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1 AIES

CHEMISTRY

15 November 2016

Stoichiometry
STOICHIOMETRY

Total mass of reactant = Total mass of product
EXAMPLE:
Equation
Ratio
Molar mass Mr
Mass(g)

~ 2H2 + O2 —> 4H2O
~ 2 : 1 :
4
~ 2 : 32 :
18
~ 2(2) : 1(32): 4(18)
4g : 32g : 36g

Mass of element
% of element in a compound = ————————————
Total mass of compound
EXAMPLE:
CH4 [Ar: C=12, H=1]
12
% C = ———— X 100 %
12+4(1)
= 75 %

4
% H =———— X 100 %
12+4(1)
= 25 %

Mass of pure product
The % purity of a product = ——————————— X 100 %
Mass of impure product

EXAMPLE:

X = 7
...

6
% Purity = ——
7
...
02 X1023
1 Mole of water molecules = 1
...
02 X1023

X Molar mass
————————>
Number of Moles

Mass (g)
<————————
÷ Molar mass

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1 AIES

CHEMISTRY

15 November 2016

Mass from equation:
EXAMPLE: what mass of oxygen combine with 64g of methane, how much carbon dioxide is
produced?
Chemical Equation
Mole Ratio

~ CH4 + 2O2 —> CO2 + 2H2O
~ 1 : 2
1 : 2
64 ÷ [12+4(1)]
Mole of known substance ~ 4
Using Ratio
~
8
4
8
X2(16) X[12+2(16)] X[2(1)+16]
Change to Molar mass
~
256
176
144
^
^
|
|
256 g of O2 176 g of CO2
Molar Volume:
Unit: dm3mol-1 OR cm3mol-1
Volume of gas
Number of mole of gas = ———————
24 dm3mol-1
EXAMPLE: Mole of 2 dm3mol-1 of chlorine gas
2 dm3
Number of mole of gas = ——————
24 dm3mol-1
= 0
...
What is its
Empirical Formula?

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1 AIES

CHEMISTRY

15 November 2016

EXAMPLE: 64 g of sulphur combine with 64 g of oxygen to form an oxide of sulphur
...
Molecular mass = 42
...
of surrounding Increase
EXAMPLE: Neutralisation
Reactive metal reacts with acid
Metal Displacement
Combustion
Freezing & Condensation

Endothermic Reaction
Heat Absorbed from surrounding
Temp
...
5H2O <—> CuSO4 + 5H2O
In a closed system, a reversible reaction will reach a state of dynamic equilibrium, where:
1
...
Reactions are still going on, all the time, in the
container
...
The forward and backward reactions are both going on at the same speed
...
Equilibrium means there is no overall change in the amount of reactants and products
...

Use catalyst to speed up both forward and backward reaction equally
Removing product, reaction form more product to restore balance
...
will increase yield but will slow down the reaction so
moderate temp
...

Catalyst speed up both forward and backward reaction equally so equilibrium is reached faster
Cooling the ammonia produced will remove it from the equation so reaction will keep trying to
restore the equilibrium by forming more ammonia
...

Anode: Impure Metal X
Cathode: Pure Metal X
Electrolyte: An aqueous solution contains ions of purifying metal [Metal X]
Aluminium Extraction
Bauxite —> Aluminium oxide—>Cryolite
950ºC—>Molten Aluminium oxide

Electrolysis
Same type of electrode (mostly)
Positive to Negative

Different
Type of Electrode
Energy Change

Required

Power Supply

Positive

Anode

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Voltaic Cell
Must be different type of metals
Negative to Positive
Do not required
Negative

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1 AIES

15 November 2016

CHEMISTRY

Negative

Cathode

Positive

Terminal of battery

Terminal

More reactive = -ve

Oxidation at Anode (loss of electrons), Reduction at the Cathode (gain of electrons)

Contact Process

Temp
...

Particles gain more kinetic energy
Particles collide more often
More successful collision between particles
Higher Pressure:
Increase number of successful collision between particles
Equilibrium shift to the side with less molecule

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