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Supplemental packet page 117
This is a chemical recipe for
the decomposition of water
by electrolysis.
reactants
products
What did John Dalton in 1808 have to say about chemical reactions?
1. Chemical reactions involve just the simple rearrangement of atoms.
2. Atoms are conserved in a chemical reaction.
In other words, atoms are not created nor destroyed in chemical reaction.
Write the following opposite supplemental packet page 106
Is this true for the decomposition of water by electrolysis?
2 H2O
2 H2
+
1 O2
1. Chemical reactions involve just the simple rearrangement of atoms.
2. Atoms are conserved in a chemical reaction.
In other words, atoms are not created nor destroyed in chemical reaction.
Let’s see if John Dalton had assumed correctly.
This ture for the below decomposition of water by electrolysis.
2 H2O
O
H
H
2 H2
+
1 O2
H H
O
H H
O
O
H
H
4 hydrogen atoms
2 oxygen atoms
4 hydrogen atoms
2 oxygen atoms
Stoichiometry supplemental packet page 117
by balanced reaction
2 H2O
2 H2
+
2 molecule
2 molecules
1 O2
1 molecule
multiply through by
A number
2 x A number
2 x A number
1 x A number
A number equalsAvogadro's #
2 x 6.02x10
+23
2 x 6.02x10
+23
1 x 6.02x10
+23
Avogadro's # equals 1 mole
2 x 1 mole
2 x 1 mole
1 x 1 mole
count by weighing
2 x 18 grams
H2O
per
1 mole
H2O
2 x 2 grams
H2
per
1 mole
H2
1 x 32 grams
O2
per
1 mole
O2
36 grams H2O produces 4 grams H2 and 32 grams O2
by balanced reaction
2 H2O
2 H2
+
2 molecule
2 molecules
1 O2
1 molecule
multiply through by
A number
2 x A number
2 x A number
1 x A number
A number equalsAvogadro's #
2 x 6.02x10
+23
2 x 6.02x10
+23
1 x 6.02x10
+23
Avogadro's # equals 1 mole
2 x 1 mole
2 x 1 mole
1 x 1 mole
count by weighing
2 x 18 grams
H2O
per
1 mole
H2O
2 x 2 grams
H2
per
1 mole
H2
1 x 32 grams
O2
per
1 mole
O2
Stoichiometry supplemental packet page 118
Electrolysis
Dr.Gergens - SD Mesa College
O
H
O
H
H
H H
9 volt
battery
H
(source of electrons)
#
#

O
9 volt
battery
O
H
H
H
H
H H
O
O
2 H2O(l)
0
2(g)
2 H
+
0
1 O2(g)
Reduction is Gain, RIG
2H+

9 volt
battery
+ 2e
-
H20
The battery supplies those electrons
Remember hydrogen ions’s favorite charge in
its combined state is:
H+
2 H2O2-(l)
0
2(g)
2 H
+
0
1 O2(g)
Then what happened the oxygen atom in water?
Oxidation is loss of electrons, OIL
So oxide ion must have lost electrons

9 volt
battery
O2-
O0
+ 2e
-
Lost electrons in the electrolysis are attracted
To the positive ca hode
Remember oxygen ion’s favorite charge in
its combined state is:
O2-
2 H2O(l)
0
2(g)
2 H
+
0
1 O2(g)
REDOX,
is about the exchange of electrons.
Summary:
Reduction is Gain, RIG
2H+
Oxidation is Loss, OIL
O2-
+ 2e
-
H20
0
O + 2e
Take the summation of both half-reactions affords the overall rxn below
1 H2O
1 H2
+
1 O2
2
Supplemental packet page 106
Equilibrium
off-balanced
(unequal)
reactant to product
gas
formation
Equilibrium
balance
Precipitation
saturation
(solid formation)
Up & Down
Reflux
like
acid reflux
(heart burn)
Supplemental packet page 106
T he chemical equation is the short hand notation for a chemical reaction.
Reactants
react to pr oduce
Products
Law of Conservation of M ass - Matt er cannot be gained or lost in t he process of a chemical
reaction. T he law of conservat ion of mass states t hat we must have a balanced equat ion.
List five factors involved in the const ruct ion of an equation or "chem ical recipe."
1.
T he identit y of product s and reactants must be specified.
2.
React ant s are writt en to t he left of t he react ion arrow (---->) and product s to t he right .
3.
T he physical st at e of react ant s and product s is shown is parent heses;
(s), (l), (g), (aq).
