An attempt to take ideas about Energy and Conservation from several disciplines and form an integrated organization.

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Statements about energy from various sources:

1. There are many forms of energy: wind, water, sun, potential, chemical, electrical, nuclear, light, motion, heat, mechanical, internal, external, atomic, nuclear, molecular, gravitational, bond energy, bonding energy, sound energy etc. Energy can change from one form to another. Energy is Conserved

2. Potential Energy can be stored in an atom or nucleus or molecule or by gravity or in a battery” 3. Work: Force times Distance= KE= 1/2 mv2 PE= mgh

4. In an exothermic reaction heat is given off by a chemical reaction. The energy comes from substances involved. 5. Electricity often turns into heat

6. A windmill can turn wind energy into electrical energy

7. Nuclear energy is very large and comes from the nucleus! Both fission and fusion produce energy.

8. Potential energy is in a form you often cannot see.

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Where does the confusion about energy come from?

1. Why is it “work” to push on a wall? We get tired! Books say no work is done!

2. Do these topics have any conceptual similarities as we teach them. Biology (sun energy, cell energy, chemical energy, potential energy), Physics (mechanics:gravitational potential energy and kinetic energy, frictional heat energy), thermodynamics: heat transfer, nuclear and electrical energy), Chemistry (thermochemistry, bond energy, nuclear energy, heat of reaction, heat of fusion and evaporation and in all areas The Law of Conservation of Energy

3. How do you describe how energy is stored in molecules and bonds and the nucleus?

4. In an exothermic reaction where exactly does the heat come from? At the atomic level what is the same for all exothermic reactions? 5. What is the connection between mass and energy?

6. How is electrical energy related to the equations of Mechanics in Physics?

7. How are all the different Forms of Energy..mentioned in most texts …..related? Are there really so many different forms of energy?

8. How is Work done actually related to PE, KE, heat, electricity ?

9. How is Binding Energy related to energy given off in nuclear reactions? Is Binding Energy a form of energy?

10. What do all the forms of Potential Energy have in common?

energy definitions.url

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…………………………………Some confusing definitions…………………………..Definition: Energy is the capacity of a physical system to perform work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or other forms.

Energy Definition: Energy may be defined as the ability to do work. It is a scalar physical quantity. Although energy is conserved, there are many different types of energy, such as kinetic energy, potential energy, light, sound, and nuclear energy… a form of power such as , electricity, heat or lightthat is used for moving things around…work.…the power that is present in all physical things and that can be changed into something such as heat, movement or light.

Electrical energy is the movement of electrons. That is kinetic energy. The voltage in an electrical circuit is the potential energy that can start electrons moving. Electrical forces cause the movement to occur.

Chemical energy is potential energy until the chemical reaction puts atoms and molecules in motion. Heat energy (KE) is often the result of a chemical reaction. Confusion also comes from using “h” instead of h for example in “mgh” and Vlost instead of V in V=IR and energy = VIt etc etc

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The following are examples using consistent concepts of KE and PE throughout science

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Definitions that prove consistent throughout the curriculum:

1. Work is the Transfer of Energy from one form or condition to another. Mass=Energy is always Conserved in all interactions

2. There are 3 forms of energy: kinetic, potential and electromagnetic.

(Mass is converted into Energy via E= ΔmC2)

3. Kinetic energy may assume the form of Macroscopic 1/2 MV2 or Microscopic Heat. (Heat in or out can be calculated)

4. Potential energy is associated with the relative positions between bodies. Most common: Since all molecules and atoms and opposite charged ions attract each other …Potential Energy goes UP when attracting bodies move away from each other and goes down when they approach…at least until they get to their “bond distance” in which case repulsion becomes greater than attraction. Ultimately all losses PE involve mass being converted into energy.

5. Electromagnetic energy refers to any of the electromagnetic spectrum.

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Examples of sources of potential energy in systems1. Gravitational: Masses attract the earth…when moved further away PE goes up.

2. Electrostatic

A. Electrical: When electrons are moved from protons PE goes up; when electrons are moved closer together PE goes up. …as in charging a capacitor etc.

B. Chemical: Anytime PE goes up: Sum of attracting bodies get further apart and repelling bodies get closer together. It often is difficult to see all of this but if you analyze simple systems you can see it at work.

