Chemistry in Context:
Chapter 4: Energy, Chemistry,
and Society
Practice Problems:
All Ch. 4 problems with the
blue codes or answers on Page
527-528.
Energy and Society
• Energy drives industrial and economic progress;
energy production and use correlates well with
gross national product, life expectancy, infant
mortality, and literacy.
• Energy use has increased in stages from the
earliest hominids to 2000 years ago (discovery
of fire and domestication of animals) to the
Industrial Revolution (use of coal) and to the
present day (petroleum refining).
Figure 4.4 on Page 144
Annual U. S. Energy Consumption
Fig. 4.4 on Page 155
(a) U.S.A.
(b) World
-More hydroelectric
power used in the
world than the U.S.
-Geothermal, wind,
and solar energy
sources are grouped
under the “Other”
category
Conservation of Energy
Fig. 4.2 on Page 153
• Energy is neither created nor destroyed
(First Law of Thermodynamics); it is
converted from one form to another.
• Energy of universe is constant.
• Sun is the ultimate MAJOR source.
• Fossil fuels store chemical energy that can
be converted to heat or electrical energy.
Definition of Energy
• Energy is defined as the capacity to do
work (W)
• W = applied force (f) x distance (d)
• Movement of an object over a
specified distance constitutes work.
• Kinetic energy refers to the energy of
a moving object.
Heat Energy
• Thermal energy or heat can be determined indirectly by
knowing the specific heat capacity (CH) of the object
heated and its temperature (T) that is characterized by the
average kinetic energy of atoms or molecules.
• Heat (kJ) = CH (kJ/g-°C) x mass (g) x ∆T (°C)
• Temperature is commonly measured in K or °C by
scientists but the °F is popular among meteorologist.
K = 273 + °C and °C = (°F-32)/1.8
• As heat is applied, atoms or molecules gain kinetic energy
and move further apart and eventually overcome the
intermolecular forces during melting and boiling.
Fig. 4.5 on Page 156
Schematic Drawing of
a Bomb Calorimeter
Units of Measurement for Energy
•
•
•
•
•
Measure of heat or thermal energy
1 kcal = 1000 calories
1 Calorie = 1 kcal (Cal ≠ cal)
Calorie = food or nutritional calorie
Other energy units are British Thermal
Units, ergs, & foot-pounds.
• Energy of fuels are usually expressed as
kJ/mole or kcal/mole.
Units of Measurement for Energy
• Joule and calories are the more common units
for energy
• 4.184 joule (J) = 1 calorie
• One calorie is the amount of heat needed to
raise the temperature of 1 gram of pure liquid
water by 1 °C
• Temperature is a property that determines the
direction of heat flow; heat flows from a
hotter to a colder body.
Combustion
• Chemical reaction of fuel with oxygen to
form products and energy.
• Potential energy of reactants > than that of
products
• CH4 + 2 O2 → CO2 + 2 H2O + Energy
• Heat of combustion refers to the amount of
heat given off when a substance is burned in
oxygen.
Chemical Reaction
• Atoms are rearranged in reactants to form
new products with different structures; this
involves the breaking and making of
chemical bonds
• Energy is needed to initiate a reaction
usually (spark plug, match).
• Two types of chemical reactions are
classified according to the energy levels of
products relative to reactants.
Exothermic Reaction
• Chemical or physical change that releases
heat.
• Energy required for bond breaking is
smaller than the energy released by bond
formation.
• Energy (products)<energy (reactants)
• Energy change (Eproducts-Ereactants) is
negative.
Figure 4.6 on Page 157
Heat of combustion is
negative for exothermic
reaction
Endothermic Reaction
• Chemical or physical change that absorbs
energy.
• Energy required for bond breaking is greater
than the energy released by bond formation.
• Energy (products)>energy (reactants)
• Energy change (Eproducts-Ereactants) is positive.
Bond Energy (BE)
• Amount of energy needed to break a specific
chemical bond
• Single < double < triple (BE trend)
• BE increases as the atomic number of the
bonded homonuclear atoms decreases for H,
C, N, and O.
• BE increases as the polarity of a bond
increases from iodine to fluorine in their
bonds to H, C, N, and S.
-Net energy
change is also
called heat or
enthalpy of
reaction (U
(UH)
-Bond breakage
requires energy
(+ve
(+ve or up)
-Bond formation
releases energy
(-ve or down)
Fig. 4.8 on
Page 161
Table 4.1 on Page 159
Activation Energy & Fuels
• Activation energy (AE) is the energy
needed to start a reaction.
• Slow reactions, higher AE, poor fuels.
• Fast reactions, low AE, explosions result,
poor fuels.
• Useful fuels, moderate reactions and AE.
Rate of Reaction
Figure 4.11 page 163
Solar Radiation as an Energy Source
• Plants captured sunlight via chlorophyll for
photosynthesis.
