chemistry for changing times 12 th edition hill and kolb chapter 15 energy: a fuels paradise john...

Chemistry for Changing Times12th Edition

Hill and Kolb

Chapter 15Energy:

A Fuels ParadiseJohn Singer

Jackson Community College, Jackson, MI© 2010 Pearson Prentice Hall, Inc.

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EnergyMost of all of the energy on planet Earth comes to us from the sun.

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Energy

Energy is defined as the ability to do work or transfer heat.

The SI unit of energy is the joule (J).

(1 J = 0.2388 cal)

The SI unit of power is the watt (W).

(1 W = 1 J/s)

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Energy

Energy can be considered to exist in two forms:

1. Potential energy: Energy of position or stored energy.

2. Kinetic energy: Energy of motion.

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Energy

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Energy and the Life Support System

The biosphere is the thin film of air, water, and soil where life exists. Only a small amount of the energy the biosphere receives is used to support life.30% of solar radiation is reflected back to space.23% of solar radiation powers the water cycle.<0.02% is used by green plants to power photosynthesis. Photosynthesis produces oxygen and stores energy for all animals on the planet.

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Energy and Chemical Reactions

Factors that affect the rate of a chemical reaction include:• Temperature: Increasing temperature

increases reaction rates.• Concentration reactants: Reaction rates are

dependent on reactant concentration. As concentration increases, rate increases.

• Presence of catalysts: Catalysts increase the rate of reactions by lowering activation energy.

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Energy and Chemical ReactionsExothermic reactions release heat energy to the surroundings.

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Energy and Chemical Reactions

Endothermic reactions absorb heat energy from the surroundings.

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Energy and Chemical Reactions

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The First Law of Thermodynamics

Energy can neither be created nor destroyed.

This is also known as the law of conservation of energy.

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The Second Law of Thermodynamics

Energy flows spontaneously from hotter objects toward colder objects.

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The Second Law of Thermodynamics

Entropy is a measure of dispersal of energy. Another way of stating the second law is to say that for all spontaneous processes, the entropy of the universe is increasing.

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People Power: Early Uses of Energy

Early man obtained energy from hunting and gathering of animals and plants.

Plant materials were the first fuels. Even today, wood and dried dung are the principle fuel used by one-third of the people on Earth.

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People Power: Early Uses of Energy

Waterwheels and windmills convert the kinetic energy of moving water and wind into mechanical energy.

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Fossil Fuels

Fossil fuels including coal, oil, and natural gas provide more than 90% of the energy consumed in a modern society.

Fuels are substances that, when burned, release significant amounts of energy. Fuels are a reduced form of matter. Combustion is an oxidation process that is exothermic.

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Fossil FuelsFuels (reduced substances) vs. nonfuels (oxidized substances)

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Reserves and Consumption Rates of Fossil Fuels

Within the lifetime of an 18-year-old, petroleum and natural gas will be consumed to the point that they may no longer be used as fuel.

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Coal: The Carbon Rock of Ages

Coal is a complex mixture of organic material. It is mostly carbon. Carbon combusts as follows:

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Coal: The Carbon Rock of Ages

Coal is ranked from low-grade peat and lignite to high-grade anthracite.

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Coal: The Carbon Rock of Ages

Coal is abundant, and is by far the most plentiful fossil fuel.

It is, however, hazardous to obtain and inconvenient to use due to its solid nature.

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Coal: The Carbon Rock of Ages

Much coal contains sulfur, which when combusted, produces sulfur dioxide (SO2), which contributes to acid rain.

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Coal: The Carbon Rock of Ages

Coal is also a source of other chemical substances.

When coal is heated in the absence of air, the volatile compounds are driven off leaving coke, which is used to produce iron and steel.

The volatile materials can be condensed into coal tar, which can be used as a source of organic compounds for medical and industrial purposes.

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Coal: The Carbon Rock of Ages

The Carbon Cycle

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Natural Gas: Mostly Methane

Natural gas is one of the cleanest burning fossil fuels.

It can also be used as a raw material for the production of many industrial chemicals.

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Petroleum: Liquid Hydrocarbons

By 1950, petroleum had displaced coal as a principle fuel.

Petroleum is a complex mixture of hydrocarbons.

Its combustion with oxygen can be represented as follows:

2 C8H18 + 25 O2 → 16 CO2 + 18 H20

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Petroleum: Liquid Hydrocarbons

Petroleum comes from crude oil, which is separated into fractions for use.

