Temperature Energy and Heat - Mrs. Neill's Classesbhsneill.weebly.com › uploads › 3 › 9 › 0...

CHAPTER 3

Temperature

Energy and

Heat

3.1 Temperature

2 3.1 Temperature

• What is temperature?

• Why is temperature important in chemistry?

• How is energy related to temperature?

3 3.1 Temperature

At room temperature, atoms and

molecules are in constant motion

Brownian motion

Milk fat particles are

being pushed around

by water molecules

4 3.1 Temperature

Grains of sand stand still…

… but the individual atoms are

in constant, random motion.

kinetic energy: the energy of motion.

temperature: a measure of the average kinetic energy of

atoms or molecules.

5 3.1 Temperature

Temperature is the measure of

the average kinetic energy of

atoms or molecules, thus as ke

increases so does the

temperature.

Some molecules have more kinetic

energy than the average.

Some molecules have less kinetic

energy than the average.

Temperature is an average

6 3.1 Temperature

Temperature scales

7 3.1 Temperature

Water boils

Water freezes

How can we go back and forth between the two scales?

Temperature scales

8 3.1 Temperature

Asked: Temperature in oC

Given: 100oF

Relationships:

Solve:

Answer: 100oF is the same temperature as 37.8oC

5

329

C FT T

5 5

100 32 689

37.89

o

C CT

What temperature in Celsius is the same as 100oF?

9 3.1 Temperature

Asked: Temperature in oF

Given: 15oC

Relationships:

Solve:

Answer: 15oC is the same temperature as 59oF.

532

9F cT T

5

15 32 27 329

59oFT F

What is the Fahrenheit equivalent of 15oC?

10 3.1 Temperature

All thermometers are based on a physical property that

changes with temperature.

Thermal expansion:

- Mercury thermometers

- Alcohol thermometers

Electrical sensors:

- Thermistor

- Thermocouple

11 3.1 Temperature

Thermal expansion:

- Mercury thermometers

- Alcohol thermometers

Electrical sensors:

- Thermistor

- Thermocouple

The temperature probe

in the Lab-Master uses

a thermistor

All thermometers are based on a physical property that

changes with temperature.

12 3.1 Temperature

kinetic energy: the energy of motion.

temperature: a measure of the average kinetic energy of

atoms or molecules.

heat: thermal energy, the total energy in random

molecular motion, energy resulting from temperature

13 3.1 Temperature

Temperature

While temperature is related to thermal energy, there is no absolute

correlation between the amount of thermal energy (heat) of an object

and its temperature. Temperature measures the concentration of

thermal energy in an object in much the same way that density

measures the concentration of matter in an object. As a result, a large

object will have a much lower temperature than a small object with the

same amount of thermal energy. Different materials respond to

changes in thermal energy with more or less dramatic changes in

temperature.

The temperature of a material is a measure of the average kinetic

energy of the molecules that make up that material. Absolute zero is

defined as the temperature at which the molecules have zero kinetic

energy, which is why it is impossible for anything to be colder.

14 3.1 Temperature

Heat

Heat is a measure of how much

thermal energy is transmitted from

one body to another. We cannot say

a body “has” a certain amount of heat

any more than we can say a body

“has” a certain amount of work. While

both work and heat can be measured

in terms of joules, they are not

measures of energy but rather of

energy transfer. A hot water bottle

has a certain amount of thermal

energy; when you cuddle up with a

hot water bottle, it transmits a certain

amount of heat to your body.

15 3.1 Temperature

Absolute zero

At absolute zero the

kinetic energy is

essentially zero.

3 different scales

16 3.1 Temperature

+ 273

- 273

273Kelvin CelsiusT T

Unit conversion

17 3.1 Temperature

Convert 27oC into kelvins.

Asked: Temperature in kelvin

Given: 27oC

Relationships:

Solve:

Answer: 300 K is the same temperature as 27oC.


27 273 300KT K

Unit conversion

18 3.1 Temperature

932

5Fahrenheit CelsiusT T

5

329

Celsius FahrenheitT T


Molecules are in constant,

random motion.

This affects temperature.

Three temperature scales:

19 3.1 Temperature

CHAPTER 3

3.2 Heat and

Thermal Energy

Temperature Energy and Heat

20 3.1 Temperature

We know now

that heat is

not the same

thing as

temperature.

Measured in oF, oC, K

Measured in… ?

21 3.1 Temperature

Heat can be measured in joules (J).

The joule is the fundamental SI unit of energy and heat.

22 3.1 Temperature

Heat can be measured in calories.