4. Nuclear: In any exothermic nuclear reaction…be it fusion or fission it can be shown that potential energy goes down because attracting bodies are getting closer…the nuclear force of attraction is much larger than the electrostatic forces of repulsion.

Potential energy can be shown in graphical form for ALL changes….not just chemical reactions.

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1/2 M V2

Kinetic Potential Electromagnetic

Heat

For now EM isleft out of the scheme.

Within each categoryWithin each categoryenergy can go from oneenergy can go from onebody to anotherbody to another

A C

B

E=MC2

Macroscopic KE

Microscopic KE

D

A and B C D 10

Conversions within a category

1. Potential Energy: a. Chemical PE -----Electrical PE: Battery charging capacitor b. Gravitational PE-----Spring PE: A mass set atop a spring compresses it.

c. Chemical PE -----Gravitational PE: Lift a box 2. Kinetic Energy a. Microscopic KE: Heat flows from hot to cold b. Macroscopic KE: Two billiard balls collide.

3. Electromagnetic Energy a. Fluorescence: UV changed to Visible light

1/2 M V2

Kinetic Potential Electromagnetic

HeatWithin each categoryWithin each categoryenergy can go from oneenergy can go from onebody to anotherbody to another

A C

B

1. Expanding gases cool: B to C Compress gases: C to B2. Water evaporates and cools: B to C Water condenses: C to B3. Wax freezes on your finger: C to B Wax melts: B to C4. Car brakes to a stop: A to B Engine accelerates car: B to A5. Exothermic chem reaction: C to B Endothermic chem reaction: B to C6. Bullet shot from gun: C to B & A Car bounces down on springs: A to C7. Car coasts up a hill: A to C Car coasts down a hill: C to A8. Driver brakes down a hill: C to A & B Car brakes going up a hill: A to B & C9. Pendulum: C to A and A to C Eventually: all ends up as B10. Drop a book on the table: C to A to B Pour hot water into cold: B to B11. Lift a rock:Cbody to Cgravity Push on the wall: C to B12. Pool balls collide: Aball 1 to Aball 2 A mass compresses a spring: Cgravity to Cspring

13. Battery lights light bulb: C to B etc Electric motor: Celectrical to A and B

E=MC2

E=MC2

The Law of Conservation of Energy

Energy is never destroyed; it just changes forms. (JUST CONSIDER POTENTIAL AND KINETIC )

PE + KE = CONSTANT

Example: 5 + 5 = 10 6 + 4 = 10 8 + 2 = 10

If PE gets bigger then KE gets smaller

Boils down to: KE + PE = 0

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A good definition belowThe bonds between atoms are the source of all chemical or covalent type have relatively

low potential chemical energy, as it requires a large amount of outside energy simply to

break the bonds. Weaker bonds, like those of the van der Waal type, have more potential chemical energy, as they require relatively

little energy to break. Energy is released when these bonds form between atoms, and the energy in chemical reactions is not created or destroyed. This

means that chemical reactions may be analyzed like mathematical equations. Since a

strong bond requires a large amount of energy to break, this must mean that when

that same bond forms, much energy is released. By the same logic, when a weak

bond forms, relatively little energy is released.

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Hydrogen gas + chlorine gas ==== hydrogen chloride gas

PE

Coordinate

………………………………………………

……………………………..

H + H

H2

Cl + Cl

Cl2

Exo Endo

H + H + Cl + Cl

2H = H2 + heat 2Cl = Cl2 + heat 2H + 2Cl = 2HCl + heat H2 + Cl2 = 2HCl + heat

Exo Endo

Exo Endo

H2

Cl2

PE average

Exo

The Net reaction is Exothermic because the bond distances between hydrogen and chlorine are smaller than between hydrogen-hydrogen or chlorine-chlorine…PE is down.

74 + 199 > 2 ( 127 ) bond distances pm

273 > 254

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A Simple Chemical Reaction

C(g) + 02 (g) ------ CO2(g) + heat

PE + KE PE + KE

C + O O

O

O

PE

Coordinate

O2 + C

C + O + O

CO2…………………….

