Lecture 18,
th
13
April, 2021
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Energy efficiency
 Electrical home heating: sometimes advertised as being clean and efficient.
Assume that electricity from a coal-burning power plant (efficiency of 37%) is used to
heat a house. If the house requires 3.5 x 107 kJ of energy for heat annually, a typical
value for a city in a cooler climate, how much coal would be burned?
Given: combustion of 1 gram of this particular coal releases about 29 kJ
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Energy efficiency
 Cars and trucks also convert energy from one form to another.
 Internal combustion engine: converts the
potential energy of the gasoline or diesel
fuel into mechanical energy.
 Other mechanisms transform mechanical
energy eventually into the kinetic energy of
the vehicle’s motion.
 Internal combustion engines are even
less efficient than coal-fired power
plants. The thermal efficiency is only
around 20%. Much of the energy is
dissipated as waste heat, including loss
from the internal combustion engine alone.
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Energy efficiency
 Of the 100% energy
available from
combustion, only about
25% actually gets
applied to moving the
car or running the
accessories (+5% for
the parasitic and friction
losses).
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Second Law of Thermodynamics
Newton’s cradle: Do we expect the balls at rest to start
knocking into one another on their own? For this to occur, all
the heat energy dissipated when the balls were colliding would
have to be gathered back together.
This relates to another concept—entropy, a measure of how
much energy gets dispersed in a given process.
Second law of thermodynamics:
The entropy of the universe is constantly increasing. When we lift one of the balls
of the Newton’s cradle, we add potential energy. After the balls knock for awhile and
come to rest, this potential energy has become transformed into the chaotic (and hence
more random and dispersed) motion of heat energy and never the other way around.
The entropy of the universe has increased. The total entropy of an isolated system
can never decrease over time.
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Second Law of Thermodynamics
Entropy: is a measure of the disorder in a
system. All systems gain entropy over time.
The second law of thermodynamics also
explains the inability of a power plant or an
auto engine to convert energy from one type
to another with 100% efficiency.
We always lose usable energy…
For an isolated system, the natural course of events takes
the system to a more disordered (higher entropy) state.
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Bio-fuels
 It is believed that a more sustainable energy future will require the increased use of
biofuels!
 Biofuel: a generic term for a renewable fuel derived from a biological source, such as
trees, grasses, animal waste, or agricultural crops.
 Although most biofuels today are not being produced in a sustainable manner, they
could be in the future.
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Bio-fuels
 All of the biofuels contain some oxygen. As their oxygen content increases, biofuels
release proportionately less energy per mass burned than hydrocarbons.
 Wood, the most common biofuel, has been used throughout human history for
cooking and heating. Wood contains cellulose, a naturally-occurring compound
composed of C, H, and O that provides structural rigidity in plants, shrubs, and trees.
Similar to hydrocarbons, cellulose is made up of carbon and hydrogen.
 Cellulose is a natural polymer of glucose, that is, a chain of thousands of glucose
molecules linked together.
 Wood is in insufficient supply to meet our energy demands. Cutting down trees for
fuel also destroys trees that effectively absorb CO2 from our atmosphere. So instead
of relying on wood, people in all sectors are eyeing liquid fuels such as ethanol.
 Ethanol is an example of an alcohol, a hydrocarbon substituted with one or
more –OH groups (hydroxyl groups) bonded to its carbon atoms.
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Bio-fuels
 Just like hydrocarbons, alcohols are flammable and
burn to release energy. With complete combustion, the
products are CO2 and H2O.
 With >13,000 million gallons of ethanol produced annually in 2011, the USA is the
world’s largest ethanol producer. Brazil is second, (~7000 million gallons) of
ethanol. Together, these two countries account for about 85% of the world’s
production. Corn is the raw material in the US. In contrast, Brazil derives almost
all of its ethanol by fermenting sugarcane. Practically any sugar or grain can be
fermented to produce ethanol. The substance fermented depends on its availability,
economics, and politics.
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Bio-fuels
 Regardless of its source, ethanol doesn’t go
straight into the gas tank because our
automobiles are not engineered to burn it.
 However, auto engines can run on “gasohol,” a
blend of gasoline with ethanol. For many years,
gasoline typically contained 10% ethanol.
