Transcript Chemical Reactions

Chemical Reactions
Types of Reactions
•
There are five types of chemical
reactions we will talk about:
1.
2.
3.
4.
5.
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Synthesis reactions
Decomposition reactions
Single displacement reactions
Double replacement reactions
Combustion reactions
You need to be able to identify the type
of reaction and predict the products
Steps to Writing Reactions
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Some steps for doing reactions
1.
2.
3.
Identify the type of reaction
Predict the products using the type of reaction
as a model
Balance the equation
Don’t forget about the diatomic elements! In a
compound, it can’t be a diatomic element
because it’s not an element anymore, it’s a
compound!
1. Synthesis reactions
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Synthesis reactions occur when two substances
(generally elements) combine and form a
compound.
reactant + reactant  1 product
Basically: A + B  AB
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Example: 2H2 + O2  2H2O
Example: C + O2  CO2
The key to recognizing a synthesis reaction is to look for only
one product!
Synthesis Reactions
Practice
Predict the products. Write and balance the
following synthesis reaction equations.
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Sodium metal reacts with chlorine gas
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Magnesium reacts with fluorine gas
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Aluminum reacts with oxygen gas
2. Decomposition Reactions
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Decomposition reactions occur when a
compound breaks up into the elements or to
simpler compounds
1 Reactant  Product + Product
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In general: AB  A + B
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Example: 2 H2O  2H2 + O2
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The key to recognizing decomposition reactions is
to look for only one reactant.
Decomposition Reactions
Practice
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Predict the products. Then, write and
balance the following decomposition
reaction equations:
Solid Lead (IV) oxide decomposes
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Solid Aluminum nitride decomposes
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Iron (III) chloride decomposes
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Practice
Identify the type of reaction for each of the
following synthesis or decomposition reactions,
and write the balanced equation:
Nitrogen and oxygen react to form nitrogen
monoxide.
Solid cobalt reacts with solid sulfur to form cobalt
(III)sulfide.
Solid nitrogen triiodide decomposes.
Single replacement reactions
She’s seeing another man!
3. Single Replacement Reactions
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•
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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 new element + new compound
A + BC  AC + B (if A is a metal) OR
A + BC  BA + C (if A is a nonmetal)
Key to recognizing single replacement reactions:
Look for a pure element on each side of the equation.
K + H20  KOH + H2
Single Replacement Reactions
Single Replacement Reactions
Write and balance the following single replacement
reaction equations:
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Zinc metal reacts with aqueous hydrochloric acid
(HCl)
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Bromine gas reacts with sodium iodide.
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Silver reacts with aqueous potassium nitrate.
Single Replacement Reactions
More practice
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Sodium chloride solid reacts with fluorine gas
Aluminum metal reacts with aqueous copper
(II) nitrate
4. Double Replacement Reactions
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Double Replacement Reactions occur
when a metal replaces a metal in a compound
and a nonmetal replaces a nonmetal in a
compound
Compound + compound 
new compound + new compound
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AB + CD  AD + CB
Double replacement reactions:
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Examples
AgNO3 + NaCl  AgCl + NaNO3
K2SO4 + Ba(NO3)2  KNO3 + BaSO4
The ions switch partners, like
in square dancing.
Practice
Predict the products. Balance the equation.
HCl(aq) + AgNO3(aq) 
CaCl2(aq) + Na3PO4(aq) 
Pb(NO3)2(aq) + BaCl2(aq) 
FeCl3(aq) + NaOH(aq) 
H2SO4(aq) + NaOH(aq) 
5. Combustion Reactions
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Combustion reactions occur
when a substance 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
2) Oxygen to burn it with
3) Something to ignite the
reaction (spark)
Combustion Reactions
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In general:
CxHy + O2  CO2 + H2O
Products in combustion of
hydrocarbons are ALWAYS
carbon dioxide and water.
(although incomplete burning
does cause some by-products
like carbon monoxide)
Combustion is used to heat
homes and run automobiles
(octane, as in gasoline, is C8H18)
Combustion
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Example
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C5H12 + 8 O2  5 CO2 + 6 H2O
Write the products and balance the
following combustion reaction:
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C10H22 + O2 
Mixed Practice
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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 
Redox
Reactions.
Reduction
Oxidation
GCSE
Oxidation: Reduction:
•Gain of oxygen
•Loss of oxygen
•Loss of electrons •Gain of electrons
Increase in
oxidation
number
Decrease in
oxidation
number
4 Experiments:
1.
2.
3.
4.
Burning magnesium
Copper in silver nitrate solution
Chlorine solution and potassium
iodide solution
Sodium in Water
•Word equation
•Balanced symbol equation
Oxidised –
gains oxygen
2Mg(s) + O2(g)  2MgO(s)
Must be a redox!
Oxidised – loss of e-
Mg 
2+
Mg
Put the
e- in.
Reduced – gain of e-
O +2e-  O2-
+2e-
Cu(s) + 2AgNO3(aq)  Cu(NO3 )2(aq) + 2Ag(s)
Complete
the halfOxidised?
equations
Reduced?
Oxidised – loss of e-
Reduced – gain of e-
Cu
Ag+ +e-


Cu2+ +2e-
Ag
H2(g) + ½ O2(g)  H2O(g)
Covalent!
Need a new
definition.
No H+ or OH-
GCSE
Oxidation: Reduction:
•Gain of oxygen
•Loss of oxygen
•Loss of electrons •Gain of electrons
Increase in
oxidation
number
Decrease in
oxidation
number
Redox
Reactions.
Reduction
Oxidation
Oxidation Numbers

The oxidation number of an atom in
an element is zero.
E.g. Mg in Mg, O in O2.
Oxidation Numbers
The oxidation
numbers of atoms
in a compound add
up to zero.
F
-1
O
-2
Oxidation state of
C in CO2?
H
+1
?–4=0
Cl
-1

? = +4
Put the +!
Oxidation Numbers

The oxidation
numbers of atoms
in a compound add
up to zero.
Oxidation state of
Mg in MgCl2?
+2
F
-1
O
-2
H
+1
Cl
-1
Oxidation Numbers

The oxidation
numbers of atoms
in a compound add
up to zero.
Oxidation state of
N in NH3?
-3
F
-1
O
-2
H
+1
Cl
-1
Oxidation Numbers

The oxidation
numbers of atoms
in an ion add up to
the charge on the
ion.
F
-1
O
-2
Oxidation state of
S in SO42-?
H
+1
? – 8 = -2
Cl
-1
? = +6
Oxidation Numbers

The oxidation
numbers of atoms
in an ion add up to
the charge on the
ion.
Oxidation state of
S in S2-?
-2
F
-1
O
-2
H
+1
Cl
-1
Oxidation Numbers

The oxidation
numbers of atoms
in an ion add up to
the charge on the
ion.
Oxidation state of
N in NH4+?
-3
F
-1
O
-2
H
+1
Cl
-1
H2(g) + ½ O2(g)  H2O(g)
Covalent!
Need a new
definition.
No H+ or OH-
GCSE
Oxidation: Reduction:
•Gain of oxygen
•Loss of oxygen
•Loss of electrons •Gain of electrons
Increase in
oxidation
number
Decrease in
oxidation
number
H2(g) + ½ O2(g)  H2O(g)
H
0
0
O
+1 -2
Covalent!
Need a new
definition.
No H+ or OH-
H2(g) + ½ O2(g)  H2O(g)
H
0
0
+1 -2
O
Oxidised?
H – increase
in oxidation
number
Reduced?
O – decrease
in oxidation
number