Download Chemistry 3 a Big Picture PPT File

Hard or Soft
Combustion
Ammonia
Energy level
diagrams
Analysing
substances
Endothermic and exothermic reactions
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Step 1: Energy must be
SUPPLIED to break bonds:
Step 2: Energy is RELEASED
when new bonds are made:
A reaction is EXOTHERMIC if more energy is RELEASED
then SUPPLIED. If more energy is SUPPLIED then is
RELEASED then the reaction is ENDOTHERMIC
Energy level diagrams
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Energy
level
Activation
energy
Using a catalyst
might lower the
activation energy
Energy given
out by
reaction
Reaction progress
Exothermic vs endothermic:
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EXOTHERMIC – more
energy is given out than is
taken in (e.g. burning,
respiration)
ENDOTHERMIC –
energy is taken in but
not necessarily given out
(e.g. photosynthesis)
Burning Methane
CH4 + 2O2
To burn methane
you have to break
all of these bonds:
And then you
have to make
these ones:
2H2O + CO2
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Burning Methane
CH4 + 2O2
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2H2O + CO2
Methane
Oxygen
Carbon dioxide
Water
Bond energies
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C-H = 435 Kj
O=O = 497 Kj
Total for breaking bonds = 4x435 + 2x497 = 2734 KJ/mol
C=O = 803 Kj
H-O = 464 Kj
Total for making bonds = 2x803 + 4x464 = 3462 KJ/mol
Total energy change = 2734-3462 = -728 KJ/mol
Drawing this on an energy diagram:
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2734 Kj
3462 Kj
-728 Kj
More energy is given out (3462) than is given in (2734) –
the reaction is EXOTHERMIC. The total (“nett”) energy
change is –728 Kj. An endothermic reaction would have a
positive energy change.
Bond energy values
C-H = 435 KJ/mol
O-H = 464 KJ/mol
O=O = 497 KJ/mol
C=O = 803 KJ/mol
C-O = 360 KJ/mol
C-C = 346 KJ/mol
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Burning Methanol
2CH3OH + 3O2
Total for breaking bonds = 6x435
(C-H) + 2x360 (C-O) + 2x464 (O-H)
+ 3x497 (O=O) = 5749 KJ/mol
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2CO2 + 4H2O
Total for making bonds =
4x803 (C=O) + 8x464 (O-H) =
6924 KJ/mol
Energy change = 5749-6924 (divide this by two as we are
dealing with two molecules of methanol) = -587.5 KJ/mol
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Reversible Reactions
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Some chemical reactions are reversible. In other words, they
can go in either direction:
A + B
e.g. Ammonium chloride
NH4Cl
C + D
Ammonia + hydrogen chloride
NH3 + HCl
If a reaction is EXOTHERMIC in one direction
what must it be in the opposite direction?
For example, consider copper sulphate:
Hydrated copper
sulphate (blue)
+ Heat
CuSO4.5H2O
Anhydrous copper
sulphate (white)
CuSO4 + H2O
+
Water
Reversible Reactions
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When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants
are added or taken away) an EQUILIBRIUM is achieved – in other words,
the reaction goes at the same rate in both directions:
A + B
Endothermic reactions
Increased temperature:
A + B
C + D
C + D
Exothermic reactions
Increased temperature:
A + B
C + D
More products
Less products
Decreased temperature:
Decreased temperature:
A + B
C + D
Less products
A + B
C + D
More products
Making Ammonia
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Guten Tag. My name is Fritz Haber and I won the Nobel
Prize for chemistry. I am going to tell you how to use a
reversible reaction to produce ammonia, a very important
chemical. This is called the Haber Process.
Nitrogen + hydrogen
Ammonia
N2 + 3H2
2NH3
Fritz Haber,
1868-1934
To produce ammonia from nitrogen and hydrogen you
have to use three conditions:
Nitrogen
Hydrogen
•High pressure
•450O C
•Iron catalyst
Mixture of NH3, H2 and
N2. This is cooled
causing NH3 to liquefy.
Recycled H2 and N2
Uses of Ammonia
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Ammonia is a very important chemical as it can be
used to make plant fertilisers and nitric acid:
Ammonia gas
Oxygen
Hot
platinum
catalyst
Nitrogen
monoxide
Cooled
Nitrogen
monoxide
Water and
oxygen
Nitric
acid
More ammonia can then be used to neutralise the nitric acid to
produce AMMONIUM NITRATE (a fertiliser rich in nitrogen).
