Transcript Chemical Reactions

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Three areas of focus
Rearranging the building
blocks of chemistry
(atoms/ions/
molecules/electrons)
 Force & energy is what
decides if the reaction
occurs and how fast
 Mathematics helps you
keep an inventory of all
the starting and ending
materials
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Recognize Evidence of a chemical change.
Represent chemical reactions with equations.
Change word equations into formula equations.
Given a description of a reaction, write a word and formula
equation.
Balance chemical equations.
Translate a formula equation into a sentence.
Define and give a description of the major types of chemical
reactions.
Classify reactions as one of five major types.
Predict the products of simple reactions when given the
reactants.
Understand, explain, and apply the activity series of the
elements.
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Memorize the diatomic elements
Memorize the symbols used in chemical equations.
Use the Activity Series for single replacement reactions
Use the Solubility Chart for Double Replacement Reactions
Know common gases
Memorize substances that decompose
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Carbonic acid, H2CO3
Sulfurous acid, H2SO3
Ammonium hydroxide, NH4OH
NH3(g)
H2CO3 (aq) H2O+ CO2(g)
H2SO3(aq)  H2O + SO2(g)
NH4OH (aq H2O +
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The process by which one or more
substances are rearranged to form
different substances is called a chemical
reaction.
Also called a chemical change
 We are making something new!
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the reactants which enter into a
reaction.
the products which are formed by
the reaction.
the relative amounts of each
substance used and each substance
produced.
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Every chemical compound has a formula
which cannot be altered.
A chemical reaction must account for every
atom that is used. This is an application of the
Law of Conservation of Matter which states
that in a chemical reaction atoms are neither
created nor destroyed.
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Production of a Gas
Temperature Change
Color Change
Production of a Solid (precipitate)
Production of Water or other unionized
substance
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chemical equations – represent
reactions
Reactants - starting Substances
Products – ending substance
 Symbols??
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The diatomic elements are always
written H2, N2, O2, F2, Cl2, Br2, I2
The sign, → , means "yields" and shows
the direction of the action.
A small delta, ( ), above the arrow
shows that heat has been added.
A double arrow, ↔ , shows that the
reaction is reversible and can go in both
directions.
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Using words in equation form to represent a
chemical reaction
iron(s) + chlorine(g) iron(III) chloride(s)
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uses chemical formulas instead of words
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Fe (s) + Cl2 (g) ----- FeCl3 (s)
Practice
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In order to obey the Law of Conservation
of Mass equations must be Balanced:
Coefficients: number written in front of a
chemical formula to indicate the smallest
number of particles involved in the reaction.
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Write skeleton equation.
Change the coefficients to make the number of
atoms of each element equal on both sides of
the equation. NEVER CHANGE A
SUBSCRIPT!!!
Write the coefficients in the smallest ratio
possible.
Check your work.
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Start with “Big Formulas” C2H6O2
Save single elements for last O2 or Cu
Balance hydrogens second to last
Balance oxygens last
Check for lowest ratio
Do not change your subscripts
Balance the polyatomic ions as one unit (if it
didn’t break apart)
Perform a final check
If your equation doesn’t
balance, check your
formulas!!
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Five Types of Chemical Reactions
Synthesis Reaction
 Decomposition Reaction
 Single Replacement Reaction
 Double replacement Reaction
 Combustion Reaction: oxygen combines
with a substance and produces heat and
light
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Synthesis Reaction: one product is
formed from more than one simpler
substances
A + B  AB
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Decomposition Reaction: One substance
is broken down into one or more simpler
substances: usually by the addition of
energy
AB  A + B
Single Replacement Reaction: atoms of
one element replace another element in a
compound
A + BC  B + AC
Double replacement Reaction: involves
the exchange of ions between two
compounds
AB + CD  AD + CB
Combustion Reaction: oxygen combines
with a substance and produces heat and
light
X + O2  H2O + CO2
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Ca + O2  CaO
Br + LiI  LiBr + I
Al + Fe(NO3)2  Al(NO3)3 + Fe
MgO + HCl  MgCl2 + H2O
C4H10 + O2  CO2 + H2O
NH4NO2  NH3 + H2O
(NH4)3PO4 + Sr(OH)2  Sr3(PO4)2 + NH4OH
H2SO4 + NaOH  Na2SO4 + H2O
Zn + AgNO3  Zn(NO3)2 + Ag
CuNO3 + KCl  KNO3 + CuCl
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Given the reactants predict what is
formed
Write formulas for reactants
 Identify the type of reaction
 Rearrange the atoms to write formulas for
products.
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Atoms of one element replace another
element in a compound
 A + BC  B + AC
There are 3 Ways
that a Single
Replacement
Reaction can occur.
when zinc combines with iron (II) chloride
the zinc replaces iron in the compound
 Z n + FeCl2  Fe + ZnCl2
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Br2 + LiI  LiBr + I2
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Use the activity series of the elements
If the free element is more active than the
element in the compound the reaction will
happen
 If the free element is below the element in
the compound the reaction will not happen
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Bigger,
stronger,
orange shirted
guy replaces
white shirt guy
in the dancing
couple
Now we have
new couple
and new single
guy
Some Examples to Observe
before lab
http://www.harpercollege.edu/tmps/chm/100/dgodambe/thedisk/se
ries/3perform.htm
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two ionic compounds are mixed together in
water
In water the ionic compounds split into
anions and cations.
The cations have an opportunity to swap
anions
A reaction occurs, if by swapping anions, a
product is formed that cannot split apart
into anions and cations
AB + CD  AD + CB
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A reaction occurs when a pair of ions
comes together to produce a substance
that removes ions from the solution.
