ch 4 - energy

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CH 4 - Energyhttp://www.ncga.com/ (National Corn Growers Association)http://www.doe.gov http://www.ucsusa.orghttp://www.epa.gov http://www.citizen.org

Chapter 4: Energy, Chemistry, and Society

ENERGY?

Like the energy of a crowd, You can’t see it,Can’t measure it,But you know it is there.

What do you think of when you hear the word

Annual per capita energy consumption (1997)

Sources of Electrical Energy in the US.

Coal 56.9%Nuclear 19.5%N. Gas 9.4%Hydro 8.3%Petroleum 5.5%Other 0.5%

1988 data)(En. Infro. Adm. Annual Rev.

Three Gorges Dam in China – hydroelectric power.

4.6

How do Different Fuels Stack Up?

High E content and the only product of its combustion is water!

Energy is the capacity to do work.

Work is movement against a force (w = f x d).

Terms that need to be defined:

Heat is energy that flows from a hotter to a colder object.

Temperature determines the direction of heat flow.

4.1

Heat is a consequence of motion at the molecular level; temperature is a measure of the average speed of that motion.

4.1

What are units of heat?

The joule (J): 1 J is the amount of energy required to raise a 1-kg object 10 cm against the force of gravity.

The calorie (cal): 1 cal is the amount of heat required to raise the temperature of 1 g of water by 1 oC.

1 calorie = 4.184 J1 kcal = 1000 cal = 1 Cal (1 dietary cal)

So that 450 Cal doughnut is really 450,000 calories!

First law of thermodynamicspotential/kinetic energy

• First Law: The energy of the universe is constant,

4.2

or, energy can neither be created nor destroyed; but it can be converted from one form to another.

Potential energy is energy due to position or composition.

Kinetic energy is energy due to movement.

4.2

Diagram of a Power Plant

heat

work electricity

4.2

Potential energy(chemical bonds)

Heat energy

Mechanical energy

Electrical energy

burner

gas turbine

generator

The First Law of Thermodynamics Energy is neither created nor destroyed, but may be transformed from one form

to another.

Taking random, thermal energy and transforming it into ordered work goes against the Second Law of Thermodynamics.

Second Law of Thermodynamics The entropy of the universe is

increasing.

Power plants are inevitably inefficient

There is no free lunch!

4.3

Bomb calorimeters can be used to determine the heat of combustion.

If you test a reaction that releases heat, the temperature of the water will increase.

4.3

CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l) + ENERGY

Hydrocarbon fuels like methane (CH4) burn in the presence of oxygen to produce carbon dioxide and water.Energy is released in this process called combustion.

When energy is released during the course of a chemical reaction, it is said to be an EXOTHERMIC reaction.

The combustion of methane gas releases 50.1 kJ/g of CH4

This is the equivalent of 802.3 kJ/mol CH4

4.3

CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l)

Net energy change is - 802.3 kJ/mol CH4Exothermic

reaction

The products are lower in energy than the reactants.Exothermic reaction: E is a negative value

4.3

Activation energy is the energy required to initiate the reaction.

Molecules must possess enough energy so that their collisions

will be productive- leading to products.

ENDOTHERMIC reactions will have products higher in energy (E will be positive) than the reactants; there will still be a required activation energy.

Exothermic reaction

4.4

Energy Changes at the Molecular Level

The energy changes are due to the rearrangement of the atoms of the reactants and products; it is the breaking and forming of bonds that dictates if a reaction will be endothermic or exothermic.

Bond energy is the amount of energy that must be absorbed to break a chemical bond.

energy

Breaking bonds ALWAYS requires energy!

4.4

4.4

Consider: 2 H2 + O2 2 H2O

Bonds breaking2 H-H + O=O

Bonds forming4 O-H

(2 H-O-H)

4.5

History of U.S. Energy Consumption by Source 1800-2000

1 EJ = 1018 J

4.6

How Do Different Fuels Stack Up?

High E content and the only product of its combustion is water!

Coal

• Coal is a complex mixture of substances. Although not a single compound, coal canbe approximated by the chemical formula C135H96O9NS.

• U.S. reserve estimates range from 150 to 250 years.

4.6

Petroleum – from where does the U.S. import it?