Atoms are closer together

PE + KE = 0

121 > 113

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Combustion of Methane

2 O2

Ch41640 kj/mole

992 kj/mole O2

120 pm

109 pm bond length

+2632 kj/mole ch4 -3338 kj/mole methane

2 H2O1852 kj/mole methane

CO2

1486 kj/mole

96 pm

116 pm

1 CH4 + 2 O2 2 H2O + CO2

916 > 848

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Thermochemistry

1. Hot water is mixed with cold water H = MC T= KE change

Δ Hhot water + Δ Hcold water = ZERO

[ (35g)(1cal/gC)(T2 - 80C)] + [(19g)(lcal/gC)(T2 - 24C)] = 0

T2 = 60 C

Kinetic energy fallsKinetic energy falls Kinetic energy rises Energy Conserved

For example: Suppose 35ml of 80C water is mixed with 19ml of 24C water. What is the resulting temperature? (60 C)

Heat energy is transferred from hot object to a cooler one.

HOT COLD

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Determining the Specific Heat of Iron2Heat a 1.0 kg mass in water to about 80 c. Place 200 ml tap water in a styrafoam cup, measure temp. and insert mass.

Kg

T1 Water = 22.2C

T1 iron = 81.2 C

heat 0 = heat lost by Fe + heat gained by water

0 = mc Δ t iron + mc Δ t water

0 = (1000g) (CFe) (T2-81.2C) + (200g) (1cal/gC) (T2-22.2C) 200.0 ml water

Measure T2:

Insert the final temperature and solve for CFe

Notice that in the following problemsthat delta T can always be interpretedas T2 – T1 and no confusion of what to do.

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Some examples1. Going from solid oxygen to nucleons.

PE

solid

Liquid

Gas

Atoms

Nucleons

1

2

3

4

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1-2. O2(s) + energy --- O2(L) 2-3 . O2(L) + energy ----- O2( g ) 3-4. O2(g) + energy ---- 2 O(g)

4-5 O(atom) + Energy ----- O(ion) + 8 electrons 5-6 O(ion) + Energy ---- 8 protons + 8 neutrons

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Ions

Endothermic

Exothermic

Δ PE + Δ KE = 0

up down

Δ PE + Δ KE = 0

down up

Getting fu

rther apart

Getting closer together

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O

O

O

O

O

O

O

O

O

PE

KE

TotalEnergy

Heat Ice Melt IceHeat Water

VaporizeWater

HeatVapor

Decomposewater

Heatatoms

Ionizeatoms

Heationz

NucleonsIce…to....nucleons thru heating

*

*

*

*

*

solid

liquid

gasatoms

ions

nuceons

*= phase change

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Demonstration Have a student insert one finger into 60F liquid wax and anotherinto 60F water. Essentially both will feel the same.

Now remove both fingers: the wax gets hotter as it freezes and thewater gets cooler as it evaporates.

PE

Water

Wax

Liquid

Gas

Liquid

solid

PE

Heat Absorbed Heat given off

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Ice in WaterICE

0 CWater

Heat from the water is used to (1) melt the ice and (2) warmthe resulting ice water.

heat

PE ice KE water

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Burn methanol with oxygen to make carbon dioxide and water + heat

113 pm

96 pm

121 pm

108 pm

143 pm

95 pm

= 2 3 2 4

0 = KE + PE

1850 total to 1672 total = atoms closer together and PE down

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Thermochemistry20g of wax at 80C in mixed with 50ml of water at 25C. What is the final temp?

Fd = Δ PE + Δ KE (macroscopic) + Heat

0 = (Mass x H fusion wax) + [(Mwax x Cwax T) + (M x Cwater T)]

0= [(20g)( - 20cal/g)] + [(20g)( 0.1cal/gC)(T2 - 80C)] + [(50g)(1cal/gC)(T2 - 25C)] Heat of fusion is (-) PE goes down cools heats

0 = ( - 400) + 2T2 + ( - 160 ) + ( + 50T2) + ( - 1250 )

0 = - 1810 + 52 T2 T2 = 35 C no confusion about t

0 = ( - ) + 0 + + ( - ) + ( + )

Liquid Hot Wax WaterSolid Hot Wax28

Dissolving

Some compounds are exothermic when dissolved, some are endothermic when dissolved and somedon’t seem to affect water temperature when dissolved