Recall (aq) means aquesous solut oins (solute + solvent )
4.
T he sym bol over the reaction arrow means that heat energy is necessary for t he react ion t o occur.
5.
T he equation must be balanced.
Supplemental packet page 106
Steps for balancing a chemical equation
Step 1:
Step 2:
Step 3:
Step 4:
Note:
Count t he number of atoms of each element on bot h the product and react ant side.
Determ ine which atoms are not balanced.
Balance one atom at a t ime, using coefficient s. St art wit h atoms t hat appear
only once in t he react ant s and only once in t he products. Usually leave
Hydrogen at om s followed by Oxygen atoms until last .
After you believe t hat you have successfully balanced t he equat ion, repeat Step
1, to be certain that mass conservation has been achieved.
DO NOT Change subscri pts i n a mol ecul ar formul a ( i.e., 2 NaCl
Na2 Cl2 )
X
Don’t do this!!!!
Write this into our notes
22 Mg
+
11
O2
22 MgO
In balancing, we would like the lowest whole number molar ratio.
Where the number out in front is called a molar coefficient.
2 Mg
+
1 O2
2 MgO
But what if an individual balanced the magnesium first?
2 •21
Mg
+
1
1
2
O2
21 MgO
The reaction is balanced, BUT there is a fractional molar coefficient.
We must remove the fraction by multiplying through by 2.
2• 1
2
2•1
22 Mg
+
11
2•1
O2
22
MgO
In my opinion, the following is the easiest way to balance, if you :
1) always balance oxygens last;
2) then multiply by factor of 2, to remove any fractional
molar coefficient that might be present in the balanced reaction.
2 •22 Fe
+ 33 O2
22
2• 3
2
2•2
24 Fe
+ 3 3 O2
2
11 Fe2O3
2•1
12 Fe2O3
Note: We are going for the lowest whole number
Molar coefficient ratio
Finally, name the compounds and give physical states.
2 Mg
(s)
magnesium metal
solid
+
1 O2
(g)
oxygen
gas
24 Fe(s) + 33 O2 (g)
2
iron metal
solid
oxygen
gas
2 MgO
(s)
magnesium oxide
solid ionic salt
12 Fe2O3(s)
iron (III) oxide
solid TM ionic salt
Combustion of methane gas
1CH
1
?2 2
4 + 2O
Always balance oxygens last
? • O2 = 4
1 2 + 2H
1CO
2 2O
1 • O2 + 2 • 1O
2
+
2 =4
Combustion of ethane gas
7
2 1C
1 2H6 + ?7 O2
22
Always balance oxygens last
2•1
2 • ?7• O2 = 7
2
2 2H6 + 7
1C
7 O2
2
2CO
2 2 + 3H
3 2O
2 • O2 + 3 • 1O
2•2 4
2+ • 3 3 = 7
2CO
4
2 + 63H2O
Combustion of methanol liquid
3
1CH
O
+
1
?3O2
4
2
1 2 + 2H
1CO
2 2O
Always balance oxygens last
1•O
+ ? • O2 = 4
1
+ ?• 2 =4
-1
-1
?• 2 =3
2
2
?
3
=
2
1 • O2 +
2
+
2 • 1O
2 =4
Now solve for “?”
Substract one from each side
Divide each side by 2
Combustion of methanol liquid
21CH
1
4O
+ 3?23O2
2x1
2x3
2
2
1CH
3 2
4O + 2O
1 2 + 2H
1CO
2 2O
2x1
2x2
4 2O
1CO
2
2 + 2H
Now balance the combustion of glucose (blood sugar)
11C6H12O6
+ ?66O2
6CO
6 2 + 66H2O
1 • O2 + 6 • 1O
12 + 6 = 18
+ ? • O2 = 18
Always balance oxygens last
1•O6
6
-6
+ ? • 2 = 18
-6
? • 2 = 12
2
2
?
= 6
Now solve for “?”
Substract 6 from each side
Divide each side by 2
Combination - Synthesis - PHOTOSYNTHESIS
6
CO2
+
6
H2Ochlorophyll
catalyst
1
C6H12O6
+
6 O2
Combustion
Don’t
leave as
of amethanol,
fraction, multiply
CH4O through by 2
combustion
3
2x 1 CH O +
1 CO
O2
4
2
2
2 CH O +
2 CO
3O
+
2H
2
+
4H
2
CO2
+
3
Combustion of formaldehyde, CH2O
1 CH O +
O 2–1
1O
C 4+
CO
2
__
4
2
2O
2O
Combustion of ethanol, C2H4O
1
C2H6O +
2
3
O2
2
What reactant was oxidized?