It takes 1 calorie to raise 1 g of water by 1oC.

1 Calorie = 1 kilocalorie = 1,000 calories

23 3.1 Temperature

Heat can be measured in British thermal units (BTU).

24 3.1 Temperature

joules (J)

calories

British thermal units (BTU)

Heat can be measured in

1 calorie = 4.184 joules

1 BTU = 1,055 joules

25 3.1 Temperature

second law of thermodynamics: energy (heat)

spontaneously flows from higher temperature to lower

temperature.

26 3.1 Temperature

Thermal equilibrium

A condition where the temperatures are the same

and heat no longer flows from one material to

another.

Humans are most comfortable at 25*C because the rate of heat flow out of the body matches the rate at which the body generates heat.

Temperatures below 25*C

will feel cold because the

body loses heat too quickly

Temperatures above 25*C

will feel hot because the

body will retain heat rather

than lose it.

27 3.1 Temperature

SURROUNDING

Matter and energy flow

through the system

Only energy can flow

through the system.

Neither matter nor

energy can be

exchanged or flow.

28 3.1 Temperature

first law of thermodynamics:

energy can neither be created

nor destroyed.

29 3.1 Temperature

The energy inside an isolated

system is constant.

The energy lost by a system

must be gained by the surroundings or another system.

first law of thermodynamics: energy can neither be created nor

destroyed.

30 3.1 Temperature

What happens when hot and cold water are not

allowed to mix but are allowed to exchange energy?

Does one side stay hot and one side stays cold?

31 3.1 Temperature

Thermal equilibrium

The system reaches

thermal equilibrium at

45*C

Since both sides have the

same mass of water,

they will reach equilibrium

at the average of the two

temperatures.

80 + 10 = 45

2

32 3.1 Temperature

Specific heat of water:

4.184 J/(g·oC)

Specific heat of gold:

0.129 J/(g·oC)

specific heat: the quantity of energy it takes per gram of a

certain material to raise the temperature by one degree Celsius.

33 3.1 Temperature

One reason is:

Why do different metals have different specific heats?

Ag = 107.87 g/mol Al = 26.98 g/mol

34 3.1 Temperature

A metal-working process needs to heat steel from room

temperature (20oC) to 2,000oC. If the mass of steel is

100 g, how much heat is required?

A table is located on page 83 that lists the specific heat

of common substances.

35 3.1 Temperature

36 3.1 Temperature

A metal-working process needs to heat steel from room

temperature (20oC) to 2,000oC. If the mass of steel is

100 g, how much heat is required?

Asked: Quantity of heat

Given: 100 g of steel,

temperature difference is 2,000oC – 20oC

Relationships:

Solve:

Answer: It takes 93,060 joules to raise the temperature of 100 g of

steel to 2,000oC, assuming no heat gets lost during the

process (which is not a very good assumption!).

0.470 opc J g C

2 1pE mc T T

100 0.470 200 2 93,00 60oE g J g JC

37 3.1 Temperature

Asked: Temperature change in oC

Given: 300 g of water [cp = 4.184 J/(g·oC)], change of 60oC (80oC – 20oC),

and 100,000 g of air [cp = 1.006 J/(g·oC)]

Relationships:

Solve:

Answer: The air in the room gets warmer by about 0.75oC.

2 1pE mc T T

300 4.184 60 75,312

0.75

7

75,312

100,000 1.006

5,312

o

o

o

oEnergy lost by the water g J g C C J

Energy gained by the air energ

JTem

y lost by wa

perature change of airg

te

J g CC

r J

A mass of 300 grams of water at 80oC cools down to 20oC. Assume all the

heat from the water is absorbed by 100 m3 of air (a small room) with a

mass of 100,000 g. What is the temperature change in the air?

*** NOT on test….woohoo

38 3.1 Temperature

conduction: the flow of heat energy through the direct

contact of matter.

39 3.1 Temperature

Would you describe the glass of the test tube as a

thermal conductor or a thermal insulator?

Thermal equilibrium was reached (60oC both inside and outside the test

tube). Because the test tube allowed heat to flow, it is a thermal conductor.

40 3.1 Temperature

Would you describe the styrofoam cup of the test tube

as a thermal conductor or a thermal insulator?

41 3.1 Temperature

Temperature is measured in: oF, oC, kelvin

Heat is measured in: joules (J), calories, British thermal units (BTU)

first law of thermodynamics: energy can neither be created

nor destroyed.

second law of thermodynamics: energy (heat) spontaneously

flows from higher temperature to lower temperature.

