Energy and the Environment

Science 30: Unit DChapter 1: Limitless energy

1.1- Energy on Demand

• Energy is not a limitless resource; Canadians are not making energy-conscious decisions.• From 1990-2002 a shift towards SUV’s increased fuel

consumption by $370/year compared to cars.• GDP (gross domestic product) is $753 billion; leads to

increase energy use to manufacture goods.• Energy intensity is calculated by dividing energy use

by GDP per year; industrialized countries have low values.

1) Factors affecting usage

Climate: extremes in temperature influence energy usage.• Canada = used to heat homes• Australia= used to cool homes• Changes cause huge variance (47.9 PJ)

Activity: how much work is being done• Measured in $, tones, km travelled.• AS GDP increases; activity increases;

energy usage increases.

Factors affecting usage

• Population: energy use per capita.• Used to measure prosperity of a country.• In order to become prosperous, energy

use is increased= consequences for environment.

• Energy intensity: energy used/ GDP.• Natural resources industry requires more

energy usage = higher intensity.• Since 1990’s Canada has developed a less

energy-intensive economy

2) Energy Efficiency

• Energy transformation is NOT 100%; some is lost as waste energy.

• The desired energy is “useful” energy; the total energy used is the “input” energy.

• To calculate efficiency:• Efficiency = energy (or work) output

energy (or work) input

A) Kinetic and Potential energy example

2. A person on a rollercoaster starts with 345J of Potential energy; the energy at the end of the rollercoaster is 120J of Kinetic energy. What is the efficiency of the rollercoaster?

% efficiency = output energy/input energy

= Kinetic energy/Potential energy

= (120J/345J) x 100

= 34.78%

b) What percent of the total energy is lost as waste energy (heat, sound, etc.)?

100% - efficiency = waste energy %

100% - 34.78% = 65.22%

B) Percentage example3. If a machine is 52% efficient and the total

energy output is 235J; what is the energy input?

% efficiency = energy output/energy input

Energy input = energy output / % efficiency

= 235J/0.52

= 452J

b) What is the energy (in Joules) that is lost to the surroundings?

100% - % efficiency = 48%

0.48 x 452J = 217J

c) Efficiency improvements

• Replacing incandescent light bulbs with fluorescent saves energy.

• From 1990-2002 the energy use in mining decreased by 12% but the amount mined did not.

• Royalties are paid to Alberta’s government by energy companies in order to offset the environmental cost.• Recall Stelmach and the royalty scandal last

year?Gas and Oil

1.3) Harvesting Chemical Energy

• Fossil fuels are used to power engines as well as electronics; where and how they are made is important.

• Discarding rechargeable batteries can lead to soil contamination from heavy metals.

• Energy released in combustion reactions (from fossil fuels) releases carbon dioxide and water vapor.• Chemical potential energy

changes.• Hydrocarbons contain lots of

energy

1) Energy release

• Energy from combustion reactions takes many forms:• Radiant energy (IR and visible light).• Kinetic energy (movement increases)

• Products are at a higher temperature; transfer of energy from hot to cold is called “heat”.

• Energy released is useful “movement” or waste “heat”.

Cars

2) Heat of combustion• Reactants have more

chemical energy – products have more kinetic.

• Potential energy changes in combustion reactions; products have less stored energy than reactants.• Difference = energy released.

• Heat of combustion( ∆cH°) is the energy released during the exothermic (energy released) reaction.

a) Calorimetry

• A calorimeter is used to measure energy transferred to water from the substance being burned.

• An experimental value for heat of combustion is given, but there are errors due to waste energy lost.

b) Hess’s Law

ΔcH° = ∑ΔfH°products – ∑ΔfH°reactants

• Uses standard heat of formation (energy it takes to form a compound) to estimate potential energy.

• Standard heat of formation ( ∆fH°):

• element = 0 kJ• Substances = value from chart (p.5)

Steps

1. Divide into products and reactants.

2. Identify # moles for each

3. Assign values from page 5 table.

4. Total and subtract from each other.

Hess’s law examples

• Calculate the energy change in combustion for the following (use the table):

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

C4H10 (g) + 13 O2 (g) → 8CO2 (g) + 10 H2O (l)

3) Inefficiency of machines

Total energy input = total energy transferred out (First law of thermodynamics).

Some energy will always pass to the environment as heat = 2nd law (always from hot to cold object).

Minimizing the heat loss is the important challenge.

4) Coal-fired generators

• Coal is used to produce more than 70% of Alberta’s electricity.• Converts chemical potential energy into

electrical energy.

• Process:• Crush coal to fine dust, blow into combustion

chamber, IGNITE.• Energy released is absorbed by water lining

the chamber.• Water is converted to steam; causes turbine to

spin--- connected to generator.

Energy conversion:

1. Chemical potential

2. Kinetic energy (steam)

3. Kinetic energy (turbine)

4. Kinetic energy (generator)

5. Kinetic energy (electrical lines)

1.4) Harvesting Nuclear energy

• CANDU = nuclear reactor developed in Canada (Canadian Deuterium Uranium reactor).

• Nuclear energy results from the nucleus of atoms; combining 2 particles or splitting them.

1) The nucleus

• There are 3 subatomic particles in the nucleus:• Proton = positive charge, mass of nucleus,

atomic number.• Neutrons = no charge, mass of nucleus,

responsible for isotopes ( different numbers of neutrons, same protons).