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Dissolving of Ammonium Chloride Endothermic

NH4Cl (s)

NH4 +1 (g) + Cl-1 (g)

NH4 +1 (aq) + Cl-1 (aq)

DISSOCIATION(lattice energy)

HYDRATIONPE

PE

H = +18 KJ/MOLE

+1 -1

+1 -1

+1 1

Note: H20 = 0 =

0

0

00 0

0

0

0

+-

+ 705 kj/mole

- 307 kj/mole - 381 kj/mole

-

0

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Dissolving of Sodium Hydroxide exothermic

NaOH (S)

Na +1 (g) + OH -1 (g)

DISSOCIATION

PE

Na+1 (aq) + OH-1 (aq)

HYDRATION

+1 -1

+1 -1

+1 -1o

o

oo

oo

oooo

oo

PE

H = - 45 kj/mol

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Dissolving of Sodium Chloride very slightly exothermic

NaCl (s)

Na+1 (g) + Cl-1 (g)

Na+1 (aq) + Cl-1 (aq)

+787 kj/mol

-406 =

- (406 +363) = -788 kj/mol

HYDRATION

DISSOCIATION

PE

Delta H = -1 kj/mol

+1 -1

+1 -1

+1 -1oo

o

o o

oo

o

o

o

o

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ThermochemistryExample: Add 5.0 g of ice at 0C to 100ml of water at 25C. What is the final temp?

Δ H = mC(specific heat) Δ T = Δ KE Δ H = m (Hf) ….heat of fusion = Δ PE

Δ Hice =(5.0g) (+80 cal/g)H25C water=(100g)(1cal/gC)(T2-25C)

Hice water=(5.0g)(1cal/gC)(T2-0C)

Δ H total =(100g)(1cal/gC)(T2-25C) + 5.0g)(1cal/gC)(T2-0C)+ 5.0g) (+80 cal/g) = 0 KE goes down + KE goes up + PE goes up = 0

Δ KE + Δ KE + Δ PE = 0 ( - ) ( + ) ( + ) Conservation of Energy

100T2 - 2500 + 5T2 - 0 + 400 = 0 Final Temp = 20C

(Use +80 when PE rises and -80 when PE falls;when a substance freezes the attracting particles get closer together and PE goes down. This also happens with water but because of hydrogen bonding its less obvious to see….ice floats)

warm water cools cool water heats ice melts

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Exothermic ReactionsA. 2.0g (0.050mol) of Na0H are put into 300ml of water at 22C and the temperature rises 2.5C. What happened to the Potential energy of the Na0H?

Fd = Δ PE + Δ KE (macroscopic) + Heat

0 = Δ PE + 0 + heat

0= Δ PE + mC Δ T0= Δ PE + (300g)(1cal/gC)(+2.5C) chemical PE is lost and KE transferred to the water

Δ PE= -750 calories The reaction is EXOTHERMIC!

B. 0.10mol of Ammonium Chloride dissolves in 250ml of water and the temp drops from 24C to 21C. What is the H of the reaction?

Fd = Δ PE + Δ KE (macroscopic) + Heat

0 = Δ PE + 0 + mC Δ T

0= Δ PE + (5g)(1cal/gC)(21C-24C) KE is lost by the water and converted to PE in the chemical system

0= Δ PE + (-15cal) Δ H = + 15cal or + 150cal/mol ENDOTHERMIC!

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Line Spectra : Δ PE + Δ Electromagnetic energy = 0

down up

Energy levels in a hydrogen atom

PE

N=1

N=2

N=3

N=4

0

Ionization

UV

Visible light

IR

Average d

i stance from

nu

cle us

PE

PE

PE

“ As the attracting electron gets further from the nucleus the PE goes up”

0= Δ PE + Δ EM energy

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Ionization Level

1st e

Calcium 2, 8, 2

1st Electron …Outermost2nd Electron

3rd Electron

Ionization energy increases as electronscloser to the nucleus are reached.Rise in PE corresponds to more work needed to be done to remove it.

