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

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 CH4

Exothermic 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

18.7% increase each year

0

100

200

1980 1990 2000

Pro

ved

Re

serv

es,

Gb Saudi

Iran

Iraq

Kuwait

UAE

OPEC Oil “Proven” Reserves!

• Accurate reserve estimates for OPEC countries are closely guarded state secrets• Values for 1983 are probably accurate (for 1983)• 430Gb rise in reserves, no adjustment for 193Gb produced since 1980• These questionable reserves are 45% of world oil reserves used by IPCC!• A recent leak of Kuwait Petroleum Company documents showed the actual reserves are only 48Gb

(official reserves are 102Gb)• 1980 Kuwait reserves adjusted for production since then are 55Gb

From BP Statistical Review

Not provenby anybody!

Gb = billions of barrels

World Oil Production Peaked in May 2005non-OPEC Peaked in 2004Saudi Arabia peaked in 2005, Russia appears to have peaked

IEA stillpredicts an increase(May 19, 2009)

MBD

Year

Existing oil fields are declining at - 6.7% per year (IEA 2008)

For 2005 to 2030 the world needs 45 mbd of new production – just to maintain flat production

The projected growth requires discovery of 45 + 12 = 57 mbd of new oil!

Existing Oil Fields are in Decline

57 ÷ 9 = ~6+ We need 6 new Saudi Arabias!

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 can

be 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

4.7

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

4.7

A Port Arthur, TX Oil

Refinery

A Port Arthur, Texas Oil Refinery

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.

4.9

Gasoline Additives

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

H3CO

CCH3

CH3

CH3

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 Alternatives

Biodiesel 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. •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