These blends now are labeled E10.
 Beginning with legislation launched in 2007, the USA sought to reduce dependence
on oil imports and increase the use of renewable fuels. As a result, a shift to E15 was
proposed. E15 is 15% ethanol, 85% gasoline.
 The octane rating of a gasoline increases as more ethanol is
added. But with more ethanol, the gas mileage decreases slightly.
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Bio-diesels
Note: Biofuel is any fuel that is derived from sources of biological origin, typically
plants. All variations of biodiesel are thus types of biofuels.
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Bio-diesels
Biodiesel: made primarily from vegetable oils (soy, palm, rapeseed); also from waste
cooking oil; or animal fats.
Triglycerides: includes both fats and oils. Fats like butter and lard: are solids at room
temperature. Oils like olive and soybean oil: liquids. Triglycerides occur naturally in both
plants and animals and are starting material for biodiesel.
Although triglycerides will burn, before being utilized as a fuel, they need to be first
snipped into smaller pieces closer in size (and ease of evaporation) to the molecules in
diesel fuel. Can be done by reacting them with an alcohol like methanol (CH3OH) and a
catalyst sodium hydroxide (NaOH).
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B20: mixture of 80% petroleum
diesel and 20% biodiesel.
For your reading and understanding!
Ethical Principles to Apply to Current
and Future Use of Biofuels
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Biofuels – an answer or a problem?
Disadvantages
Advantages of biofuels
Less energy-efficient
Renewable
Still generate CO2
Capture CO2 from atmosphere
Requires land –clearing forests
Release less CO2 per mile of
Distorts food markets
driving
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New Uses for an Old Fuel
 World supplies of coal predicted to last much longer than current estimates
of oil reserves.
 Coal (solid): inconvenient for applications, such as fuel for vehicles.
 Projects aim to convert solid coal into fuels with characteristics similar to
petroleum products.
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Just for your idea; will not come in exam…
New Uses for an Old Fuel
 Before large supplies of natural gas were discovered and exploited, cities were lit with
water gas, a mixture of carbon monoxide and hydrogen.
 Formed by blowing steam over hot coke (impure carbon
remaining after distilling volatile components from coal.
 This is the starting point for Fischer–Tropsch process for producing synthetic
gasoline from coal. German chemists Emil Fischer and Hans Tropsch developed this
process (1920s) when Germany had abundant coal reserves, but little petroleum
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Clean Coal Technology
 The use of coal in Asia, particularly in China, is skyrocketing, as China has enormous
coal reserves to fuel its rapid growth.
 However, coal burning (by any nation) clearly
does not meet the criteria for sustainability.
 Is Clean Coal Technology a myth?
 When scientists talk about clean coal
they are usually referring to two methods:
High-efficiency, low-emissions
technologies and carbon capture and
storage.
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Just for your idea; will not come in exam…
Clean Coal Technology
 Variety of methods that aim to increase the efficiency of coal-fired power plants
while decreasing harmful emissions.
 “Coal washing” to remove sulfur and other mineral impurities from
the coal before it is burned.
 “Gasification”: convert coal to a mixture of CO and H2; resulting
gas burns at a lower temperature, reducing the generation of NOX.
 “Wet scrubbing” to chemically remove SO2 before it
goes up the smokestack; accomplished by reacting
the SO2 with a mixture of ground limestone and water.
 None of these technologies address greenhouse
gas emissions.
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Thought of sharing these important facts
on energy with you! You do not have to
memorize but this is just for your idea.
A contextual
comparison of
various energy
magnitudes!
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Energy and power
Power : energy produced per second.
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Endothermic Reactions
Photosynthesis: endothermic.
Requires the absorption of 2800 kJ of sunlight per mole of C6H12O6, or 15.5 kJ per
gram of glucose formed. The complete process involves many steps, but the overall
reaction can be described with this equation.
Other examples of endothermic reactions are: O3 →O2 +O; N2 + O2 → 2NO.
(First requires photon energy; second requires high temperature)
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Endothermic Versus Exothermic Reactions
Photosynthesis: endothermic.
Requires the absorption of 2800 kJ of sunlight per mole of C6H12O6, or 15.5 kJ per
gram of glucose formed. The complete process involves many steps, but the overall
reaction can be described with this equation.