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External Work Done on a Body changes to

Kinetic Energy (macroscopic)Kinetic Energy (microscopic)Potential Energy

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Mechanics1. Work in mechanics (F d) is an usually is an instance where external energy is transferred to a system. 2. Most texts show equations like: Fd = KE or Fd=PE Fd=mgh Fd=1/2mv2

This leads to an incomplete understanding of just what is going on. The equations are really:

External work Fd= mg Δ h and Fd= Δ KE = 1/2 mv22 -1/2 mv1

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3. A system that consistently works in mechanics is:

Work = change in PE + change in KE + heat generated

Fd = Δ PE + Δ KE (macroscopic) + Heat

F Δ d = mg Δ h + (1/2 mv22 -1/2 mv1

2) + heat

F Δ d = mg Δ h + (1/2 mv22 -1/2 mv1

2) + Ffrictiond

Which is the same as 0 = F d + Δ PE + Δ KE + heat

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F Δ d = mg Δ h + (1/2 mv22 - 1/2 mv1

2) + Ffrictiond

0 = ( - ) + (0) - (0) + ( + )

Suppose a 2.0 kg block at rest slides down a frictionless ramp 25 cm high and out on a horizontal surface upon which there was a friction force of 4.0N. Where does the block stop? No external work is done.

Zero = 0 = [(2.0kg)(9.8N/kg)(-0.25m)] + [0 - 0] + [4.0N)(d)] d=+1.23m

Mechanics

Suppose a 2.0 kg block at rest slides down a frictionless ramp 25 cm high and out on a horizontal surface upon which there was a friction force of 4.0N. Where does the block stop? No external work is done.

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Mechanics

Suppose YOU lifted a 3.0kg block vertically upward 9.0 meters and let it slide downan incline upon which the constant force of friction was 15N. What would be thespeed of the block after it had slid a distance of 4.0 meters 15m down the incline anddropped a vertical distance of 3.0 meters? Only consider the starting and ending points involved

F Δ d = mg Δ h + (1/2 mv22 - 1/2 mv1

2) + Ffrictiond

(+) (-) zero (+)

(3.0)(9.8)(+9.0) = (3.0)(9.8)(-3.0) + ( 1/2 (3.0)( v22 ) - ( 0 ) + (15)(4.0)

+265 J = - 88.2J + 1.5 V22 + +60J

V2 = 14 m/s

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The curious example of taking energy from somethingby pushing on it. Applied Force

MotionF•D = Δ PE + Δ KE + heatFrom the dot product we get negative work…which \means we are taking energy out instead of putting it in.

0 = - F•D + Δ PE + Δ KE + heat0 = -[-FD] + 0 + Δ KE + 0

Frictionless4N

KE1 = 40 J

10 m

0= +(4)(10) + KE2 - KE1

0= +40 J + 0 - 40J

40 J of some form of energy must be created from thelost KE; we know we did “work” …in fact as much work is done stopping it as was done getting it going.

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The amount of work we did took energy from the block and therefore that amount of energy must bevented via heat from our bodies. This term does notappear in the equation for the same reason as when we push on a wall and get tired we are actually working on the air….its gaining energy…but this equation can’t be used to “measure” the energy gained by the air. We can calculate the energy gainedby the air in the above case with reason. If you did 40 J of work lifting a rock you would do40 J of work setting it gently back down. In setting itdown the rock loses 40 J of PE and you lose 40 J ofheat….explaining your sense of getting tired.

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Potential Energy changes to

KE (macroscopic)KE (microscopic)Other form of PE

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Electricity: Δ V=IR and EL = IR

V1Q

V2QPE

R

- +

L=length of resistance: HEAT formed

Δ VQ= Δ VIt ELQ=VIt= PE

PE

Ohm’s Law Electric Field

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KE or Heat

Suppose you touch a charged van der graaf at 50,000 volts And 2 x 10 -6 coulomb of charge flows thru your body. How many joules of heat is generated?

V x q = 50,000 j/c x 2 x 10 -6 coul = 1 x 10 -1 j same as a kg falling 1 cm

Electrical PE changes to electron KE which changes into heat.

PE electrical = PE gravitational = same amt of heat formedl

PE + KE electrons = 0KE electrons + KE atoms = 0

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Electricity

A 1.5v battery delivers 0.30amps to a toy car for 5.0 s and the 1.0kg car goes from rest to 2.0 m/s in that time. How much energy is “wasted” as heat?