• Electrons = negative charge, orbit nucleus, responsible for charge.

a) Nucleons

Protons and neutrons compose nucleus = nucleons.

Use nuclear notation to describe nucleons:

Mass # - Atomic # = neutrons.

b) Stable Vs Unstable Nuclei

• Stable nucleus = one that will stay together indefinitely

• What makes a nucleus stable?

• Strong Nuclear Force which is much stronger than the electric repulsive forces pushing protons apart.

• Strong nuclear forces only work over very short distances.

• In a large nucleus or a nucleus with extra neutrons, Strong Nuclear Forces don’t work as well and the nucleus is unstable.

2) NUCLEAR REACTIONS

• Chemical reactions, like combustion, only involve changes to electrons.

• NUCLEAR reactions involve changes within the nucleus – new elements are sometimes formed as a result.

• 3 Types of NUCLEAR REACTIONS:• Radioactive decay• Nuclear fission• Nuclear fusion

Nuclear Notation

a) Radioactive decay

• If the force in the nucleus is unstable, the neutron responsible will force the nucleus to split.

• The split nucleus = 2 alpha particles.

• Alpha particle = 2 p+ and 2n (charge = 2+); often written as a helium atom.

• Release of alpha particles = alpha radiation; usually only 1 product is an alpha particle.

Radioactive decay: Types of Radiation

• ALPHA radiation is a particle consisting of two protons and two neutrons (helium nucleus)

• BETA Radiation is high speed electrons produced by changing one neutron into a proton and an electron.

• GAMMA radiation are high energy photons.

1) Alpha decay

Number of radioactive nucleons must balance between reactants and products.

1 product is always an alpha particle ( 4 nucleons, 2 protons).

alpha decay process

steps1. Split reaction into

reactants and products (1 product is always an alpha particle).

2. Create a table.

3. Calculate the mass # and Atomic # of unknown.

4. Identify which element it is (by atomic #).

5. Write the balanced reaction.

reactant product

Mass # 6 4 + AAtomic # 3 2 + Z

63Li ---> 4

2He + ?

2) Beta Decay

• Instability in the nucleus leads to a beta particle (an electron) emission.

• Emitted from the nucleus; a stream of beta particles = beta radiation.

• In beta decay, # of nucleons is constant but atomic # changes; causes conversion of 1 neutron into a proton.

beta decay process

steps1. List reactants and

products.

2. Create a table:

3. Determine mass # and atomic # of the product.

4. Identify unknown product (Atomic # = protons).

5. Write balanced equation.

reactant product

Mass # 10 0 + A

Atomic # 4 -1 + Z

3) Gamma Radiation

• Composed of photons with no mass or charge:

• Usually an excess product of alpha and beta decay.

• Are harmful to humans; considered to be ionizing radiation.

Radioactive Decay

Shielding radiation

• Alpha, Beta and Gamma rays are ionizing radiation and must be shielded.

• A Geiger counter is used to test how much radiation escapes the container (shield).

• Shielding is most difficult for gamma rays because they are the smallest; then beta and finally alpha.

Energy of Different Types of Radiation

• Each type of radiation has a different amount of energy as shown by the penetrating power.

• Alpha is stopped by paper

• Beta is stopped by a thin sheet of copper or a wood or a flesh

• gamma is only stopped by a thick sheet of lead.

Radioactivity

b) Nuclear Fission

• Energy is created by splitting an atom; a large nucleus is struck by a neutron and breaks into 2 smaller nuclei.

• Used in the 1st atomic bomb; used to generate electricity (CANDU reactor).

• Products of the reaction have high kinetic energy; used to spin generators = electricity.

Nuclear Fission

1) Balancing equations

• Same as the steps to balance all other types of radiation.

• Complete the following:235

92U+ 10n ---> 3 1

0n + AZX + 137

53I

2) Controlling the Fission reaction

1) CANDU reactor controls neutrons available by using heavy water = uses heavy hydrogen and oxygen.• Controls the speed of the neutrons.• AKA = moderator (moderates speed).

2) Control rods = lower into Uranium core, decreasing fission reaction #’s.

• Prevents the uncontrolled chain reaction = nuclear meltdown.

Chernobyl Nuclear Meltdown

Chernobyl videos

Chernobyl remembered - MSN Video

3) Mass-Energy Equivalence

• An uranium pellet of 7g can release same amount of energy as 560 L of oil.

• Einstein explained that mass and energy can be converted.

• Mass is the sum of all energy; energy is conserved not mass.

• Uses equation:

E = mc2Energy-mass

a) Energy problems

• A small change in mass can create a huge change in energy.

• Sun converts 4.2 x109 kg into energy per second.

• Balance nuclear equations as usual but find masses from the data booklet.

• Find mass for reactants, products and change in mass.

• Calculate the energy given off.See page 515 problem 1.8

3) Nuclear Fusion• energy of stars

• 2 small masses combine to form larger masses

• Extremely high temperatures required, so fusion reactions are called thermonuclear

• sun temperatures are ~ 15 000 000 ºC

• Fusion bomb = H bomb - fission reactions are used to create high enough temps to have a fusion reaction happen.

• Slow controlled release of energy from a fusion reaction escapes physicists.• Has been pursued for over 40 years• Scientists claimed they had a cold fusion reaction but it

has not ever been proven or replicated.• Ongoing research• Enormous potential energy and the fuel for this type of

reaction is almost unlimited.

Fusion video