Thermodynamics

Day 1

Section 1 Notes: Temperature Scales and Conversions

Intro Question

1. How does a thermometer determine temperature?

Thermodynamics (Unit 1 spring)

• Thermodynamics- Physics that deals with heat and its conversion into other forms of energy.

Video Clip: The Thermometer

• 1:36

Video Clip: Fahrenheit and Celsius Scales• 5:14

Temperature Variables

• TK= Temperature Kelvin

• TC= Temperature Celsius

• TF= Temperature Fahrenheit

Video: Absolute Zero

• 1:49

• Absolute Zero= 0 Kelvin, a temperature where no motion would occur. There is no kinetic energy in the molecules.

• 0 Kelvin= -273.15 ºCelsius

Conversion Scale

( )

Example 1

• A healthy person has an oral temperature of 98.6 ºF. What would this reading be on the Celsius scale?

Example 1

• A healthy person has an oral temperature of 98.6 ºF. What would this reading be on the Celsius scale?

Example 2

• A time and temperature sign on a bank indicates the outdoor temperature is -20.0 ºC. What is the corresponding temperature on the Fahrenheit scale?

Example 2

• A time and temperature sign on a blank indicates the outdoor temperature is -20.0 ºC. What is the corresponding temperature on the Fahrenheit scale?

The Kelvin Temperature Scale• Has scientific significance

due to its absolute zero point.

• Has equal divisions as the Celsius scale

• Not written in degrees• 0º C is 273.15 K• Therefore the conversion is:

• CP: – Finish Worksheet Problems 1-4

• Honors: – Finish Worksheet Problems 1-4

Day 2

Intro

1. Convert 50º F into ºC and Kelvin

Intro

1. Convert 50º F into ºC and Kelvin

Intro

1. Convert 50º F into ºC and Kelvin

Video: Voyage up the Celsius Scale• 11:09

Section 2 Notes:Kinetic Energy and Temperature

• Kinetic energy (KE)- Energy of movement

• Temperature- A measure proportional to the average kinetic energy of a substance.

– higher temperature = higher kinetic energy– The more kinetic energy the quicker the molecules are

moving around

Click on the diagram to be taken to the page

• Draw a picture representing molecular motion of three identical molecules at these two temperatures

• Draw a picture representing molecular motion of three identical molecules at these two temperatures

Section 3 Notes: Internal Energy vs. Heat

• Internal energy (U)- Sum of the molecular energy– kinetic energy, potential energy, and all other energies

in the molecules of a substance. – Unit: Joule

• Heat (Q) is energy in transit– energy flows from a hot to a cold substance.– Unit: Joule

• An object never has “heat” or “work” only internal energy (heat is transferred and work is done)

Heat is energy in transit

• Heat lost by one object equals heat gained by another

• Heat lost = Heat gained• -QA = QB

Heat transfers from hot to cold

(a) Holding a hot cup

(b) Holding a cold glass (heat leaving your hand feels cold)

• The coffee looses 468J of heat. How much heat does Bob gain? (assuming no heat was lost to the surroundings)

• The same: Bob gained 468 J of heat

Example 3

– Direction: From high temperature to low temperature

– Rate of transfer depends on temperature difference: The greater temperature difference the greater the energy transfer

Twater =

20º C

Tcan =

15º C

Twater =

35º C

Tcan =

5º C

Example 4

Where would the greater energy transfer take place and which way would the energy transfer?

A. Ice = 0 ºC Juice = 20 ºC

B. Ice = 0 ºC Juice = 25 ºC

B. has a bigger temperature difference and therefore greater energy transfer. Energy transfers from hot to cold: Juice to Ice

What happens when the temperature inside and out are equal?

Twater =

11º C

Tcan =

11º C

• Heat is transferred until there is thermal equilibrium

• Thermal Equilibrium- When temperatures are equal and there is an even exchange of heat

Twater =

11º C

Tcan =

11º C

Section 4 Notes: Heat Transfer

• Types of Heat Transfer:

– Conduction– Convection– Radiation

• Conduction- Caused by vibrating molecules transferring their energy to nearby molecules. Not an actual flow of molecules.

heat transfer

• Thermal conductors- rapidly transfer energy as heat

• Thermal insulators- slowly transfer energy as heat

Challenge

• Put the following in order of most thermally conductive to least.