2005: U.S. consumption was almost 22 billion barrels A DAY.

Over 60% of it was imported.

The U.S. has 5% of the world’s population, yet consumes 25% of the oil produced worldwide.

4.7

Fig. 4.25 – Energy consumption pattern, 2000. Green=oil, red=natural gas, yellow=nuclear, blue=hydroelectric, purple=coal.

4.7

One of the drawbacks to petroleum is that it must be refined before use.

4.7

How do we use each barrel (just under 45 gal) of petroleum?

This 1.25 gal includes nonrenewable feedstocks for all plastics, pharmaceuticals, fabrics and other carbon-based products.

Over 87% of each barrel is used for transportation and heating.

Manipulating Molecules to make Gasoline

Processes that improve octane rating:1. branching of hydrocarbons2. adding tetraethyl or tetramethyl lead to make leaded gasoline (banned 1976)3. adding 10% ethyl alcohol to gasoline

to make gasohol (why only 10%)

4.7

A Port Arthur, TX Oil

Refinery

A Port Arthur, Texas Oil Refinery

4.9

Gasoline AdditivesElimination of octane enhancing tetraethyl lead (TEL) created a need to find substitutes.

H3CO

CCH3

CH3CH3

CH

H

CO

H H

HH

MTBE –methyl tertiary-butyl ether

Ethanol (ethyl alcohol)

Human health effects of exposure to MTBE are not known.

Fuel AlternativesBiodiesel fuel use is on the rise. Made from natural, renewable sources (veg oils, animal fats), it can be used as pure fuel or blended with petroleum.

Ethanol is renewable, but more expensive than gasoline. •Some believe it takes more energy to produce a gallon of ethanol than you will obtain from burning it.•Controversy: National Corn Growers vs. American Petroleum Institute.

4.10

Alternative Fuels• Converting coal to liquids and gases;• Converting coke and steam to what is

known as water gas (carbon monoxide and hydrogen);

• Converting water gas to hydrocarbons by a method known as the Fischer-Tropsch process (Germany);

Alternative Fuels• Biomass: converting materials to fuels

by biological processes. For instance, ethanol (alcohol) can be produced by the fermentaion of carbohydrates such as starches and sugars or agricultural products. Four million vehicles in Brazil use pure ethanol.

Fig. 4.20

Alternative Fuels• Methanol, is another alcohol that is being

used in engines of racing car • Garbage: burning garbage to make

electricity. Ex. Minneapolis has one of the 140 power plants in the US that uses garbage to produce electricity. (resource recovery approach or waste-to-energy technology)

• 1 truckload of garbage = 21 barrels of oil

Fig. 4.21- Garbage burning power plant – Minneapolis – meets the needs of 40,000 homes.

Conservation of Energy and Matter• In short, the arguments for

conserving energy and fuels are compelling.

• Since the oil crisis in 1974, many strategies have been implemented to conserve energy in spite the fact that our consumption had increased.

Conservation of Energy and Matter• Here are some strategies:1. Improve efficiency of energy

systems (appliances, furnaces, etc.).

2. Improve efficiency of power plants from its current value of 42% to 50-60% using cogeneration.

Conservation of Energy and Matter

3. A Scientific American article in September 1990 claimed, ”If a consumer replaces a single 75-watt bulb with an 18-watt compact fluorescent lamp that lasts 10,000 hours, the consumer can save the electricity that a typical U.S. power plant would make from 770 lbs of coal. As a result, about 1600 lbs of CO2 and 18 lbs of SO2 would not be released into the atmosphere.”

Conservation of Energy and Matter

4. Encourage utility companies to educate consumers on how to conserve energy.

5. Give financial incentives.6. Recyle materials especially aluminum.

Recycling 250,000 aluminum cans saves energy equivalent to 3.5 gallons of gasoline. In other words, you could watch TV for 3 hours on he energy saved by recycling just one can.

Conservation of Energy and Matter

7. Transportation: About one-fourth of the total energy used

and one-half of the world’s oil production goes to power motor vehicles.

8. Use public transportation. In Japan, 47% of travel is by public transportation, compared to 6% in the U.S. .

Fig. 4.27 – Fuel Economy (CAFÉ)

Toyota Prius – gasoline/battery hybrid car.

Honda Civic