Section 1 Notes: Temperature Scales and Conversions

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.

Temperature Variables

• TK= Temperature Kelvin

• TC= Temperature Celsius

• TF= Temperature Fahrenheit

• 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:

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

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) Holing 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.

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

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?

Section 6: Three Laws of Thermodynamics

First Law of Thermodynamics

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

• Energy can neither be created nor destroyed. 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 Thermodynamics

• (Second Law) Law of Entropy– 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.

– Energy systems have a tendency to increase their entropy or disorder.

• Entropy- Measure of randomness or disorder in a system

Third Law of Thermodynamics

• 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?