Ammonia + nitric acid
NH3 + HNO3
Ammonium nitrate
NH4NO3
The trouble with nitrogen based fertilisers is that they can also create
problems – they could contaminate our drinking water.
Haber Process: The economics
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A while ago we looked at reversible reactions:
Endothermic, increased temperature
A + B
Endothermic
C + D
Exothermic, increase temperature
A + B
Nitrogen + hydrogen
Ammonia
N2 + 3H2
2NH3
C + D
Exothermic
1) If temperature was DECREASED the amount of ammonia formed would
__________...
2) However, if temperature was INCREASED the rate of reaction in both
directions would ________ causing the ammonia to form faster
3) If pressure was INCREASED the amount of ammonia formed would
INCREASE because there are less molecules on the right hand side of
the equation
Haber Process Summary
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A low temperature increases the yield of ammonia but is
too slow
A high temperature improves the rate of reaction but
decreases the yield too much
A high pressure increases the yield of ammonia but costs a lot
of money
To compromise all of these factors, these conditions are used:
Nitrogen
Hydrogen
•200 atm pressure
•450O C
•Iron catalyst
Mixture of NH3, H2
and N2. This is
cooled causing NH3
to liquefy.
Recycled H2 and N2
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Periodic table timeline
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Mendeleev and the periodic table
Mendeleev created the first modern periodic table by
grouping together elements with similar properties.
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Arranging elements into columns
When elements are arranged according to their properties
what patterns do you see?
hydrogen
is a special
case
H
He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K
reactive metals
reactive gases
unreactive gases
Similar elements go into the same columns.
Hydrogen is an exception – it is best positioned above the
reactive metals.
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The periodic table
Arranging all the elements by their atomic number and their
properties led to the creation of…
H
…the periodic table
He
Li Be
B C N O F Ne
Na Mg
Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ?
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Patterns: reactivity of metals
What happens to the reactivity of metals along a period?
What happens to the reactivity of metals down a group?
increase in reactivity
Which is the most reactive metal?
Li Be
Na Mg
Al
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg
increase in reactivity
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Patterns: reactivity of non-metals
Group 0 elements are the most unreactive of all elements.
For the remaining non-metals and metalloids, reactivity
increases up a group and along a period from left to right.
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increase in reactivity
Which is the
most reactive
non-metal/
metalloid?
increase in reactivity
He
B C N O F Ne
Si P S Cl Ar unreactive
Ge As Se Br Kr
Sb Te I Xe
At Rn
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Patterns, atomic number and electrons
The periodic table shows that patterns in the properties of
elements are linked to atomic number.
H
Li Be
Na Mg
What links atomic number and
the properties of elements?
electrons
He
B C N O F Ne
Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg ? ? ? ? ? ? ?
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Atomic number and electrons
The properties of elements are hugely influenced by the
number and arrangement of electrons in the atom.
What links atomic number and the number of electrons in
an atom?
atomic number = number of protons
number of protons = number of electrons
atomic number = number of electrons
As atomic number increases by one, the number of electrons
also increases by one.
This means that the elements in the periodic table are also
arranged in order of the number of electrons.
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Electron shells
Electrons are arranged in shells around an atom’s nucleus.
Each shell has a maximum number of electrons that it can
hold. Electrons will fill the shells nearest the nucleus first.
1st shell holds
a maximum of
2 electrons
2nd shell holds
a maximum of
8 electrons
3rd shell holds
a maximum of
8 electrons
This electron arrangement is written as 2,8,8.
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Electrons in period 1
Elements in period 1 only have electrons in the first shell.
Why are there only two elements in period 1?
1
1
2
3
4
5
6
7
0
H
He
1
2
The first shell can only hold a maximum of two electrons,
so period 1 only includes the elements hydrogen and helium.
What is special about the outer shell of helium?
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Electrons in period 2
Elements in period 2 all have a complete first shell.
What happens to electrons in the second shell in period 2?
2
1
2
3
4
5
6
7
0
Li
Be
B
C
N
O
F
Ne
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8
The second shell is completed one electron at a time going
across the period from left to right.
What is special about the outer shell of neon?
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Electrons in period 3
Elements in period 3 have complete first and second shells.
What happens to electrons in the third shell in period 3?
1
3
2
Na Mg
3
4
5
6
7
0
Al
Si
P
S
Cl
Ar
2,8,4
2,8,5
2,8,6
2,8,7
2,8,8
2,8,1 2,8,2 2,8,3
The third shell is completed one electron at a time going
across the period from left to right.
What is special about the outer shell of argon?
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Patterns of electron arrangements
Consider the electron arrangements of the first 20 elements
in the periodic table.
