# Section 1 Notes: Temperature Scales and Conversions

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

Internal Energy vs. Heat
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. 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
Holding a hot cup Holing a cold glass (heat leaving your hand feels cold)

Example 3 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

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? Ice = 0 ºC Juice = 20 ºC 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 =

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 =

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 1 2 3 4 5

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?

ΔU = Q + W 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 of heat, but 2200 J of work is done on the system by the surroundings. What is the change in internal energy?

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

Now how can you tell if work is done by or on a system?
Is work done on or by the system ? nail/wood system b) Bunsen burner, flask, balloon system

Work done on a system: Work to Internal Energy
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 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

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 Engine How 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?