• Photosynthesis converts solar energy to
chemical energy in the form of lipids,
carbohydrates, proteins, and cellulose.
• Prehistoric photosynthesis also provided plant
matter that were turned into fossil fuels under
extreme heat and pressure below ocean floor
or sedimentary formation.
• Increase surface area, smaller
particles (e.g. fluidized-bed power
plant → less pollutants)
• Increase temperature to overcome
activation energy barrier
• Use a catalyst to lower AE via
alternate reaction pathways.
Photosynthesis
• Energy (hν) + 6 CO2 + 6 H2O →
C6H12O6 + 6 O2
• Energy = 2800 kJ per mole of C6H12O6
or 15.5 kJ/g of C6H12O6
• Photosynthesis is endothermic since it
requires solar energy.
• Provides food from crops as well as fuel
in the form of bioethanol, biodiesel, and
fossil fuels.
Properties of Coal
Respiration
• C6H12O6 + 6 O2 →
6 CO2 + 6 H2O + 2800 kJ
• Respiration is the reverse of
photosynthesis and is equivalent to
combustion reaction.
• Energy released sustains various
activities of our bodies.
Table 4.2 on Page 166
Ethanol
Petroleum
29.7
48
• Better fuel than wood with energy of 30 kJ/g
compared to 10-14 kJ/g).
• Mixture of compounds approximated by
C135H96O9NS
• Si, Na, Ca, Al, Ni, Cu, Zn, As, Pb, Hg.
• Anthracite and bituminous coal have more energy
than lignite due to the lower oxygen %.
• Coal reserves are 20-40 times that of petroleum;
coal gasification needed.
Disadvantages of Coal
• Underground mining is dangerous.
– 1900 – present day > 100,000 workers killed
in coal mines
– Cave-ins, fires, explosions, poisonous gases,
and respiratory diseases.
• Strip mining causes environmental damage in the
form of erosion.
• Coal is a dirty fuel and emits soot, SOx, NOx, and
CO2 (greenhouse gases).
• Coal cannot be pumped readily like petroleum
and gas.
Figure 4.12 on Page 168
Oil embargo
Figure 4.14 page 169
Petroleum
• Major energy source in US
• Petroleum can be more easily collected and
transported than coal.
• Energy content at 48 kJ/g is higher than that
of coal.
• Gasoline from petroleum is the fuel of
choice for automobile or internal
combustion engines.
• Low sulfur and other elements.
Refining Process
• Fractions = compounds with similar
properties
• Distillation is used to fractionate or separate
fractions of hydrocarbons according to their
boiling points (bp) .
• Distillation towers allow fractions to be
collected at various heights.
• Hydrocarbons have higher bp as their size or
molecular weight increases.
Petroleum Uses
Figure 4.15
Page 170
Figure 4.16 on Page 171
• Liquefied petroleum gas (LPG) is used as fuels
and feedstocks for making plastics.
• Gasoline and diesel are used as motor fuels.
• Gas oil is used for home heating and as a
feedstock for cracking into gasoline fraction.
• Lubricating oil stock (C16-C20).
• Asphalt and waxes (>C20 or bp>370 C)
• Solvents and starting materials for many
products
Natural Gas
• Major component is methane, CH4.
• Heats 2/3 homes in US and widely used in
gas stove or range for cooking.
• Compressed natural gas is used as a
transportation fuel but lacks driving range
and refueling stations.
• Clean burning fuel with little SO2 and NOx
emissions; produces 30% and 43% less CO2
than oil and coal, respectively, on a per
joule basis.
Petroleum Refining
• Cracking or conversion of large gas oil molecules (C15C18) into smaller gasoline molecules (C5-C12) allows
more gasoline to be produced from petroleum.
– C16H34 → C8H18 + C8H16
– C16H34 → C5H12 + C11H22 & …….
• Reforming improves the octane rating of gasoline by
removing hydrogen atoms and converting hydrocarbon
chains into ring structures.
• Cracking and reforming are carried out with catalyst to
reduce energy requirements of thermal cracking.
Fig. 4.17 on Page 173
Isomers
• The formula C8H18 is shared by 18 different
structures or isomeric compounds.
• Isomers have similar chemical and physical
properties.
– Octane is linear but isooctane is branched
– Octane boils at 125 °C vs. isooctane at 99
°C.
– Octane is susceptible to pre-ignition and
engine “knock” but not isooctane.
Octane Rating
• Isooctane is used as a “standard” for measuring
smoothness of engine combustion for gasoline
fuels.
• Isooctane = 100; heptane = 0
• 87 octane = 87% isooctane and 13% heptane.
• Reform octane to isooctane using catalysts (Pt, Pd,
Rh, Ir) to avoid the need for tetraethyl lead,
Pb(C2H5)4; 1976 phaseout.