Copper, Wood, Air, Water, Concrete

12345

1. Copper

2 Concrete

3. Water

4. Wood

5. Air

• Convection- process in which heat is carried from place to place by the bulk movement of a fluid (gas or liquid).

• Examples

• Radiation (electromagnetic radiation) – Reduce internal energy by giving off electromagnetic radiation of particular wavelengths or heated by an absorption of wavelengths.

• Ex. The UV radiation from the

sun making something hot. Absorption

depends on the material.

Draw your own pictures in the table that represent these three types of heat transfer.

Draw your own pictures in the table that represent these three types of heat transfer.

CW

• Finish questions 5 and 6 on the worksheet

Heat Video if time allows

Day 3

Intro

• Intro question/activity:– Draw these two tables in your intro section. In (a) represent the

motion of three identical molecules at these two temperatures. In (b) draw a picture representing these three types of heat transfer. Try not to look at your notes until you are done.

(a) (b)

Intro

• Draw a picture representing molecular motion of three identical molecules at these two temperatures

Intro

Draw your own pictures in the table that represent these three types of heat transfer.

Section 5: Laws of Thermodynamics

A System

• System- A collection of objects upon which attention is being focused on.

• This system includes the flask, water and steam, balloon, and flame.

• Surroundings- everything else

in the environment

The system and surrounding are

separated by walls of some kind.

System

Surroundings

Walls between a system and the outside

• Adiabatic walls- perfectly insulating walls. No heat flow between system and surroundings.

In a system: How can you measure the quantity of heat entering or leaving?

Q = Δ U or Q = Uf – U0

• Q: The quantity of heat that enters or leaves a system• U0: Initial internal energy in system• Uf: Final internal energy in system

• If Q is positive then energy entered the system• If Q is negative then energy left the system

• This is directly related to temperature. – If the system gets colder then heat left– If the system gets warmer then heat entered

Example 5

• The internal energy of the substance is 50 J before

• The internal energy of the substance is 145 J after

a) How much heat was transferred in this system? b) Did it enter or leave?

• First Law of Thermodynamics:

– Conservation of energy applied to thermal systems.

– Energy can neither be created nor destroyed. It can only change forms

– Stated in an equation

ΔU = Q + W

First Law of Thermodynamics: Conservation of Energy

ΔU = Q + W

– Internal Energy (U) • (positive if internal energy is gained)

– Heat (Q) • (positive if heat is transferred in)

– Work (W)

• (positive if work is done on the system)

– The unit for all of these is the Joule (J)

Example 6 & 7

6. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy?

7. A system gains 1500 of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?

6. A system gains 1500 J of heat from its surroundings, and 2200 J of work is done by the system on the surroundings. What is the change in internal energy?

7. A system gains 1500 of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?

1500 - 2200

1500 + 2200

Example 6 & 7

Now how can you tell if work is done by or on a system?

Is work done on or by the system ?a) nail/wood system b) Bunsen burner,

flask, balloon system

• Work is done by the man causing frictional forces between the nail and the wood fiber.

• Work increases the internal energy of the wood and nail.

Work done on a system:Work to Internal Energy

Work done by a system:Internal Energy to Work

• The balloon expands doing work on its surroundings

• The expanding balloon pushes the air away

Work done on or by a gas

• Volume must change or no work is done.

• On a gas- Volume decreases (work must be done to force molecules into a smaller area)

• By a gas- Volume increases (the pressure of the gas causes the volume to increase)

Section 5 Notes

4 Common Thermal Processes• Isobaric Process • Isochoric process (isovolumetric)• Isothermal process • Adiabatic process

• Each will have their own assumptions

4 Thermal Processes

• Isobaric Process – occurs at constant pressure

• ΔP = 0

4 Thermal Processes

• Isochoric process (Isovolumetric) – one that occurs at constant volume.

