Download Introduction to Reactions

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Reactants  Products
Fe + O2  Fe2O3
A catalyst is a substance that speeds up the
reaction but is not changed by it.
It is neither a reactant or a product.
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Release of a gas
◦ CO2 is released when acid is placed in a solution
containing CO32- ions
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Formation of a solid (precipitate)
◦ A solution containing Ag+ ions mixed with a
solution containing Cl- ions
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Heat is produced or absorbed
◦ Acid and base are mixed together
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Color changes
Symbol

↔
(s)
(l)
(g)
(aq)




PT
Meaning
forms, produces
reversible reaction
Solid state
Liquid state; water only
Gaseous state
aqueous state, all liquids besides water
heat/energy is supplied to the reaction
Catalyst is used, here platinum
2HgO( s )

 2Hg( l ) 
O 2 (g )
Products and reactants must be
specified using chemical symbols
Reactants – written on the left of arrow
Products – written on the right
 – energy is needed
Physical states are shown in parentheses
2H2 (g) + O2(g)  2H2O(g)
Identify the substance involved
 Coefficients - how many?
 Chemical Formula – of what?
 Physical State – in what state?
 Remember Diatomic Elements
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◦ Magic Seven
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Two atoms of aluminum react with three
units of aqueous copper (II) chloride to
produce three atoms of copper and two units
of aqueous aluminum chloride?
◦ How many?
◦ Of what?
◦ What physical state?
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Two atoms of aluminum react with three
units of aqueous copper (II) chloride to
produce three atoms of copper and two units
of aqueous aluminum chloride?
◦ How many?
◦ Of what?
◦ What physical state?
2 Al(s) + 3 CuCl2(aq)  3 Cu(s) + 2AlCl3(aq)
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Describing Coefficients:
◦ individual atom = “atom”
◦ covalent substance = “molecule”
◦ ionic substance = “unit”
3CO2 
2Mg 
4MgO 
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Describing Coefficients:
◦ individual atom = “atom”
◦ covalent substance = “molecule”
◦ ionic substance = “unit”
3CO2 
3 molecules of carbon dioxide
2Mg 
2 atoms of magnesium
4MgO 
4 units of magnesium oxide
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
• How many?
• Of what?
• In what state?
Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g)
• How many?
• Of what?
• In what state?
One atom of solid zinc reacts with two units of
aqueous hydrochloric acid to produce one
unit of aqueous zinc chloride and one
molecule of hydrogen gas
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Law of conservation of mass - matter cannot
be created or destroyed
◦ mass of the products = mass of the reactants
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Coefficient: # of moles of products & reactants
◦ 4Fe + 3O2  2Fe2O3
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Diatomic elements (The Magic 7)
H2, N2, O2, F2, Cl2, Br2, I2
Coefficient - how many of that substance
are in the reaction
2HgO( s)
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