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Petroleum: Liquid Hydrocarbons

A fractional distillation column is used to refine petroleum.

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Petroleum: Liquid Hydrocarbons

Larger fractions can be further refined by cracking into smaller fractions.

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Petroleum: Liquid Hydrocarbons

Gasoline is a lighter fraction from crude oil. It is actually a mixture of more than 150 different compounds.

The gasoline fraction that comes from a distillation column is called straight-run gasoline and does not perform well in a modern, high-compression automobile engine.

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Petroleum: Liquid Hydrocarbons

Octane Ratings of Gasoline

The octane rating of gasoline is a measure of the fuel’s ability to resist knocking. Knocking occurs when the fuel combusts before the spark plug fires.

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Petroleum: Liquid HydrocarbonsOctane Ratings of Gasoline

Isooctane is very resistant to knocking and is assigned an octane rating of 100. Heptane is given an octane rating of zero. Gasoline with an octane rating of 90 performs the same as a mixture of 90% isooctane and 10% heptane.

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Petroleum: Liquid HydrocarbonsOctane Ratings of Gasoline

The octane ratings of gasoline can be improved in a number of ways, including the catalytic reformation of the low octane alkanes into cyclic alkanes with higher octane ratings.

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Petroleum: Liquid Hydrocarbons

Alternative FuelsAutomobile engines can be made to run on nearly any liquid or gaseous fuel.

Diesel fuels are mainly C9-C12 hydrocarbons. Biodiesel is made from animal or vegetable fats and oils.

Ethanol can be used. E-85 is a mixture of 85% ethanol and 15% gasoline.

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Convenient Energy: Electricity

Convenience of fuels depends on the state of matter.

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Convenient Energy: Electricity

Coal Gasification and Liquification

Solid coal can be made more convenient by gasification and liquification.

Electricity is perhaps the most convenient fuel of all.

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Convenient Energy: Electricity

Coal-Burning Power Plant for the Generation of Electricity

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Convenient Energy: Electricity

Percentages of electric power generation in the U.S. in 2003 from various sources.

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Nuclear EnergyNuclear Fission

Nuclear power plants use fission reactions to produce heat to generate steam to ultimately turn a turbine to generate electricity.

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Nuclear EnergyThe U.S. uses much less nuclear energy than many developed nations do.

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Nuclear Energy

Nuclear power plants produce minimal air pollution.

However, many elaborate and expensive safety precautions must be employed.

Also, fission products (nuclear waste) must be dealt with.

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Nuclear Fusion: The Sun in a Magnetic Bottle

Controlled fusion presents many advantages over fission reactors. Radioactive wastes would be minimized. However, technical difficulties must be overcome for fusion reactors to be a reality.

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Nuclear Fusion: The Sun in a Magnetic Bottle

The electromagnet called tokamak is designed to contain the high temperature and pressure plasma of a nuclear fusion process.

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Renewable Energy Sources

Solar Energy

It has been noted that nearly all of the energy available on Earth comes from the sun.

Energy from the sun is diffuse and must be concentrated to make it useful.

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Solar Heating

Solar collectors absorb solar energy and use it to heat water.

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Solar Cells

Photovoltaic cells can be used to convert solar energy into electricity.

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Biomass: Photosynthesis for Fuel

Burning plant material by-products is one means of harvesting energy from the sun.

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Biomass: Photosynthesis for Fuel

Combustion of agricultural waste, fermentation to ethanol or methane, and the fermentation of human and animal wastes to methane have all been and are being used as sources of energy.

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Hydrogen: Light and Powerful

Hydrogen can be burned cleanly as fuel or used in fuel cells.

When hydrogen burns, it produces water and energy.

2 H2(g) + O2(g) → 2 H2O(g) + 572 kJ

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Hydrogen: Light and Powerful

Fuel cells oxidize fuel in an electrical chemical cell to produce electricity.

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Other Renewable Energy Sources

Wind and Water

Both wind (windmills) and water (dams and hydroelectric plants) have been used to turn turbines and produce electricity.

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Other Renewable Energy Sources

Geothermal Energy

In a geothermal plant, water is pumped to the interior of Earth, where it is heated and converted to steam.

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Other Renewable Energy Sources

Oceans of Energy

Ocean thermal energy has been shown to be workable since 1932.

Also, tides and wave action can be converted to useful energy with appropriate technology.

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Energy: How Much Is Too Much?

The demand for energy is ever-increasing and our useful sources are dwindling. These competing demands will cause many changes in our future.