Temperature vs. Heat vs. Internal Energy - PowerPoint Presentation

Slide1

Temperature vs. Heat vs. Internal Energy

Work in groups in 2-3Collect a whiteboard and pensMake a Venn Diagram showing how the terms Temperature, Heat and Internal Energy are similar and differentUse your notes and phones for resources!

Slide2

Heat, Thermal Energy and Internal Energy:Words of caution!

“To describe the energy that a high temperature object has, it is not a correct use of the word heat to say that the object "possesses heat" - it is better to say that it possesses internal energy as a result of its molecular motion. The word heat is better reserved to describe the process of transfer of energy from a high temperature object to a lower temperature one.

Slide3

Thermal Physics

AP Physics B

Slide4

Thermal Physics

Temperature and

Heat

Mechanical equivalent of heat

Zeroth

Law of Thermodynamics

Latent Heat

Heat transfer and thermal expansion

Conduction

Convection

Radiation

Kinetic

Theory

and

Thermodynamics

Ideal gases

Kinetic model

Ideal gas law

Laws of thermodynamics

First law (including processes on

pV

diagrams)

Second law (including heat engines)

Slide5

Temperature and Heat

Temperature

: physical property of matter that quantitatively expresses the common notions of hot and cold.

The temperature varies with the

microscopic speed of the fundamental particles

that it contains (or their kinetic energy).

Slide6

All particles have internal movement... ALWAYS

Temperature measures the average Kinetic Energy of the particles within a substanceNOT the total energy of the substance, which depends on it’s mass

Slide7

Basis for Temp Scales

Fahrenheit

: Oldest scale, Freezing point is 32

o

F, Boiling point 212

o

F ~

makes no sense…

Celsius

: Water Freezes/Melts at 0

o

C, and boils at 100

o

C

Kelvin

: 0

o

K is the coolest theoretical temperature possible, no negative Kelvins. Same increments at Celsius Scale. Basically an updated version of the Celsius scale

Slide8

Slide9

Temperature

Scales:

Slide10

Absolute Zero – 0 Kelvin

Q: What

would have to happen in order to reach

absolute zero

?

Atoms and subatomic particles would have to stop moving… impossible.

2003

- MIT scientists

cooled

sodium gas to the lowest temperature ever recorded -- only half-a-billionth of a degree above absolute zero.

Slide11

Zeroth Law of Thermodynamics

If Tx = Ty and Ty = Tz, then Tx = TzWell … Duh!Why Zeroth Law???? Made after Laws 1,2, and 3

Slide12

Heat

Heat: Transmission of energy from one body to another due to temperature difference (hot to cold) – unit is Calorie or Joule

Slide13

Internal Energy

Compare TOTAL INTERNAL ENERGY of gas to liquid/solidStudy liquids/solids now…ideal gases later

Slide14

Heat

Take Home Message(s)

Heat is a

process

Matter contains internal energy

NOT HEAT

Heat is the transfer or conversion of energy

Compare to Work and Mechanical Energy…

Slide15

In-Class Work + Homework

Collect the worksheet from the front of the room

If you haven’t already

… please watch the Video – 2 for homework! + MC Q’s: 6, 24, 30, 32, 35, 39, 58

ALSO

: Watch Specific Heat Video if you need a review from Phys 11!

Slide16

Heat Transfer Due to ΔT

All materials are not created equally in terms of heat transfer

Would you rather touch your tongue to a 0

o

C

metal pole

or wooden pole?

Why

? (Splinters?)

Slide17

Thermal Conductivity, k

k is a measure of an object’s ability to conduct heat (transfer) – RATE QUANTITYHigher k means faster rate of transferMaterials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulationH – Rate of Heat Transfer (J/s or kcal/s)A – Area of surface in contactL – Thickness

Slide18

Question: Find H of the glass below in J/s

Ans

: 7.9 x 10

2

J/s

Slide19

Question

What is a better insulator, an object with a

larger k

, or

smaller k

?

Slide20

Question

What is a better insulator, an object with a larger k, or smaller k?

Ans

: Smaller k! Some questions are not difficult



Slide21

Question

If air has such a low thermal conductivity (0.22), why do we need to wear clothes? (Other than for decency reasons…)

Slide22

Question

If air has such a low thermal conductivity (0.22), why do we need to wear clothes? (Other than for decency reasons…)ANS: Air is always moving, we use clothes to trap air close to our bodies. The thicker the clothes the more air we trap.

Slide23

Specific Heat: Heat Transfer with Changes in Temperature

Q =

mc∆T

TOTAL Heat

transfer

depends on amount of material (m), temperature difference (∆T), and material property (c)

c

=

specific heat

– amount of heat/mass required to raise temperature by 1 degree

(

K or C!

