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Chapter 9
Energy and Hydrocarbons
Chapter Outline
Background & Energy from Fuels
Alkanes: Backbone of Organic Chemistry
Alkenes and Alkynes: Reactive cousins of Alkanes
Cyclic Hydrocarbons
Petroleum
Natural Gas
Coal
Methanol (Gasohol)
Define some terms
Energy is a common idea that ran through the first half
of the class.
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–
–
–
–
–
What is Energy?
What is Heat?
What is Temperature?
What is the difference between heat and temperature?
What are the ‘units’ of each measurement?
Exothermic vs. Endothermic
Energy
Energy is defined as ‘the capacity to do work’
– What does this mean to you?
Energy: Capacity to do work or to transfer heat!
Types of Energy
Kinetic Energy – Energy of Motion
Ek = ½ mv2
m= mass (kg)
v = velocity (m/s)
Ek = Joules
Potential Energy – Stored energy based on the
position of one object with respect to another
Ep = m *g* h
m = mass (kg)
g = gravitational constant
= 9.806 m/s2
h= distance above
reference
Example
What is the kinetic Energy of a bowling ball
moving at a velocity of 1.5 m/s? (Mass of
bowling ball = 7.5 kg)
Ek = ½ mv2
Units of Energy
Heat can have the following units
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–
–
–
–
–
–
–
Joules (J) = 1 kg*m2/s2
Kilojoules(kJ)
calories (cal) = 4.184 Joule
Kilocalories (kcal) = 1000 calories
Dietary Calories = Calories (Cal) = 1 kcal
Erg
BTU
Foot-pounds
Energy
Calculate the amount of potential energy of a 1 kg
book raised about 6 ft (~2 meters) into the air.
First Law of Thermodynamics
Energy is neither created nor destroyed.
– The Energy is said to be “transferred or
transformed”!
What happened to the energy of the book?
Heat vs. Temperature
Some of the energy was transformed to sound
energy and some converted to heat!
WHAT IS HEAT?
– Before we consider heat … let’s look at temperature!
Temperature
Think back to global warming
– vibrating molecules caused an increase in
temperature
Temperature – average kinetic energy of molecules
in a substance.
What is Heat?
Heat is the total amount of energy in a substance
– In other words – its the amount of thermal energy that a
system contains.
Heat Energy = (specific heat)*(amount of substance)*(Temperature)
What’s the difference between Heat and Temperature?
Think of this Example –
A drop of boiling water and 4 liters of boiling water. Which one has more energy?
What is a calorie?
Based on the work of James Joule (late 1800’s)
– One calorie = amount of heat required to raise 1
gram of water 1 degree Celsius.
– One calorie = 4.184 Joules
Units of Energy
Heat can have the following units
–
–
–
–
–
–
–
–
Joules (J) = 1 kg*m2/s2
Kilojoules(kJ)
calories (cal) = 4.184 Joule
Kilocalories (kcal) = 1000 calories
Dietary Calories = Calories (Cal) = 1 kcal
Erg
BTU
Foot-pounds
Some ‘exercises’
1. How many joules are in 425 Cal?
2. How much energy is required to raise 1 gram of
water 1oC?
3. How much energy is required to raise 1000
grams (1 kg) of water from room temperature
(25oC) to boiling (100oC) ?
Exothermic vs. Endothermic
Draw energy diagrams for the following
processes.
– Dissolving of Urea in water
– Dissolving of Ethanol in water
9.1 Energy from Fuels
Source of Energy used in the United States - 2000
Renewable
7%
Natural Gas
24%
Petroleum
38%
Coal
23%
Nuclear
8%
Most of our energy comes from Fossil Fuels
(Petroleum, Coal, Natural Gas)
Combustion of Natural Gas
Natural Gas is mostly Methane
Consider the complete combustion of methane
____ CH4 + ____ O2 -> ____ CO2 + ____ H2O
Methane
Oxygen
Carbon dioxide
Is Energy Produced? How much?
Water
What determines if Energy is released or
absorbed in a chemical reaction?
Bond Energies!!
BOND ENERGIES
H
C
N
O
S
F
Cl
Br
I
C=C
C=C
N=N
N=N
Single Bonds
H
C
N
432
411 346
386 305 167
459 358 201
363 272
565 485 283
428 327 313
362 285
295 213
-
602
835
418
942
O
S
F
142
190
218
201
201
226
284
255
217
-
155
249
249
278
Multiple Bonds
C=N 615
N=O 607
O=O 494
C=O 799
Cl
Br
I
240
216 190
208 175 149
C=O 1072
Bond Energies are given in kJ/mole