• ΔV = 0 and therefore W = 0

Thermal Processes

• Isothermal process – one that occurs at constant temperature

• T (temperature) directly relates to U (internal energy)

• ΔU = 0

Thermal Processes

• Adiabatic process – on that occurs with no transfer of heat

• ΔQ = 0

Look for these terms in questions since they assume givens

• Isobaric Process ΔP = 0• Isochoric process ΔW = 0• Isothermal process ΔU = 0• Adiabatic process ΔQ = 0

Example 8

• How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?

Example 8

• How much heat has entered or left the system when 500J of work has been done on the system in an isothermal process?

Example 9

• How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?

Example 9

• How much work is done on or by the system when internal energy increases by 55J in n adiabatic process?

CW/HW

• Do the first law of thermodynamics questions 7-10 on the worksheet

• Define the 16 words on the worksheet

Day 4

Intro

1. What does an adiabatic process tell you?

2. What does an isovolumetric process tell you?

3. What does an isothermal process tell you

4. How much work is done on or by the system when internal energy decreases by 45J in an adiabatic process?

5. What is the change in internal energy if 650 J of work is done and 50J of heat is transferred in?

Section 6: Three Laws of Thermodynamics

First Law of Thermodynamics

1. Energy can neither be created nor destroyed

• Energy Conservation: Conservation of energy applied to thermal systems.

• . It can only change forms

• When heat is added to a system, it transforms to an equal amount of some other form of energy.

• Equation:• ΔU = Q + W (work is done on a system)

Second Law of Thermodynamics2. Entropy in a system increases over time. Entropy- Measure of randomness or disorder in a system

This occurs even when a system is left untouched.Other parts of the second law of thermodynamic

• Heat goes from hot to cold.• No cyclic process is 100% efficient • it can’t convert heat entirely into work • Some energy will always be transferred out to

surroundings as heat.

Third Law of Thermodynamics

3. absolute zero cannot be reached

• As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

• A theoretical impossibility– If it occurred everything would stop and there

would be no more entropy

Section 7: Transformation of energy in a heat engine

The Heat Engine– a device that used a difference in temperature of two

substances to do mechanical work – It transferring energy from a high-temperature

substance (the boiler) to a lower temperature substance

– For each complete cycle: Wnet = Qh - Qc

What the variables stand for here:

Qh = Heat from high temperature substance

Qc = Heat to low temperature substance

W or work equals the difference of Qh and Qc

The Heat EngineHow it works: main points

There will be an area of high temperature (boiler) and an area of low temperature

• Heat wants to go from a high temperature to a low temperature.

• Work is done by capturing energy in the transfer and using it to do work

• The work done by the engine equals the difference in heat transferred from the hot to cold substance.

The Heat Engine–For each complete cycle: Work =

Energy transferred as heat from the high temperature substance to the colder temperature substance

What the variables stand for here:

Qh = Heat from high temperature substance

Qc = Heat to low temperature substance

W or work equals the difference of Qh and Qc

Example 10

• A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?

Example 10

• A heat engine is working at 50% efficiency. How much work is done between a 670J and 200J reservoir?

Example 11: (just added and not on your worksheet)Do this question on free space below example 10

A heat engine has a 5000 J reservoir and a 2000J reservoir. If the engine can does 2100J of work, how efficient is it?

•  

•  

•  

Question 1:

Which law of thermodynamics relates to the 5000J and 2000J

reservoir and the direction of heat transfer and not being 100% efficient?

•  

Question 1:

Which law of thermodynamics relates to the 5000J and 2000J

reservoir and the direction of heat transfer and not being 100% efficient?

Second Law of thermodynamics (Entropy)

Nuclear Physics

Intro:

1. What atom is this?

2. Where do you find protons?

3. Where do you find neurons?

4. Where do you find electrons?

5. How many protons does it have?

6. How many neutrons?

7. Is it a neutral atom, and how do you know?

ALL CLASSES MEET IN COMPUTER LAB 1.618 TOMORROW

The Atom

In the nucleus (nucleons)

Proton- (+) charged particle

Neutron- no charge

Outside the nucleus

Electron- (-) charged particle

has almost no mass

Nucleons

• Are particles occupying the nucleus• Consist of + charged protons and neutral

neutrons• Have almost 2000 times the mass of

electrons

• Where can you find the number of protons? • It’s the atomic number (found on the periodic

table)

Nuclear Notation

Atomic number = no. of protons

Atomic mass = protons + neutrons

Atomic number is the same as the number of electrons in an uncharged atom

5

B10.811

Atomic Number

Atomic Mass

1a. How many protons?