1
2
3
4
5
6
7
0
2
1
1
2
2,1
2,2
2,3
2,4
2,5
2,6
2,7
3
2,8,1
2,8,2
2,8,3
2,8,4
2,8,5
2,8,6
2,8,7 2,8,8
4
2,8,8,1 2,8,8,2
2,8
What is the pattern of outer shell electrons in a group?
What is the pattern of outer shell electrons across a period?
What is the pattern of full electron shells in a group?
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Electron trends in the periodic table
Trends down a group:
 the number of outer shell electrons is the same;
 the number of complete electron shells increases by one.
The number of a group is the same as the number of
electrons in the outer shell of elements in that group,
except for group 0.
Trends across a period:
 the number of outer shell electrons increases by one;
 the number of complete electron shells stays the same.
The point at which a new period starts is the point at which
electrons begin to fill a new shell.
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What’s the electron arrangement?
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Names of groups in the periodic table
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Glossary
 atomic number – The number of protons in an atom.






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Sometimes called the proton number.
electron arrangement – A shorthand way of writing the
number of electrons in an atom’s electron shells.
element – A substance made up of only one type of atom.
group – A column in the periodic table containing elements
with the same number of outer shell electrons and similar
chemical properties.
period – A row in the periodic table containing elements
with the same number of full electron shells.
periodic table – The table that lists all the elements in
order of increasing atomic number, arranged into groups and
periods.
property – Any characteristic of an element.
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Alcohols
Alcohols are a group of organic
molecules which contain oxygen.
They form a HOMOLOGOUS
series.
Naming the Alcohols
The names of alcohols follow the same
pattern as the alkanes and alkenes.
The first part of the name relates to
the number of carbons in the chain.
The second part of the name is -anol
1 carbon
Butanol.
2 carbons
Methanol
3 carbons
Pentanol
4 carbons
Ethanol
5 carbons
Propanol
Alkanes
Alkenes
Alcohols
CnH2n+2
CnH2n
CnH2n+1OH
C2H4
C3H6
C4H8
C5H10
CH3OH
C2H5OH
C3H7OH
C4H9OH
C5H11OH
CH4
C2H6
C3H8
C4H10
C5H12
Formula of Alcohols
All alcohols have the formula;
CnH2n+1OH
Methanol
Ethanol
Propanol
CH3OH
C2H5OH
C3H7OH
Structure of Alcohols
C – 4 bonds
H – 1 bond
O – 2 bonds
(must be between a C and an H)
Methanol
H
H
C O H
H
H
H
H
C
C
H H
Ethanol
O
H
Properties of Alcohols
• They are FLAMMABLE/NOT FLAMMABLE
• Their density (heaviness)
INCREASES/DECREASES as the number
of carbons increases
• SOME/ALL of them are poisonous
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Alcohols:
■ dissolve in water to form a neutral solution
■ react with sodium to produce hydrogen
■ burn in air
■ are used as a fuels and solvents, and
ethanol is the main alcohol in alcoholic
drinks
Carboxylic Acids
Carboxylic Acids
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
51
Carboxylic Acids
Ethanol can be oxidised to ethanoic
acid, either by
chemical oxidising agents or by
microbial action.
Ethanoic acid is the main acid in
vinegar.
52
Carboxylic Acids
A carboxylic acid
• Contains a carboxyl group, which is a
carbonyl group (C=O) attached to a
hydroxyl group (—OH).
• Has the carboxyl group on carbon 1.
O

CH3 — C—OH
or
CH3COOH
53
Models of Carboxylic Acids
• The three-dimensional models show
the geometry of atoms in carboxylic
acid molecules.
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
54
Common Carboxylic Acids
Methanoic acid (formic acid)
O
║
H ─ C─ OH
ethanoic acid (acetic acid)
O
║
CH3─ C ─ OH
Draw propanoic acid!
55
Acidity of Carboxylic Acids
Carboxylic acids
• dissolve in water to produce acidic solutions
• ■ react with carbonates to produce carbon
dioxide
• ■ do not ionise completely when dissolved in
• water and so are weak acids
• ■ aqueous solutions of weak acids have a
higher pH value than aqueous solutions of
strong acids with the same concentration
56
Esters
Esters and Naming Esters
Carbolic acids react with alcohols in the
presence of an acid
catalyst to produce esters
57
Esters
In an ester,
• The H in the carboxyl group is
replaced
with an alkyl group.
O

CH3 — C—O—CH3
ester group
58
Esterification is
• The reaction of a carboxylic acid and
alcohol in the presence of an acid catalyst
to produce an ester.