• Lead oxide emitted into environment is a
neurotoxin and a catalyst poison.
Isomers of Octane
Page 173
4-35 a) Fill in hydrogen atoms to show C8H18 b) Any
duplications of structures? c) C-C-C bond angle? d) C-C-C
bond angle constant in all structures? e) Write the structural
isomer of one more isomer.
Oxygenated Gasolines
• Oxygenated additives improve octane rating and
reduce CO formation.
• Clean Air Act Amendments require MTBE,
methanol, and ethanol to be blended at 2.7% O for
winter gasoline.
• Reformulated gasoline (RFG) with a lower % of
volatile and reactive hydrocarbons has been used
to curb ozone and CO pollution; RFG has benzene
< 1% & oxygenate > 2%.
• Risk: MTBE leaks into groundwater
Synthetic Gasoline
• C + H2O → CO + H2
• CO & H2 are referred to as “water gas” and
used for producing synthetic gasoline (C5C8) or CH4.
• Fischer-Tropsch synthesis uses iron or
cobalt catalyst.
• Feasible in countries (South Africa) where
oil and natural gas are scarce but coal is
plentiful.
Biomass
• Biomass materials are renewable.
• Burning wood; but trees use CO2 and
combustion generates CO2.
• Wood-burning stoves are still
common in developing countries.
• Soot particles affecting human health
is generated.
Resource Recovery from Garbage
• 140 power plants in US burn garbage to generates
electricity; one truckload (27,000 lb) ≅ 21 barrels
of oil.
• Targets energy recovery and waste disposal.
• Japan & Germany rely more on energy-to-waste
technology; 10 % residue to landfill.
• Rural China & India ferment animal and vegetable
wastes into biogas (≅ 60% CH4)
• 2 cows produce enough CH4 for 1 family’s energy
needs for light and cooking fuel.
•
•
•
•
•
•
Ethanol
Fermentation of starch or sugar by yeast
C6H12O6 → 2 C2H5OH + 2 CO2
C2H5OH +3 O2 → 2 CO2+ 3 H2O + 1367 kJ
C2H4 + H2O → C2H5OH (non-renewable)
Gasohol 10% ethanol and 90% gasoline
Ethanol (29.7 kJ/g) has a lower energy density than
gasoline (octane value of 47.8 kJ/g)
• Agricultural interests; food vs. fuel.
• Acetaldehyde in smog is a respiratory irritant.
• Ethanol producers will gain from MTBE ban.
Operations of a Power Plant
Figure 4.23 on Page 181
•Chemical energy in fossil fuels is transformed
into heat energy in the boiler that vaporizes
liquid water to steam for turning the turbine.
•The shaft of turbine is connected to a large coil
of wire that rotates in the magnetic field of the
generator, thereby producing electricity.
Table 4.4 on Page 182
Overall efficiency = 0.60 x 0.90 x 0.75 x 0.95 x 0.98 (electricalÆheat) = 0.34
Example:
Heat needed = heat used x overall efficiency
Heat used = (3.4 x107 kJ) / 0.34 = 1.0 x 108 kJ
Mass of CH4 needed = 1.0 x 108 kJ x 1g/50.1 kJ = 2.0 x106 g CH4
Transforming Energy
• The overall efficiency of energy conversion is the
product of individual steps of transformation
including the efficiencies of theoretical maximum,
boiler, turbine, electrical generator, and power
transmission.
• The theoretical maximum efficiency of power plant is
determined by the conversion of heat to work as
given by
– Theo. Eff. = (Highest T - Lowest T)/Highest T
= (823K - 303K)/ 823K = 63%
• Fuel combustion at elevated pressure helps raise the
boiling point and compresses steam.
Energy Conservation
Figure 4.22 on Page 181
• Fossil fuels are limited; conventional oil reserves
will last 43 years at current rate of consumption,
heavy crude, bitumen, and oil shale will last another
170 years.
• World oil demand increasing at > 2% per year;
faster increase in developing nations.
• Oil is a valuable feedstock for chemicals.
• Increase power plant efficiency to 50-60 %.
• Increase the fuel efficiency (mpg) of cars.
– Require SUVs and pickup trucks to meet fuel
economy standards of passenger cars.
Figure 4.13 on Page 168
Fig. 4.24 on Page 186
Regional Sources of Oil Imported by the
U.S. in 2000; recent shift to Western
hemisphere from the volatile Middle East
Figure 4.25 on Page 187
Fig. 4.27 on Page 190
Energy Conservation
•
•
•
•
•
•
•
New designs for appliances and cars
Green chemistry concepts in production.
Recycling of metals such as aluminum.
Energy efficient light bulbs
Mass transportation
“Smart” buildings
Automation using computers