1b. How many neutrons?

1c. How many nucleons?

You may see atomic number written many ways. The smaller number is the atomic number and the larger is the atomic mass

Question 1

• has 13 protons and 14 neutrons for a total of 27 nucleons

• has 13 protons and 15 neutrons for a total of 28 nucleons

• The identity of an element depends on the number of protons

2813

Isotopes:

• Atoms of the same element with different numbers of neutrons (different masses)

Most common stable isotope of carbon

Unstable radioactive isotope of carbon

Question 2

• List the four fundamental forces from strongest to weakest

1.

2.

3.

4.

Review of Fundamental forces

Strongest to weakest1. Strong Nuclear Force

2. Electromagnetic Force

3. Weak Nuclear Force

4. Gravity

Forces Acting on Nucleons:

Forces of attraction between nucleons

Strong forces– Are independent of the charge of the nucleon– Are short range (exist only between closest

neighbors)

Electrical force (electrostatic)– Force of repulsions between positively

charged protons– Are long range

When are nuclei unstable? (naturally radioactive)

a. Large nuclei (Z > 82) – electrical forces of repulsion are greater than strong forces of attraction

b. Wrong neutron : proton ratio

stable nucleus no. of protons no. of neutrons

6 6

13 14

26 30

56 81

82 125

When are nuclei unstable?

Bigger atoms require more neutrons per proton to keep the atom stable

A radioactive isotope:

• Has an unstable nucleus

• Spontaneously emits a particle and decays into another element (to become more stable)

Transmutation

• Changing into another element through radioactive decay

Who am I?

• I worked with my husband and discovered radium, a radioactive material

Marie and Pierre Curie

• First to discover that compounds containing uranium emitted penetrating rays.

• Discovered radioactive polonium and radium

Types of Radioactive Emission

Symbol Composition Stopped By

Alpha 2p + 2n (helium)

Paper

Beta 1e (electron)

Aluminum

Gamma γ Energy only

Lead

Use a periodic table for decay equations

Alpha Decay

• Radiation through the loss of 2p + 2n or (helium)

Beta Decay

• Radiation where a neutron splits, giving off an electron and becoming a proton in the new element

Gamma Decay

• A change energy state gives off a gamma particle or photon

Question 3a

Balance the nuclear equation after alpha decay

Question 3a

Balance the nuclear equation after alpha decay

Question 3b

Balance the nuclear equation after beta decay

Remember in beta decay a neutron changes into a proton by giving off an electron

Question 3b

Balance the nuclear equation after beta decay

Remember in beta decay a neutron changes into a proton by giving off an electron

Extra Question

• Which radioactive isotope completes this nuclear decay equation

6

Extra Problem

• Finish off the equation

 

Half Life and Half Life Calculations

• Half Life- time it takes for half of the radioactive sample to decay.– Ranges from a fraction of a

second to billions of years

• Decay constant- Probability per time that a nucleus would decay

CW/HW

• Do Page 1 of the worksheet: Nuclear and Thermodynamics Extra Practice

Section 2 Intro

1. Rewrite and balance the equation above

2. What kind of decay is shown above?

3. What is the particle given off during alpha decay composed of?

4. What is the particle given off during beta decay composed of?

Section 2: Nuclear Physics Math

Half Life Calculations

Draw and finish off the table in your notes

# of Half Lives Fraction Remaining

Fraction Decayed

How much of 100g sample left

How much of 100g sample decayed

0 1.0 0 100g 0

1

2

3

4

5

Half Life and Half Life Calculations

y= fraction of radioactive material left

n= number of half lives

T1/2 = half life time

  

Example A

• How much of the original radioactive material is left after 15 half-lives?

 

Example A

• How much of the original radioactive material is left after 15 half-lives?

 

Not every radioactive isotope is created equal

Parent Decays into: Half life (years)

Carbon-14 Nitrogen-14 5,730

Aluminum-26 Magnesium-26 740,000

Iodine-129 Xenon-129 17 million

Uranium-235 Lead-207 704 million

Potassium-40 Argon-40 1.3 billion

Rubidium-87 Strontium-87 49 billion

Example B

• We start with 400g of a sample, how many grams would remain after 3 half lives?