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one of the following must occur
 a precipitate: a solid produced during a reaction
 a gas
 Water or other unionized substance
 a product that decomposes
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http://www.wisconline.com/objects/ViewObject.aspx?ID=gch1404
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What happens when one of the three possible
products is not formed?
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Nothing
All ions remain in solution (dissolved)
NaNO3(aq) + KCl(aq)� � NaCl(aq) + KNO3(aq)
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Without a driving force there is no change in
the solution so we say No Reaction has taken
place
Some double replacement reactions produce a
gas. We observe this as bubbles or odors given
off.
Example:
Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S(g)
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Some metathesis reactions do not give the product
expected.
the expected product (H2CO3) decomposes to give a
gaseous product (CO2)
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CaCO3 (s) + HCl (aq) CaCl2 (aq) + H2CO3
CaCO3 (s) + HCl (aq)  CaCl2 (aq) + CO2 (g) + H2O (l)
Products that Decompose
H2SO3  H2O + SO2
H2CO3  H2O + CO2
NH4OH  H2O + NH3
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These water molecules increase the
number of solvent molecules and we see
no observable evidence
Usually accompanied by temperature
change or
Neutralization which can be seen with an
acid base indicator
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Example: H2SO4 + NaOH  Na2SO4 + H2O
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Generally, when solutions of an acid and a base
are combined, the products are a salt and water
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HC2H3O2 (aq) + NaOH (aq) NaC2H3O2 (aq) + H2O (l)
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Acid + Base  Salt + Water
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The molecular equation lists the reactants and
products in their molecular form.
AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)
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In the ionic equation all strong electrolytes
(strong acids, strong bases, and soluble ionic
salts) are dissociated into their ions.
This more accurately reflects the species that
are found in the reaction mixture.
Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)
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To form the net ionic equation, cross out
anything that does not change from the left
side of the equation to the right.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
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The only things left in the equation are those
things that change (i.e., react) during the course
of the reaction.
Ag+(aq) + Cl-(aq)  AgCl (s)
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Those things that didn’t change (and were
deleted from the net ionic equation) are called
spectator ions.
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) 
AgCl (s) + K+(aq) + NO3-(aq)
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Write a balanced molecular equation.
Dissociate all strong electrolytes (strong acids,
strong bases, and soluble ionic salts)
Cross out anything that remains unchanged
from the left side to the right side of the
equation.
Write the net ionic equation with the species
that remain.
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Hydrocarbon + oxygen  CO2 + H2O
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Hydrocarbon: A compound of hydrogen
and carbon
The phrase "To burn" means to add
oxygen unless told otherwise.
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Complete Combustion:
Hydrocarbon + oxygen  CO2 + H2O
 Complete combustion means the higher
oxidation number is attained.
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Incomplete Combustion:
Hydrocarbon + oxygen  CO + H2O
 Incomplete combustion means the lower
oxidation number is attained.
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If oxygen is sufficient, the products are carbon
dioxide and water vapor.
If oxygen is low, carbon monoxide will be
produced.
automobile engine inside a closed garage or
charcoal grill indoors.
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Hydrocarbon
(CxHy) + O2(g) →
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CO2(g) + H2O(g)
EX. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
EX. 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
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C3H8 + O2 --> CO2 + H2O
propane 3 carbons = 3 carbon dioxide
molecules
8 hydrogen atoms = four H2O molecules.
balance the oxygen
• This combustion of
acetylene reaction
is exothermic, and
enough energy is
released to melt
metal. Used in
welding.
Why So Hot??
Triple bond
-multiple bonds
-short bond length
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Demo: Methane Snake Reaction
CH4 +
2O2
 CO2
+ 2H2O
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A + B  AB
Elem/Cmpd + Elem/Cmpd  Compound
One Product
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Metal + oxygen → metal oxide
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Nonmetal + oxygen →
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metallic hydroxide
Mg(OH)2(s)
CO2(g) + H2O(l) →
; H2CO3(aq)
2 Na(s) + Cl2(g) →
2NaCl(s)
acid
salt
A few nonmetals combine with each other
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MgO(s) + H2O(l) →
Metal + nonmetal →
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CO2(g)
nonmetallic oxide
Nonmetallic oxide + water →
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C(s) + O2(g) →
Metal oxide + water →
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2Mg(s) + O2(g) → 2MgO(s)
2P(s) + 3Cl2(g) →
2PCl3(g)
These two reactions must be remembered:
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N2(g) + 3H2(g) → 2NH3(g)
NH3(g) + H2O(l) → NH4OH(aq)
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AB  A + B
Compound Cmpd/Elem + Elem/Cmpd
One Reactant
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Metallic carbonates, when heated, form metallic oxides and
CO2(g)
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Most metallic hydroxides, when heated, decompose into
metallic oxides and water
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H2SO4 →
H2O(l) + SO3(g)
Some oxides, when heated, decompose
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2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic oxides
and water
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Ca(OH)2(s) → CaO(s) + H2O(g)
Metallic chlorates, when heated, decompose into metallic
chlorides and oxygen
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CaCO3(s) → CaO(s) + CO2(g)
2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity
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2H2O(l) → 2H2(g) + O2(g)
2NaCl(l) → 2Na(s) + Cl2(g)
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A + B  AB (synthesis)
AB  A + B (decomposition)
A + BC  B + AC
(single replacement)
AB + CD  AC + BD
(double replacement)
Hydrocarbon + oxygen CO2 + H2O
(combustion/oxidation)