Transcript Petroleum B Notes

Petroleum B
Petroleum as an energy source
Buried Sunshine
Fossil fuels - oil, coal, natural gas, are
all dead plants which grew be
photosynthesizing sunlight.
Therefore, fossil fuels are buried
sunlight.
There is no 100% conclusive evidence
of where petroleum comes from.
The process of making fossil fuels over
time happens too slow.
Potential vs. Kinetic Energy
Potential Energy is stored energy.
 Chemical energy is a kind of potential energy =
battery
Kinetic Energy is energy of
movement/motion
During a chemical reaction the potential
energy in compounds are released and the
products (usually) have less potential
energy than the reactants.
Bond breaking and bond making
In a chemical reaction, bonds must first be
broken.
 Combustion of methane
 CH4 + O2  CO2 + H2O
 The methane and oxygen molecules must first
be broken. This requires energy to be ADDED
= Endothermic
 Next, the bonds must reform, but in different
combinations. When this happens it is an
exothermic reaction = energy is released
Potential Energy DiagramExothermic Reaction
Potential Energy DiagramEndothermic Reaction
Bond breaking and bond
making
If the energy added (endothermic) is
greater than the energy given off
(exothermic), then the overall reaction
is ENDOTHERMIC.
If the energy added (endothermic) is
less than the energy given off
(exothermic), then the overall reaction
is EXOTHERMIC.
Bond breaking and bond
making
EXOTHERMIC = feels hot to the
touch
 energy was released to the
environment
ENDOTHERMIC = feels cold to the
touch
Energy was absorbed from the
environment
Energy Conversion
Consider the energy required to power
a hair dryer.
No matter how many times energy is
transformed to another energy it is
never “used up”.
Law of Conservation of Energy - energy
is never created or destroyed, it only
changes forms.
Energy Efficiency
Devices that convert chemical energy
(fossil fuels) to thermal energy (heat) then
to mechanical energy (movement) are less
than 50% efficient - this refers to the energy
made by power plants.
 Solar cells and fuel cells (for cars) are cleaner
and more efficient.
Some energy is always “lost” when it is
converted from one form to another.
Energy Efficiency
Low efficiency of the machine using
the energy.
The most efficient car engines are only
25% efficient. The rest of the energy is
lost as heat.
Do B.5 Energy Conversion Efficiency
Problems on p 245.
Combustion
BURNING!!
Burning a hydrocarbon will always yield
Carbon Dioxide (CO2) and Water (H2O)
Energy is always released - it feels hot.
C25H52 + O2  CO2 + H2O
combustion of candle wax.
Where does the energy come from?
 The chemical bonds release energy when they
are destroyed.
Specific Heat Capacity
Specific Heat Capacity - the amount of
heat needed to raise the temperature
of a substance by 1C.
Calculating Specific Heat
Capacity
Suppose a 10.0 g water sample is
heated from 25.0C to 30.0C. How
much energy must have been
added to the water?
210 J of heat
Heat of Combustion/Molar
Heat of Combustion
Heat of Combustion - the amount of heat
given off when an amount of a substance is
burned
 The “amount” is usually 1 gram.
 Measured in kJ/g
Molar heat of combustion - the amount of
heat given off when 1 mole of any
substance in burned.
 Measured in kJ/mol
Calculating Heat of
Combustion
How much energy (in
kilojoules) is released when
76.0 g of hectane is burned?
Calculating Molar heat of
combustion
How much energy (in kJ) is
released by completely
burning 25.0 mol hexane.
104000 kJ
Altering Fuels
There are only 9.9 gallons of gasoline
in a 55 gallon drum of crude oil after
fractional distillation.
Now, as much as 25.9 gallons (47%) of
gasoline can be taken from a 55 gal.
drum of crude oil because of altering
of molecules
Scientists can change existing molecules
to meet the demand.
Cracking
Cracking - process of converting large
hydrocarbon molecules to smaller
ones through the application of heat
(600C-700C) and catalysts.
Kerosene: 16 C’s to gasoline 8 C’s
Hydrocarbons up to about 14 C’s can be
produced through cracking.
Cracking
Catalysts are used to speed up existing
reactions but they themselves are not
used up.
Catalytic cracking is more efficient
because it requires less heat
Bonus: During cracking Methane,
ethane, propane, and butane made and
immediately burned to keep the temp.
hot.
Pinging/Knocking
“Gasoline” is composed mainly of straight
chained molecules of: hexane, heptane, and
octane.
 Gas-Air mixture is first compressed in the
cylinder (piston) just before it is ignited by the
spark plug.
 Sometimes the compressed gas explodes before
the spark plug ignites it.
 This causes the piston to bang back against the
crankshaft = pinging/knocking
 These burn to rapidly - to hot causing the
engine to “ping” or “knock.”
 Branched-chain alkanes burn more favorably
in car engines
This is the best “octane” - isooctane
Octane Rating
“Gasoline” is sold at varying grades.
Isooctane is assigned an octane
number of 100.
Straight-chained Heptane is assigned
an octane number of 0.
Heptane has very poor engine
performance.
Finding Octane Rating
Octane rating is determined under two
conditions:
A free-running engine
And engine pulling a load (towing)
The results of these two processes are
averaged together.
The higher the rating the more anti-knock
Refer to the following for more
information:
http://auto.howstuffworks.com/question90.
htm
Octane rating
Leaded Fuel: tetraethyl lead was
added to gasoline to increase octane
rating.
However, it added lead compounds to
environment.
Oxygenated Fuels
With lead-based fuel out, an
alternative had to be found.
Oxygenated fuels - a blend of
additives added to fuel to increase
the octane rating.
The molecules of the additives
contain oxygen as well as C and H.
Oxygenated Fuels
Oxygenated fuel provide LESS
energy per gallon = less miles per
gallon.
BUT, they increase octane number
(better performance of car) while
reducing exhaust pollutants, and
less emissions like CO.
Oxygenated Fuels
Methanol is a common oxygenated fuel
(CH3OH).
 An additive to fuel
 Boosts octane rating (better engine
performance).
 Methanol can be made from coal, natural gas,
wood, and corn
 Conserves nonrenewable resources
 Gasohol - blend of 10% ethanol, 90% gasoline
 Can be used without engine modifications
Oxygenated Fuels
 MTBE (methyl tertiary-butyl ether) was added to
gas in late 1970’s.
 Octane rating of 116 - pollution reducing
oxygenating chemical.
 However,late 1990’s: bad gas storage units
allowed MTBE to seep into groundwater.
Unpleasant taste to water; became a concern
even though no apparent health risk.
 MTBE since them has been phased out.
Oxygenating fuels
MTHE (methyltetrahydrofuran)
Octane rating = 87 same as gasoline
It can increase the level of oxygenated
fuel
Can be obtained from renewable
resources like papermill waste products.
Straight-chain to branched-chain
Straight-chained hydrocarbons burn too
hot.
Branched-chained hydrocarbons burn more
favorably.
Scientists can convert straight-chained to
branched-chained.
 The straight-chained vapor is heated with a
catalyst
 This is called isomerization.