 2Hg( l )  O2 ( g )
The equation must be balanced
◦ All the atoms of every reactant must also appear in
the products
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Number of Hg on left?
2
Number of O on left?
2
◦ on right 2
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◦ on right 2
H2 + O2  H2O
 Is
the law of conservation of
mass obeyed as written?
◦ NO
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You never change subscripts
◦ WRONG: H2 + O2  H2O2
H2 + O2  H2O
The steps to balancing:
Step 1. Count the number of moles of
atoms of each element on both
product and reactant sides
Reactants
Products
2 mol H
2 mol O
2 mol H
1 mol O
Step 2. Determine which elements are not
balanced – Oxygen is not balanced
Step 3. Balance one element at a time by
changing the coefficients
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H2 + O2  2H2O
This balances oxygen, but is hydrogen still
balanced?
2H2 + O2  2H2O
Step 4. Make sure the law of conservation of
mass is obeyed
Reactants
Products
4 mol H
4 mol H
2 mol O
2 mol O
Balance the following equations:
1. C2H2 + O2  CO2 + H2O
2. AgNO3 + FeCl3  Fe(NO3)3 + AgCl
3. C2H6 + O2  CO2 + H2O
4. N2 + H2  NH3
Balance the following equations:
1. 2C2H2 + 5O2  4CO2 + 2H2O
2. 3AgNO3 + FeCl3  Fe(NO3)3 + 3AgCl
3. 2C2H6 + 5O2  4CO2 + 6H2O
4. N2 + 3H2  2NH3
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Synthesis reactions
The joining of two or more elements or
compounds, producing a product of different
composition
A + B  AB
Examples:
 metal + nonmetal  salt: 2Na(s) + Cl2(g) 
2NaCl(s)
 H + Cl  HCl
 MgO(s) + CO2(g)  MgCO3(s)
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Produce two or more products from a single
reactant
Reverse of a combination reaction
AB  A + B
Examples:
 2HgO(s)  2Hg(l) + O2(g)
 CaCO3(s)  CaO(s) + CO2(g)
 Removal of water from a hydrated material
Single-replacement
• One atom replaces another in the
compound producing a new
compound
A + BC  B + AC
Examples:
•
Cu(s)+2AgNO3(aq)  2Ag(s)+Cu(NO3)2(aq)
•
2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g)
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Activity Series – lists metals in order of
decreasing reactivity (p.333)
Reactive metals will replace any metal listed
below it in the activity series
If the metal is below, no reaction occurs
Halogen(7A) can replace other halogens that
are below it in the periodic table
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2K(s) + 2H2O(l) 
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Zn(s) + Cu(NO3)2(aq) 
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Cu(s) + Al2O3(aq) 
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Br2(aq) + 2NaI(aq) 
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Br2(aq) + NaCl 
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2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
Zn(s) + Cu(NO3)2(aq)  Cu(s) +
Zn(NO3)2(aq)

Cu(s) + Al2O3(aq)  No reaction
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Br2(aq) + 2NaI(aq)  2NaBr(aq) + I2(aq)
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Br2(aq) + NaCl  No reaction
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Two compounds undergo a
“change of partners”
Two compounds react by
exchanging atoms to produce
two new compounds
AB + CD  AD + CB
Double-displacement reaction
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Exchange of positive ions
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Occur in aqueous solution
To occur:
1.
One of the products is slightly soluble and
a precipitates forms
2.
One product is a gas
3.
One of the products is a molecular
compound, like water
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Acid + base  water and salt
HCl(aq)+NaOH(aq) NaCl(aq)+H2O(l)
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Formation of solid lead chloride from lead
nitrate and sodium chloride
Pb(NO3)2(aq) + 2NaCl(aq)  PbCl2(s) +
2NaNO3(aq)
AB + CD  AD + CB
Chemical change in a solution that results in one
or more insoluble products
Solubility Rules (p.344)
1. salts of alkali metals and ammonia  soluble
2. nitrate salts and chlorate salts  soluble
3. sulfate salts, except compounds with Pb, Ag, Hg,
Ba, Sr, and Ca  soluble
4. Chloride salts, except with Ag, Pb, and Hg
soluble
5. carbonates, phosphates, chromates, sulfides,
and hydroxides  most are insoluble
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Predicting Whether Precipitation
Will Occur
• Recombine the ionic compounds to have
them exchange partners
• Examine the new compounds formed
and determine if any are insoluble
• Any insoluble salt will be the precipitate
Pb(NO3)2(aq) + NaCl(aq) 
PbCl2 (s)
(?) + NaNO3 ((aq)
?)
Predict Whether These Reactions Form
Precipitates
 Potassium chloride and silver nitrate
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Potassium acetate and silver nitrate
Predict Whether These Reactions Form
Precipitates
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Potassium chloride and silver nitrate
KCl(aq) + AgNO3(aq)  KNO3(aq) + AgCl (s)
Potassium acetate and silver nitrate
KC2H3O2 + AgNO3(aq)  KNO3(aq) +
AgC2H3O2(s)
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Reactions with oxygen generally release
energy in the form of light or heat
Combustion
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Reactants: Oxygen and a hydrocarbons
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Products: CO2 and H2O
◦ Combustion of natural gas
 CH4+2O2CO2+2H2O
• Rusting or corrosion of iron
 4Fe + 3O2  2Fe2O3