EQ: What does it mean for something to have heat, or be hot? Temperature & Heat

Temperature is related to the average kinetic energy of the particles in a substance. KE = mv2

2

2. SI unit for temp. is the Kelvin

a. K = C + 273 (10C = 283K)

b. C = K – 273 (10K = -263C)

3. Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

The temperature and pressure at which water, water vapor, and ice can coexist in equilibrium.

Physical Standard for Temperature“Kelvin”

Triple Point of Water

Temperature = 0.01CPressure = 4.58 mm Hg

Absolute Zero & the Kelvin ScaleThe Kelvin scale is setup so that its zero point is the coldest possible temperature--absolute zero, at which point a substance would have zero internal energy. This is -273.15 °C, or -459.69 °F.

Absolute zero can never be reached, but there is no limit to how close we can get to it. Scientists have cooled substances to within 10-5 kelvins of absolute zero. How do we know how cold absolute zero is, if nothing has ever been at that temperature? The answer is by graphing Pressure vs. Temperature for a variety of gases and extrapolating.

P

T (°C)

gas A

gas B

gas C

-273.15 °C 0 °C

A gas exerts no pressure when at

absolute zero.

4. Thermal energy relationships

a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).

b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

5. Heat

a. The flow of thermal energy from one object to another.

b. Heat always flows from warmer to cooler objects.

Ice gets warmer while

hand gets cooler

Cup gets cooler while hand gets

warmer

Thermal EquilibriumTwo bodies are said to be at thermal equilibrium if they are at the same temperature. This means there is no net exchange of thermal energy between the two bodies. The top pair of objects are in contact, but since they are at different temps, they are not in thermal equilibrium, and energy is flowing from the hot side to the cold side.

hot coldheat

26 °C 26 °C

No net heat flow

The two purple objects are at the same temp and, therefore are in thermal equilibrium. There is no net flow of heat energy here.

Understanding Heat Transfer, Conduction, Convection and

Radiation

Heat Transfer

• Heat always moves from a warmer place to a cooler place.

• Hot objects in a cooler room will cool to room temperature.

• Cold objects in a warmer room will heat up to room temperature.

Question

• If a cup of coffee and a red popsickle were left on the table in this room what would happen to them? Why?

• The cup of coffee will cool until it reaches room temperature. The popsickle will melt and then the liquid will warm to room temperature.

Heat Transfer Methods

• Heat transfers in three ways:

– Conduction

– Convection

– Radiation

Conduction

When you heat a metal strip at one end, the heat travels to the other end.

As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction

Metals are different

The outer e______ of metal atoms drift, and are free to move.

When the metal is heated, this ‘sea of electrons’ gain k_____ energy and transfer it throughout the metal.

Insulators, such as w___ and p____, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals.

lectrons

inetic

ood lastic

Why does metal feel colder than wood, if they are both at the same temperature?

Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

Convection

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

This effects fluid movement.What is a fluid?A liquid or gas.

Fluid movement

Cooler, more d____, fluids sink through w_____, less dense fluids.

In effect, warmer liquids and gases r___ up.

Cooler liquids and gases s___.

ensearmer

ise

ink

Water movement

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Why is it windy at the seaside?

Cold air sinks

Where is the freezer

compartment put in a fridge?

Freezer compartmen

t

It is put at the top, because cool air sinks, so it cools the food on the way down.

It is warmer at the

bottom, so this warmer

air rises and a

convection current is

set up.

The third method of heat transfer

How does heat energy get from the Sun to the Earth? There are no particles

between the Sun and the Earth so it CANNOT travel by conduction or by convection.

?RADIATION

Radiation

Radiation travels in straight lines

True/False

Radiation can travel through a vacuum

True/False

Radiation requires particles to travel

True/False

Radiation travels at the speed of light

True/False

Emission experiment

Four containers were filled with warm water. Which container would have the warmest water after ten minutes?

Shiny metal

Dull metal

Dull black

Shiny black

The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.

shiny metalradiation

dull blackemitting

Absorption experiment

Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?

The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.

dull blackradiation

shiny metalabsorbing

Shiny metal

Dull metal

Dull black

Shiny black

Convection questions

Why are boilers placed beneath hot water tanks in people’s homes?

Hot water rises.

So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.

Radiation questions

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why are shiny foil blankets wrapped around marathon runners at the end of a race?

The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

1. Which of the following is not a method of heat transfer?

A. Radiation

B. Insulation

C. Conduction

D. Convection

2. In which of the following are the particles closest together?

A. Solid

B. Liquid

C. Gas

D. Fluid

3. How does heat energy reach the Earth from the Sun?

A. Radiation

B. Conduction

C. Convection

D. Insulation

4. Which is the best surface for reflecting heat radiation?

A. Shiny white

B. Dull white

C. Shiny black

D. Dull black

5. Which is the best surface for absorbing heat radiation?

A. Shiny white

B. Dull white

C. Shiny black

D. Dull black

31

Chapter 8 Energy and Matter

2.3Temperature Conversions

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

32

Temperature

Temperature

• is a measure of how hot or cold an object is compared to another object.