Sunlight
Note: Glucose is formed (15.5 kJ/g) vs. Glucose is combusted (-14.1 kJ/g), the
magnitudes vary because in the former, glucose is formed from CO2 and water (liquid);
in the latter, glucose burns to produce CO2 and water (gas).
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Introduction
 Nearly 60% of human body is made of water
 >70% of the earth surface is covered with water
 Only common substance that can exist as a solid, a liquid,
or a gas at average earth temperatures!
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Introduction
If climate change is a shark, then water is its teeth— James P. Bruce
 Earth’s fresh water resource: i) not unlimited
ii) not renewable fast enough to meet the needs
of our increasing world population.
 This makes water a strategic resource. Its scarcity invokes conflicts and
raises questions of who has the right to access and use it.
 In 1993 the UN General Assembly proclaimed March 22 as
International World Water Day.
5th June?
world environment day
16th September?
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Molecular structure of water
 Electrons are not shared equally in the O–H covalent bond.
 Electronegativity difference between oxygen and hydrogen: 1.4
 O–H bond: electrons are pulled closer to the more
electronegative oxygen atom. Also shown
experimentally.
H2O, a polar
molecule with polar
covalent bonds
 The greater the difference in electronegativity between two bonded atoms, the
more polar the bond is.
 Each H atom carries a partial positive charge (δ+), and the oxygen atom carries
a partial negative charge (δ-).
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This is how you can visualize the electronegativity
Electronegativity and Polar bonds
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Electronegativity and Polar bonds
Electronegativity Values
for Select Elements
 Fluorine and oxygen have the highest values.
 Metals such as lithium and sodium have low values.
 Values increase from left to right in a row of the periodic table (from metals to
nonmetals) and decrease going down a group.
 Greater the difference in electronegativity between two bonded atoms, the more
polar the bond is.
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Electronegativity and Polar bonds
 If it is greater than 2.0, the bond is considered ionic. Use this information as a
guideline rather than as a rule.
 What about CO2 molecule?
 A nonpolar covalent bond is a covalent bond in
which the electrons are shared equally or
nearly equally between atoms.
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The Unique Properties of Water
 Water: important for small scale processes:
 dissolves many substances
 essential medium for biochemical reactions in cells
Water: Elixir of life
 What happens if water content in our body is reduced by2%: get thirsty
5%: feel fatigue, have headache
10–15%: muscles would become spastic, we would feel delirious
>15%: dehydration could cause death
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The Unique Properties of Water
 Liquid at room temperature and normal atmospheric pressure.
 Almost all other compounds with similar molar masses are gases under those
conditions, like N2, O2, and CO2 with respective molar masses 28, 32, and 44
g/mol, greater than water (18 g/mol)!
Water: important for shaping large-scale processes
 In its three forms, ice, liquid water, and water vapor (humidity),
water affects daily weather and the climate of a region
 Ice (0.9167 gm/cm3 at 0°C) is less dense than water (0.9998
gm/cm3 at 0°C) and floats on water causing ecosystems in lakes
and streams to survive beneath the ice during frigid winter days
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The Unique Properties of Water
Remember: Water is most dense (1 g/cm3) at 4°C. At 0°C, it is slightly less
dense (0.9998 g/cm3).
Ice (0.9167 gm/cm3 at 0°C) is less dense than water at 0°C.
 In winter, ice floats on lakes instead of sinking. This topsy-turvy behavior means that
surface ice, often covered by snow, can act as an insulator and keep the lake water
beneath from freezing solid.
 Aquatic plants and fish thus can live in a freshwater lake during cold winters. And
when the ice melts in spring, the water formed sinks, helping to mix the nutrients in
the freshwater ecosystem.
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The Unique Properties of Water
 High capacity to absorb and release heat!
 Specific heat: quantity of heat energy that must be absorbed
to increase the temperature of 1 gram of a substance by 1°C.
 Water: 1 cal/g°C or 4.186 joule/g°C.
 Or 4.18J of heat must be removed in order to cool 1g of
water by 1°C.
 Water has one of the highest specific heats! So water is an
exceptional coolant. When water evaporates, it can carry
away the excess heat in a car radiator, in a power plant, or in
the human body.
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