O

CH3—C—OH + H—O—CH2—CH3
O

CH3—C—O—CH2—CH3 + H2O
ethyl ethanoate
(an ester)
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The Water Cycle
Water
Water Treatment
Made safe to drink by removing
solids and micro-organisms
Water source  Filter solids
Sedimentation of small particles using
Aluminium sulphate
Filter of fine sand
Chlorine  used to disinfect
Distillation =
PURE WATER
Carbon  reduces Cl levels
Ion exchange resin
Silver  discourage bacterial
growth on filter
Ca2+
hard water
Mg2+
Ca2+
Mg2+
soft water
lather
hard water
SCUM
Ions not
removed by
water
purification
Ca2+
Mg2+
Ca2+
Stearate
Mg2+
Calcium ions from water + Stearate ions from soap
(Soluble)
(Soluble)
Calcium Stearate
(Insoluble)
SCUM
Types of hard water Temporarily Hard
Co2
Limestone
Ca2+
Soluble Calcium Hydrogencarbonate
CaCO3(s) + CO2(g) + H2O(l)
Ca(HCO3)2(aq)
Ca(HCO3)2
Heat
Scum
Ca(HCO3)2(aq)
CaCO3(s) + CO2(g) + H2O(l)
Limescale
Types of hard water Permanently Hard
Gypsum
Anhydrite
Calcium Sulphate
Heat
Cannot be
softened by
heating
CaSO4(aq)
Removing hardness from water
Ca2+
Mg2+
Na2CO3
Sodium Carbonate
Calcium ions + Sodium Carbonate
Sodium ions + Calcium Carbonate
Install a water softener
Ion exchange column
contains resins
Ca2+
Mg2+
Exchanged
for
Na+
Install a water softener
Na+
Water
Hard Water
Soft water  easy lather
Hard water  less lather
Contains Mg2+ and Ca2+ ions, dissolved
when water passes through rocks
SCUM
When hard water
reacts with soap.
SCALE
When hard water
is heated.
SCALE is basically limescale which is Calcium
Carbonate which is a solid ppt and forms on
metal appliances reducing efficiency.
+ve
- Ca for
bones/teeth
-ve
- Kettles furrow up
 less efficient
Water
Removing Hard Water
Use
washing
soda
Add Sodium Carbonate
Precipitates out the Ca and
Mg ions to form insoluble
carbonates
Ion
Exchange
(water
softener)
Filled with resin.
Contain Sodium/Hydrogen Ions
As the water is passed through
the resin, the Na/H ions are
EXCHANGED with the Ca/Mg
ions.
Needs to be topped up with Na
ions so NaCl is poured in to
replenish.
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Flame colour
Lithium
Flame colour
Bright red
Flame colour
sodium
Flame colour
Yellow
Flame colour
potassium
Flame colour
lilac
Flame colour
calcium
Flame colour
Red
Flame colour
barium
Flame colour
green
Test for carbonates
Carbonates react with dilute acids to
form
Test for carbonates
Carbon dioxide,
carbon dioxide turns limewater milky
Precipitation with sodium
hydroxide
Aluminium, calcium and magnesium
ions form
Precipitation with sodium
hydroxide
white precipitates
Precipitation with sodium
hydroxide
Aluminium hydroxide precipitate
dissolves
Precipitation with sodium
hydroxide
in excess sodium hydroxide solution
Precipitation with sodium
hydroxide
Copper(II) ions form
Precipitation with sodium
hydroxide
blue precipitates
Precipitation with sodium
hydroxide
Iron (II) ions form
Precipitation with sodium
hydroxide
green precipitates
Precipitation with sodium
hydroxide
iron(III) ions form
Precipitation with sodium
hydroxide
Brown precipitates
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
Silver chloride is
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
White precipitate
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
Silver bromide is
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
Cream precipitate
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
Silver iodide is
Halide ions in solution produce
precipitates with silver nitrate
solution in the presence of dilute
nitric acid
Yellow precipitate
Test for sulfate ions
Sulfate ions in solution produce a
Test for sulfate ions
white precipitate with barium
chloride solution in the presence of
dilute hydrochloric acid
Test for ammonium ions
Ammonium ions react with sodium
hydroxide solution to form
ammonia.
Test for ammonium ions
Ammonia gas turns
Damp red litmus paper blue.
Test for nitrate ions
Nitrate ions are reduced by
aluminium powder in the presence of
sodium hydroxide solution to
Test for nitrate ions
form ammonia
Organic compounds
Organic compounds burn or char
when
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