• indicates that heat flows from the object with a higher temperature to the object with a lower temperature.

• is measured using a thermometer.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

33

Temperature Scales

Temperature Scales

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

• are Fahrenheit, Celsius, and Kelvin.

• have reference points for the boiling and freezing points of water.

34

A. What is the temperature of freezing water?

1) 0°F 2) 0°C 3) 0 K

B. What is the temperature of boiling water?

1) 100°F 2) 32°F 3) 373 K

C. How many Celsius units are between the boiling and freezing points of water?

1) 100 2) 180 3) 273

Learning Check

35

A. What is the temperature of freezing water?

2) 0°C

B. What is the temperature of boiling water?

3) 373 K

C. How many Celsius units are between the boiling and freezing points of water?

1) 100

Solution

36

• On the Fahrenheit scale, there are 180°F between the freezing and boiling points and on the Celsius scale, there are 100°C.

180°F = 9°F = 1.8°F 100°C 5°C 1°C

• In the formula for the Fahrenheit temperature, adding 32 adjusts the zero point of water from 0°C to 32°F.

TF = 9/5 TC + 32

or

TF = 1.8 TC + 32

Fahrenheit Formula

37

• TC is obtained by rearranging the equation for TF.

TF = 1.8TC + 32

• Subtract 32 from both sides.

TF - 32 = 1.8TC ( +32 - 32)

TF - 32 = 1.8TC

• Divide by 1.8 = °F - 32 = 1.8 TC

1.8 1.8

TF - 32 = TC

1.8

Celsius Formula

38

Solving A Temperature Problem

A person with hypothermia has abody temperature of 34.8°C. What is that temperature in °F?

TF = 1.8 TC + 32

TF = 1.8 (34.8°C) + 32° exact tenth's exact

= 62.6 + 32° = 94.6°F tenth’s Copyright © 2005 by Pearson Education, Inc.

Publishing as Benjamin Cummings

39

The normal temperature of a chickadee is 105.8°F. What is that temperature on the Celsius scale?

1) 73.8°C

2) 58.8°C

3) 41.0°C

Learning Check

40

3) 41.0 °C

TC = (TF - 32°) 1.8

= (105.8 - 32°) 1.8

= 73.8°F = 41.0°C 1.8°

Solution

41

A pepperoni pizza is baked at 455°F. What temperature is needed on the Celsius scale?

1) 423°C

2) 235°C

3) 221°C

Learning Check

42

A pepperoni pizza is baked at 455°F. What temperature is needed on the Celsius scale?

2) 235°C

TF - 32° = TC 1.8

(455 - 32°) = 235°C 1.8

Solution

43

On a cold winter day, the temperature is –15°C.What is that temperature in °F?

1) 19°F

2) 59°F

3) 5°F

Learning Check

44

3) 5°F

TF = 1.8 TC + 32

TF = 1.8(–15°C) + 32°= – 27 + 32°= 5°F

Note: Be sure to use the change sign key on your calculator to enter the minus – sign. 1.8 x 15 +/ – = –27

Solution

45

The Kelvin temperature scale• has 100 units between the freezing and boiling points of

water. 100 K = 100°C or 1 K = 1°C

• is obtained by adding 273 to the Celsius temperature.

TK = TC + 273

• contains the lowest possible temperature, absolute zero (0 K).

0 K = –273°C

Kelvin Temperature Scale

46

TemperaturesTABLE 2.5

47

What is normal body temperature of 37°C in Kelvins?

1) 236 K

2) 310. K

3) 342 K

Learning Check

48

What is normal body temperature of 37°C in kelvins?

2) 310. K

TK = TC + 273

= 37°C + 273

= 310. K

Solution

Specific Heat

a. Some things heat up or cool down faster than others.

Land heats up and cools down faster than water

b. Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K).

1) C water = 4184 J / kg C

2) C sand = 664 J / kg C

This is why land heats up quickly during the day and cools quickly at night and why water

takes longer.

Why does water have such a high specific heat?

Water molecules form strong bonds with each other; therefore it takes more heat energy to

break them. Metals have weak bonds and do not need as much energy to break them.

water metal

How to calculate changes in thermal energy

Q = m x T x Cp

Q = change in thermal energy

m = mass of substance

T = change in temperature (Tf – Ti)

Cp = specific heat of substance

Q = mCpΔT

c. A calorimeter is used to help measure the specific heat of a substance.

First, mass and temperature of water are

measured

Then heated sample is put inside and heat

flows into water

This gives the heat lost by the substance

Knowing its Q value, its mass, and its T, its Cp can

be calculated

T is measured for water to help get its heat gain

Q = mCpΔT

Pause for a Cause:Determine the specific heat of water if 8.8 x 105 Joules are lost when 3.00 Kg of water is cooled from 80.0C to 10.0C.

Answer: 4190J Kg ºC

Cp = __Q__ mΔT

Q = mCpΔT

Pause for a Cause:A metal bolt with a mass of 8.50 x 10-2 kg and a temperature of 85.0 ˚C is placed in a container of water. The mass of the water is 0.150 kg, and its temperature is 25.0˚C. What is the specific heat capacity of the bolt if the final temperature of the bolt and water is 28.4˚C? (c = 4186 J/kg*˚C)

= 2134.86 J

Cp = __Q__ mΔT

Boltmb= 8.50 x 10-2 kgTi = 85.0 x ˚C Tf = 28.4˚CCp = ?