)

Note

: Specific Heat was covered in Physics

11 as well as AP Chem

Slide24

Water vs. Copper

c

water

= 1

cal

/g

o

C

= 4186 J / kg

o

C

c

copper

= 0.093

cal

/g

o

C

= 389 J / kg

o

C

1 gram of copper at 0

o

C

and 1 gram of water at 0

o

C

If heated by 1

o

C…

.

Slide25

Specific Heat: Heat Transfer with Changes in Temp

∆

T= Q/

mc

Same

Q transfers,

different

objects (

ignore -/+!

)

Big mass

vs

. small mass:

small

mass will get hotter

Metal (lower c) vs. Wood (higher c)

:

metal gets

hotter

Slide26

Hot Object Added to Cool Liquid

ΔQ = 0 (closed system)

Q heat

IN =

Q heat

OUT

Q

Lost =

Q

Gained

In this case….

-

Q

hot

=

Q

cold

-

m

hot

c

hot

(

T

final

-

T

hot

) =

m

cold

c

cold

(

T

final

-T

cold

)

Slide27

Question

500. grams of 20.0o C water is added to 700. g of 85o C water. What is temperature of the mixture?

Slide28

ANSWER

500. grams of 20.0o C water is added to 700. g of 85o C water. What is temperature of the mixture?

Slide29

Question – Connect to AP Chem Lab!

We wish to determine the specific heat of a new alloy. A 0.150 kg sample of the alloy is heated too

540

o

C

.

It is then quickly placed in 400. g of water at

10.0

o

,

which is contained in a 200. g aluminum calorimeter cup. (

Assume that the insulating jacket insulates well, so the temperature does not change significantly

).

The final temperature of the mixture is

30.5

o

C

.

Calculate the specific heat of the alloy

.

c

w

= 4186 J/kg

o

C

;

c

cal

= 900.0 J/kg

o

C

-

m

s

c

s

ΔT

=

m

w

c

w

ΔT

+

m

cal

c

cal

ΔT

Remember,

Heat LOST

=

Heat GAINED

(this changes your ΔT)

Slide30

ANSWER – 497 J/kg oC

We wish to determine the specific heat of a new alloy. A 0.150 kg sample of the alloy is heated too 540o C. It is then quickly placed in 400. g of water at 10.0o , which is contained in a 200. g aluminum calorimeter cup. (Assume that the insulating jacket insulates well, so the temperature does not change significantly). The final temperature of the mixture is 30.5o C. Calculate the specific heat of the alloy.cw = 4186 J/kg oC ; ccal = 900.0 J/kg oC Remember, Heat LOST = Heat GAINED (this changes your ΔT)

Heat gained

Heat lost

Slide31

Phases and Phase Changes

Slide32

Question: Why doesn’t the temp increase at 0o C and 100o C?

Slide33

Energy Input goes to enabling (?!?) the Phase Change

Slide34

Heat Transfer w/out Changes in T (Phase Changes)

If No ∆T

: Phase change

MUST

be occurring

Input of energy is used to break

inter

molecular bonds

Q = m x L

Heat transfer depends on how much (mass), and material property (L)

L =

latent heat

of

fusion

(melting/solidifying) or

vaporization

(vaporizing/condensing)

L

f water

= 3.33x10

5

J/kg

L

v

water

=2.26x10

6

J/kg

Slide35

Total Heat

Go from -50 C to 120 C…

Q

total

= Q

-50-0

+ Q

0

+ Q

0

-100

+ Q

100

+ Q

100

-120

Q

total

= mc(50)

+

mL

f

+

mc(100)

+

mL

v

+

mc(20)

Note

: water and ice have DIFFERENT specific heats!

Slide36

Question

How much energy does a refrigerator have to remove from 1.5 kg of water at 20.0

o

C to make ice at -12

o

C. The Heat of Fusion is 3.33 x10

5

J/Kg, the specific heat of water is 4180 J/(kg

o

C), the specific heat of ice is 2100 J/(kg

o

C).

Slide37

ANSWER

How much energy (in kJ) does a refrigerator have to remove from 1.5 kg of water at 20.0o C to make ice at -12o C. The Heat of Fusion is 3.33 x105 J/Kg, the specific heat of water is 4180 J/(kgoC), the specific heat of ice is 2100 J/(kgoC).

Slide38

Joule’s Experiment - GENIUS

Slide39

Video – Mechanical Equivalent of Heat

Slide40

For the Rest of Class!

Complete the Heat Transfer Worksheet

Heat Transfer – AP Questions: MC: 10, 26, 28, 42, 43, 53, 56, 65, 81

Slide41

Now what…

Next Video

: Ideal Gases

MC Question’s

:

2,5,7,9,21-23,27,31,38,44,45

,

47,48,51,52,61

-

64,73,76,78

Next Class

: Quiz on Ideal Gases + Gas Law Simulation (

Please bring a computer!

)