Change of electrical potential energy is: Δ VIt or( Power x time)

Δ V is really Vlost in all equations using ohm’s law: V=IR

F Δ d = Δ VIt + (1/2 mv22 - 1/2 mv1

2) + Ffrictiond

zero = Vlost I t + 1/2mV22 - 0 + heat

0 = (-1.5)(2.0)(5.0) + (0.5)(1.0)(3.0)2 - 0 + heat 0 = -15J + +4.5J + heat battery lost 15J car gained 4.5J gained heat 10.5J

Fd = Δ PE + Δ KE (macroscopic) + Heat

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The Role of Mass

“The Rest Mass particles have is simply the work done in separating them against their mutual attraction after they arecreated” Richard Feynman

This implies that when particles that attract each other are moved closer and PE goes down…energy must be given offand MASS MUST BE LOST.

In the case of burning a mol of carbon to carbon dioxide the amount of KE (= to loss of PE) is equivalent to 5x10-9g.In normal chemical reactions this mass loss is not measurable.

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Potential Energy changes to

KE (microscopic)

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Binding Energy: The energy required to take apart attracting bodies…Texts: energy “stored” in the atom.

In a Nuclear Reaction enough PEis lost that the mass loss is measurable…unlike chemical reaction.

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Nuclear Fission and Fusion

Fusion: 8 protons + 8 neutrons ------- 1 oxygen nucleus + ENERGYNucleons moving closer together with the attracting Nuclear Force of Attraction

means the PE is going down greatly.. Energy given off is opposite of Binding Energy

The electrostatic PE goes up but the amount of energy is insignificant

Fission: A nucleus splits and becomes pieces whose binding energy is greater.

PE

8 protons

8neutrons

A nucleus

Binding Energy:

Energy required to

take something apart

Exothermic

Individual protona and neutrons

U235

Kr and Ba

BE BE

BE

Exothermic

Going from Lower Binding Energy to Higher

is Exothermic

PEFISSION

235.12517AMU

236.90814 AMU16.12752 AMU

16.0000 AMU

MC2

E=

Even less mass

If a reaction moves toward more binding energy/nucleon then PE may go down and energy must be given off: exothermic

Δ PE + Δ KE =0

down up

Δ

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Nuclear Fusion and The Death of a Star

Nucleons

Hydrogen

Helium

Iron

Heavy elements

Gravitational attraction produces enough heat to begin fusion of H to He in the sun. Actually in the processs ofbeing formed in the collapse of Hatoms the Gravitational PE dropsand a great deal of heat is produced. This heat causes the fusion to take place which produces another dropin PE and even more heat.(physics books refer to Binding Energy per nucleon to “explain” what happens.)When H fuel is expended further collapse of the sunin which PE drops even more produces a great deal more heat and begins the fusion of He to elements up toiron.

When He fuel is gone the sun collapses under the force of gravity and Gravitational PE goes down even more which further raises the temperature BUT the next fusion reaction to heavier elements is endothermic so there is not enough KE to cause fusion…in a sun 100x our sun the collapse continues rapidly and a great burst of heat is given off as the sun core density becomes VERY large….a supernova has produced enough energy tofuse the heavier elements in the periodic chart and incidently produce the mass difference between productsand reactants.

Mass loss

PE

(As gravitationally attractive bodies getcloser together their PE drops.) Δ PE + Δ KE = 0

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Water

PE

Liquid

Solid

When water freezes..attracting bodiesget closer together and PE goes downjust like everything else. However, icefloats. How can the density get less butmolecules get closer together?

The strongest bonding in water is hydrogen bonding…in the process offreezing the bonds involved in hydrogenbonding do get closer together as the same time the average distance betweenmolecules get larger…dispersion forceenergy actually does go up a little.

WATER

Unique properties

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Student questions:1. How does compressing a gas increase PE when molecules are actually getting closer together? Attracting forces are not a factor in increasing gas pressure….work must be done on the gas to compress it.

2. How does compressing a spring increase PE: Moving

atoms either side of their equilibrium position will increase the PE within the solid…attraction results in more PE when its stretched and repulsion results in more PE when compressed.

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www.physchem.infocourtneylantz1@yahoo.com

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