Watermw= 0.150 kgTi = 25.0 x ˚C Tf = 28.4˚CCp = 4186 J/kg*˚C

Q = 0.15Kg * 4186 J (28.4 ˚C – 25 ˚C) Kg ˚C

Cp = ______2134.86 J__________ 8.5x10-2 Kg (28.4 ˚C – 85.0 ˚C)

= 443 J Kg ˚C

Qm = Qc

Pause for a Cause:Find the final equilibrium temperature when 10.0 g of milk at 10.0 ˚ C is added to 1.60 x 102 g of coffee with a temperature of 90.0 ˚C. Assume the specific heats of coffee and milk are the same as for water (c = 4.19 J/g* ˚C), and disregard the heat capacity of the container.

Coffeemc= 1.60 x 102 kgTi = 90.0 ˚C Tf = ?Cpc = = 4.186 J/g*˚C

Milkmm= 10.0gTi = 10.0 ˚C Tf = ?Cpm = 4.186 J/g*˚C CpmmΔT = -CpcmΔT

Q = CpmΔT

Cpmm(tf - ti) = -Cpcm(tf - ti)

Cpm = Cpc

Cpmm(tf - ti) = Cpcm(-tf + ti)

Milkmm= 10.0gTi = 10.0 ˚C Tf = ?Cpm = 4.186 J/g*˚C

Cpmmm(tf - tm) = Cpcmc(-tf + tc)Cpm = Cpc

mm(tf - tm) = mc (-tf + tc)

Solve for tf

mm + mmtm mm

+ mmtm

tf = -mctf + mctc + mmtm

+ mm

mmtf - mmtm = -mctf + mctc

+mctf

mctf +mc mc

tf = mctc + mmtm

mc + mm

Coffeemc= 1.60 x 102 kgTi = 90.0 ˚C Tf = ?Cpc = = 4.186 J/g*˚C

Milkmm= 10.0gTi = 10.0 ˚C Tf = ?Cpm = 4.186 J/g*˚C

Solve for tf

tf = mctc + mmtm

mc + mm tf = (1.60 x 102 g * 90.0 ˚C) + (10.0g * 10.0 ˚C) (1.60 x 102 g + 10.0g)

Coffeemc= 1.60 x 102 gTi = 90.0 ˚C Tf = ?Cpc = = 4.186 J/g*˚C

tf = 14400 g ˚C + 100g ˚C 170 g

tf = 14500 g ˚C 170 g

= 85.3 ˚C

Thermal Expansion of Solids and Liquids

• Thermal expansion of an object is a consequence of the change in the average separation between its atoms or molecules due to the increase of kinetic energy (heat).

Determining Thermal Expansion

Δl = (lf – li) Final length - initial length

α = coefficient of thermal expansion

Li = initial length

Δt = (tf – ti) Final temp - initial temp

Δl = α liΔt

Coefficient of Expansion

• Thermal expansion depends on the material being heated or cooled.

• The coefficient of thermal expansion is determined experimentally.

Pause for a Cause• A steel railroad track has a length of 30.000m when

the temperature is 0˚C. Determine the coefficient of thermal expansion for steel if the tracks expand to 30.013m after a hot day when the temperature is 40.0 ˚C. α = (lf – li)

li(tf – ti)

α = (30.013m – 30.000m)= 30.000m(40.0˚C– 0˚C)

1.08 x 10-6 ˚C-1

Pause for a Cause• A copper bar changes in length by 1.1 meters with

a 150 degree Celsius change in temperature. What is the bar’s original length?

Δl = α liΔt

li = _Δl_

α Δt

li = _______1.1m_____ = 431.4m

(17.0E-6 ˚C-1)(150˚C) li = ˚C m

˚C

Latent Heat & Phase Change• A transfer of heat energy from one

substance to another does not always result in a temperature change.

• For instance, ice water on a hot summer day will remain 0˚ C until all of the ice has melted before the temperature begins to rise

• i.e. energy is lost due to phase change

Latent Heat & Phase Change• The energy needed to change the phase of a given pure

substance is called Latent heat.

• It is dependant on the nature of the substance and the phase change.

solid liquid liquid gas

333,000J/Kg 2,263,300J/Kg

Q = mL

Q = heat (J)m = mass (Kg)L = latent heat (J/Kg)

Latent Heat & Phase ChangeLatent heat of Fusion: melting or freezing

Q = mLf

Latent heat of Vaporization: boiling or condensationQ = mLv

•Latent heat is an experimental value– Dependent on inter & intermolecular forces

Latent Heat of Water

Pause for a Cause:How much heat must be added to a 25g ice cube at 0ºC to change it to water at 0ºC if the latent heat of fusion for water is 3.33 X 10-5J/Kg? Q = mLf

Q = 25g * 1Kg * 3.33 X 105J 1000g * Kg

= 8.3 X 103J