO  2Hg + O2
Decomposition Reactions
• Another view of a decomposition reaction:
Decomposition Exceptions
• Carbonates, hydroxides, and chlorates are
special case decomposition reactions that do
not go to the elements.
• Carbonates (CO32-) – give you gas… they
decompose to carbon dioxide and a metal oxide
• Example: CaCO3  CO2 + CaO
• Hydroxides (OH-) – make me wet myself…
they decompose to a water and a metallic oxide
• Example: 2 Fe(OH)3  Fe2O3 + 3 H2O
• Chlorates (ClO3-) – pop my oxygen off… they
decompose to oxygen gas and a metal chloride
(note there is no metallic oxide left but a metallic
chloride)
• Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2
Practice
• Predict the products. Then, write and
balance the following decomposition
reaction equations:
• Solid Lead (IV) oxide decomposes
PbO2(s) 
• Aluminum nitride decomposes
AlN(s) 
Practice
Identify the type of reaction for each of the
following synthesis or decomposition
reactions, and write the balanced equation:
N2(g) + O2(g)  Nitrogen monoxide
BaCO3(s) 
Co(s)+ S(s)  (make Co be +3)
NH3(g) + H2CO3(aq) 
NI3(s) 
3. Single Replacement Reactions
• Single Replacement Reactions occur when
one element replaces another in a compound.
• A metal can replace a metal (+) OR
a nonmetal can replace a nonmetal (-).
• element + compound compound* + element*
• The case of water…
When H2O splits into ions, it splits into
H+ and OH- (not H+ and O-2 !!)
Single Replacement Reactions
• Another view:
Single Replacement Reactions
• Write and balance the following single
replacement reaction equation:
• Zinc metal reacts with aqueous
hydrochloric acid
Zn(s) + 2 HCl(aq)  ZnCl2 + H2(g)
Note: Zinc replaces the hydrogen ion in the
reaction… hydrogen ion is the cation (+)
Single Replacement
• We can even tell whether or not a
single replacement reaction will
happen:
– Some chemicals are more “active” than
others
– More active replaces less active
• There is a list called the Activity
Series of Metals
• Higher on the list replaces lower.
The Activity Series of the Metals
Higher
activity
Lower
activity
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Chromium
Iron
Nickel
Lead
Hydrogen
Bismuth
Copper
Mercury
Silver
Platinum
Gold
1) Metals can replace other
metals provided that they are
above the metal that they are
trying to replace.
2) Metals above hydrogen can
replace hydrogen in acids.
3) Metals from sodium upward
can replace hydrogen in
water.
Single Replacement Reactions
• Sodium chloride solid reacts with fluorine gas
2 NaCl(s) + F2(g)  2 NaF(s) + Cl2(g)
Note that fluorine replaces chlorine in the compound
• Aluminum metal reacts with aqueous copper
(II) nitrate
Al(s)+ Cu(NO3)2(aq)
Single Replacement video
• http://www.google.com/imgres?imgurl=http
://www.sci.brooklyn.cuny.edu/~marciano/s
repl.jpg&imgrefurl=http://www.sci.brooklyn.
cuny.edu/~marciano/Animations.htm&h=2
00&w=320&sz=19&hl=en&start=1&tbnid=
S3V2dhBgM8gdqM:&tbnh=74&tbnw=118&
prev=/images%3Fq%3Dsingle%2Breplace
ment%2Breactions%26svnum%3D10%26
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Single Replacement Practice:
• Fe + CuSO4 
• Pb + KCl 
• Al + HCl 
4. Double Replacement Reactions
• Double Replacement Reactions occur when
a metal replaces a metal in a compound and a
nonmetal replaces a nonmetal in a
compound… like switches places
• Compound + compound  product +
product
• AB + CD  AD + CB
• always involves ionic
compounds in aqueous
solutions
#4 - Double Replacement
• Has certain “driving forces”
– Will only happen if one of the
products:
a) doesn’t dissolve in water and forms a
solid (a “precipitate”), or
b) is a gas that bubbles out, or
c) is a molecular compound (usually
water).
Double Replacement Reactions
• Think about it like “foil”ing in algebra, first and
last ions go together + inside ions go together
• Example:
AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq)
• Another example:
K2SO4(aq) + Ba(NO3)2(aq) 2 KNO3(aq) + BaSO4(s)
Double Replacement Video
• http://www.google.com/imgres?imgurl=http
://www.sci.brooklyn.cuny.edu/~marciano/s
repl.jpg&imgrefurl=http://www.sci.brooklyn.
cuny.edu/~marciano/Animations.htm&h=2
00&w=320&sz=19&hl=en&start=1&tbnid=
S3V2dhBgM8gdqM:&tbnh=74&tbnw=118&
prev=/images%3Fq%3Dsingle%2Breplace
ment%2Breactions%26svnum%3D10%26
hl%3Den%26lr%3D
Practice
•
Predict the products. Balance the equation
1. HCl(aq) + AgNO3(aq) 
2. CaCl2(aq) + Na3PO4(aq) 
3. Pb(NO3)2(aq) + BaCl2(aq) 
4. FeCl3(aq) + NaOH(aq) 
5. H2SO4(aq) + NaOH(aq) 
6. KOH(aq) + CuSO4(aq) 
How to recognize which type
• Look at the reactants:
E + E = Combination/synthesis
C
= Decomposition
E+C
= Single replacement
C + C = Double replacement
5. Combustion Reactions
• Combustion reactions occur
when a hydrocarbon reacts
with oxygen gas.