H2O
O 2– + 1 H2O
What reactant was reduced?
Ionic salt transfer reactions in aqueous solution
A+B- (aq) + C+D- (aq)
AD(?) + BC(?)
Ionic salt solubility in water
All group I salts soluble, Li,Na,K
All nitrate salts soluble
All ammonium salts soluble,NH4+
Driving forces for ion transfer,
a force that makes the reaction go.
Physical state formations:
If a solid forms
If a liquid forms
If a gas forms
you’ll need to determine state
based on some rules
Evidence for chemical change, ∆
Color change (tricky)
Heat evolved (tricky)
precipitation saturation (solids)
If a liquid forms (heat evolved)
If a gas forms (bubbles, odor)
Ionic salt transfer reactions in aqueous solution
A+B- (aq) + C+D- (aq)
AD(?) + BC(?)
Common sense tells us to mix ionic solutions in order to have an
reaction to occur. (we are not going to mix for the sake of mixing)
Use of common sense tells us that,
An acids mixed with a base (antacid) causes a neutralization.
H+A- (aq) + M+OH- (aq)
H2O (l) + MA(?)
Use of common sense tells us that,
An acids mixed with carbonate (HCO3-) produces CO2 water and salt
H+A- (aq) + NaHCO3 (aq)
H2O(l) + NaA(aq)
CO2 (g)
A+B- (aq) + C+D- (aq)
AD(?) + BC(?)
Now write the ions associated with each substance
Say
product
names
silver (I) nitrate + sodium chloride
silver
(I)the
cloride
+ sodium
nitrate
silver (I) nitrate + sodium chloride
Ag+ (NO3)– Na+ Cl-
silver (I) chloride + sodium nitrate
Ag+
Cl-
Na+ (NO3)–
Now write formuals for the products
Identify physical state in aqueous solution
Solubility rules need to be applied.
AgCl
(s)
+
NaNO3
(aq)
Xcharges
carbide ion phosphide ion phosphate ion
nitride ion sulfide ion
sulfate ion
oxide ion chloride ion
perchlorate ion
fluoride
borate ion
carbonate ion
nitrate ion
Combination - Synthesis (the REDOX process defined)
iron metal plus chlorine gas forms> iron (II) chloride
1
Fe(s)
+ 1Cl2(g)
1
FeCl2 (s)
Fe 2+
Analyzing the half reactions
1
Fe
o
Cl2
o
1
+ 2e-
Cl –
Cl –
Fe 2+ + 2e-
Oxidation
OIL
2Cl –
Reduction
RIG
Combination - Synthesis (the REDOX process defined)
iron metal
1
Fe(s)
chlorine gas forms iron (II) chloride
+ 1Cl2(g)
1
FeCl2 (s)
Fe 2+
Analyzing the half reactions
1
1
Fe
o
Cl2
o
1
+ 2e-
Cl –
Cl –
Fe 2+ + 2e-
Oxidation
OIL
2Cl –
Reduction
RIG
half
reactions
thecombining
electrons both
on the
reactant
side cancel the electrons on the product side
1 Fe(s)
+ 1 Cl2(g)
1 FeCl2 (s)
What reactant was oxidized?
2 Mg
Mg O
(s)
What reactant was reduced?
Mgo lost electrons
O2O
magnesium metal
solid
+
1 O2
(g)
oxygen
gas
Oxygen gained electrons
Mg MgO
2
O
2+
2–
(s)
magnesium oxide
solid ionic salt
What reactant was oxidized?
What reactant was reduced?
Fe
3+
O 2–
O 2–
Fe
O
O2
O
24 Fe(s) + 33 O2 (g)
2
iron metal
solid
oxygen
gas
Oxygen gained electrons
Fe 3+
O 2–
12 Fe2O3(s)
iron (III) oxide
solid TM ionic salt
Combustion of methanol in PLASTIC BOTTLE
REDOX MID-TERM
1
Fe
+
2 H2O
O
H
H
1
Cl2
1
2 H2
FeCl2
+
1 O2
H H
O
H H
O
O
H
H
4 hydrogen atoms
2 oxygen atoms
4 hydrogen atoms
2 oxygen atoms
BATTERY DEMO
SOLUBILITY in aqueous solutions