#1 figure out the fraction remaining (y)

#2 multiply the fraction remaining by the mass of the original sample (y) x (mo)

mo = initial mass of radioactive material

Example B

•  

Example C

• A radioactive sample has a mass of 56 mg and a half life of 30 minutes. How much of the sample remains after 60 minutes have passed?

• Step#1 find number of half lives (n)• Step#2 find what fraction remains (y)• Step#3 if an initial sample was given multiply

fraction remaining (y) x (the initial sample mass)

Example C

• A radioactive sample has a mass of 56 mg and a half life of 30 minutes. How much of the sample remains after 60 minutes have passed?

• Step#1 find number of half lives (n)

   Rearranges to

Example C

• A radioactive sample has a mass of 56 mg and a half life of 30 minutes. How much of the sample remains after 60 minutes have passed?

• Step#1 find number of half lives (n) = 2• Step#2 find what fraction remains (y)

   

Example C• A radioactive sample has a mass of 56 mg

and a half life of 30 minutes. How much of the sample remains after 60 minutes have passed?

• Step#1 find number of half lives (n) = 2• Step#2 find what fraction remains (y) = 0.25

• Step#3 if an initial sample was given multiply fraction remaining (y) x (the initial sample mass)

• 56 x 0.25 = 14 grams

Example D

• An unknown radioactive material has a half life of 4000 years. How much of the sample will remain after 20,000 years?

   Rearranges to

Example D

• An unknown radioactive material has a half life of 4000 years. How much of the sample will remain after 20,000 years?

   Rearranges to

   

Example E•  

Example E•  

(n) Number of half lives

original 1 2 3 4 5

Quantity remaining 32g 16g 8g 4g 2g 1g

Example E•  

(n) Number of half lives

original 1 2 3 4 5

Quantity remaining 32g 16g 8g 4g 2g 1g

2. What is the T1/2

 

Example E•  

(n) Number of half lives

original 1 2 3 4 5

Quantity remaining 32g 16g 8g 4g 2g 1g

2. What is the T1/2 = 18/5

Useful applications of radioactivity• Can be detected and therefore small

amounts can be used as tracers for medical diagnosis

• Larger amounts can be used as treatments for certain types of cancers (cancer cells are killed before healthy cells)

• Can be used to determine the age of rocks and fossils

Show what you know

Types of Nuclear Reactions

Natural transmutation – Uranium spontaneously decays

Artificial transmutation – bombardment of a stable isotope to force it to decay

 

 

Question 4

• Balance the reaction after the following artificial transmutation.

Types of Nuclear Reactions

Artificial transmutation • First done by Earnest Rutherford

• When the bullets are positively charged, they are repelled by the nucleus they are bombarding. To overcome the repulsions, they must be accelerated to very high speeds by particle accelerators.

 

Nuclear Fission

• Nuclear fission - Heavy nuclei are bombarded with neutrons and split.

plus a tremendous amount of energy

Nuclear fission

• Mass of particles produced is slightly less than the mass of the reactants. This mass is converted into energy. (E=mc2)

Nuclear fission is a chain reaction. Neutrons are needed to start and released as a product which can start more reactions.

Critical mass: minimum mass of fissionable material required for a chain reaction.

Problems with Fission• Nuclear fission produces radioactive waste that has

a large half life.

U-235 Uranium 235

– Half life of U-235 is 713 million years

• We cannot get rid of this dangerous product so we store it away from anything it can harm.– We deeply bury

• Meltdown if cooling system fails the reactor can overheat and melt releasing radioactive materials

• Nuclear fusion – combination of small nuclei into larger with release of energy.

• Mass of particles produced is much less than the mass of the reactants.

• This mass is converted into energy. (E=mc2)• Can release up to 10 times that of fission• Occurs naturally in our sun and other stars• Does not give off radioactive waste

Problems with Fusion

• Fusion requires high temperatures like those in the stars.

• We cannot sustain these temperatures without vaporizing the container of the fusion reaction.

• Today many are looking into ways of making fusion work under sustainable conditions