• This is also called burning!!!
In order to burn something
you need the 3 things in the
“fire triangle”:
1) A Fuel (hydrocarbon)
2) Oxygen to burn it with
3) Something to ignite the
reaction (spark)
Combustion Reactions
• In general:
CxHy + O2  CO2 + H2O
• Products in complete combustion are ALWAYS
carbon dioxide and water.
• Products of incomplete combustion can be carbon
and carbon monoxide (Poisonous)
• Many times heat and light are given off as by-products
of the reaction
• Combustion is used to heat homes and run
automobiles (octane, as in gasoline, is C8H18)
Combustion
• Example
•
C5H12 + 8 O2  5 CO2 + 6 H2O
• Write the products and balance the
following combustion reaction:
•
C10H22 + O2 
Mixed Practice
•
1.
2.
3.
4.
5.
State the type, predict the products, and
balance the following reactions:
BaCl2 + H2SO4 
C6H12 + O2 
Zn + CuSO4 
Cs + Br2 
FeCO3 
Total Ionic Equations
• Once you write the molecular equation
(synthesis, decomposition, etc.), you should
check for reactants and products that are soluble
or insoluble.
• We usually assume the reaction is in water
• We can use a solubility table to tell us what
compounds dissolve in water.
• If the compound is soluble (does dissolve in
water), then splits the compound into its
component ions
• If the compound is insoluble (does NOT dissolve
in water), then it remains as a compound
Solubility Table
Solubilities Not on the Table!
• Gases only slightly dissolve in water
• Strong acids and bases dissolve in water
– Hydrochloric, Hydrobromic, Hydroiodic, Nitric,
Sulfuric, Perchloric Acids
– Group I hydroxides (should be on your chart anyway)
• Water slightly dissolves in water! (H+ and OH-)
• There are other tables and rules that cover more
compounds than your table!
Total Ionic Equations
Molecular Equation:
K2CrO4 + Pb(NO3)2 
PbCrO4 + 2 KNO3
Soluble
Insoluble
Soluble
Soluble
Total Ionic Equation:
2 K+ + CrO4 -2 + Pb+2 + 2 NO3- 
PbCrO4 (s) + 2 K+ + 2 NO3-
Net Ionic Equations
• These are the same as total ionic
equations, but you should cancel out ions
that appear on BOTH sides of the
equation
Total Ionic Equation:
2 K+ + CrO4 -2 + Pb+2 + 2 NO3- 
PbCrO4 (s) + 2 K+ + 2 NO3Net Ionic Equation:
CrO4 -2 + Pb+2  PbCrO4 (s)
Net Ionic Equations
• Try this one! Write the molecular, total ionic, and net
ionic equations for this reaction: Silver nitrate reacts
with Lead (II) Chloride in hot water.
Molecular:
What is soluble and what is not?
Total Ionic:
Net Ionic:
Review of stuff you need to know
NOMENCLATURE
•
•
•
•
•
Calcium chloride
Sodium sulfide
Aluminum oxide
Iron (III) bromide
Copper (II) oxide
•
•
•
•
•
•
•
•
Magnesium sulfate
Lead (II) nitrate
Potassium phosphate
Aluminum hydroxide
Sodium chlorate
Nitric acid
Hydrochloric acid
Sulfuric acid
Review of stuff you need to know
BALANCING
NaCl(s) + F2(g)  NaF(s) + Cl2(g)
Is this balanced?
2NaCl + F2  2NaF + Cl2
Review of stuff you need to know
REACTION TYPES
• E+EC
• C  E + E (or just more simple products)
• E1 + C1  C2 + E2
• C1 + C2  C3 + C4
• CxHy + O2  CO2 + H2O
Review of stuff you need to know
NAME TYPE, PREDICT
PRODUCTS, AND BALANCE
•
•
•
•
•
•
•
Zn + HCl 
Ag + Cl2 
NaBr 
Na3PO4 + MgSO4 
C6H6 + O2 
Fe(III) + Cl2 
MnCO3 
•
•
•
•
C7H6O + O2 
NH4Cl + KOH 
CaI2 + Br2 
Al(OH)3 
Review of stuff you need to know
WORD PROBLEMS
• Iron (III) hydroxide decomposes
• Bromine reacts with Potassium iodide
• Calcium chloride and Lead (II) nitrate react