42 3.1 Temperature

CHAPTER 3

Temperature

Energy and

Heat3.3 Phase Changes

43 3.1 Temperature

44 3.1 Temperature

Kelvin Scale

The Bose-Einstein state of

matter was the only one

created while your parents

were alive. In 1995, two

scientists, Cornell and

Weiman, finally created the

condensate.

Physicists acknowledge they can never

reach the coldest conceivable

temperature, known as absolute zero

and long ago calculated to be minus

459.67°F. To physicists, temperature is a

measure of how fast atoms are moving,

a reflection of their energy—and

absolute zero is the point at which there

is absolutely no heat energy remaining

to be extracted from a substance.

45 3.1 Temperature

When you get to a temperature near absolute zero,

something special happens. Atoms begin to clump.

The whole process happens at temperatures within a

few billionths of a degree, so you won't see this at

home. When the temperature becomes that low, the

atomic parts can't move at all. They lose almost all of

their energy.

Since there is no more energy to transfer (as in solids

or liquids), all of the atoms have exactly the same

levels, like twins. The result of this clumping is the

BEC. The group of rubidium atoms sits in the same

place, creating a "super atom." There are no longer

thousands of separate atoms. They all take on the

same qualities and, for our purposes, become one

blob.

46 3.1 Temperature

ScienceCasts- The Coolest

Spot in the Universe

47 3.1 Temperature

Where do the drops of water on

the cold window come from?

Is this water?

48 3.1 Temperature

A phase change is a physical change

No chemical

reaction is

involved

Frozen or boiled water molecules

are still water molecules

Melted iron is still iron.

Molecules or atoms are

simply rearranged!

49 3.1 Temperature

Phase changes

50 3.1 Temperature

Melting point Boiling point

Temperature scale

Phase changes

51 3.1 Temperature

How can we move from solid to liquid, and from liquid to gas?

52 3.1 Temperature

How can we move from solid to liquid, and from liquid to gas?

By overcoming the intermolecular forces.

How?

53 3.1 Temperature

Heat of

fusion

Heat of

vaporization

54 3.1 Temperature

Adding more heat may not increase the

temperature during melting or boiling!

55 3.1 Temperature

Heat of

fusion

Heat of

vaporization

∆Hv(joules/gram)

∆Hf(joules/gram)

Add heat to go from solid to liquid, and from liquid to gas.

56 3.1 Temperature

Heat of

fusion

Heat of

vaporization

∆Hv(joules/gram)

∆Hf(joules/gram)

Remove heat to go from gas to liquid, and from liquid to solid.

57 3.1 Temperature

Heat of

fusion

∆Hf (J/g)

Heat of

vaporization∆Hv (J/g)

Overcome

intermolecular

forces

Overcome

intermolecular

forces

58 3.1 Temperature

phase change: a change in the way molecules are

physically arranged in space without chemically changing

the molecules themselves. For example, molecules are

tightly packed together in a liquid and far apart from each

other in a gas.

heat of vaporization, ∆Hv: the energy required to change

the phase of one gram of a material from liquid to gas, or

gas to liquid at constant temperature and constant pressure

at the boiling point.

heat of fusion, ∆Hf: the energy required to change the

phase of one gram of a material from liquid to solid or solid

to liquid at constant temperature and constant pressure at

the melting point.

59 3.1 Temperature

• ENERGY CAN BE RELEASED OR ABSORBED DURING PHASE CHANGES!!!

Energy expended during a phase change MUST be conserved

and is no longer available to change the temperature of the

system!!!

60 3.1 Temperature

Ice cubes with a temperature of –25oC are used to

cool off a glass of punch. Which absorbs more heat:

warming up the ice or melting the ice into water?

The specific heat of ice is 2.0 J/(g·oC).

61 3.1 Temperature





Asked: Which absorbs more heat, warming ice by 25oC or melting it?

Given: The ice starts at –25oC. The specific heat of ice is 2.0 J/(g·oC).

∆Hf(water) = 335 J

Relationships: E = mcp(T2 – T1) and E = m∆Hf

62 3.1 Temperature









Solve: First, let’s calculate the energy that it takes to warm up a gram of

ice from –25oC to 0oC.

So it takes 50 J to warm up 1 g of ice from –25oC to 0oC. The same

gram of ice takes 335 J to melt into liquid water.

2 1 501 2.0 25o opE mc T T g J g C JC

63 3.1 Temperature





Solve: First, let’s calculate the energy that it takes to warm up a gram of

ice from –25oC to 0oC.

So it takes 50 J to warm up 1 g of ice from –25oC to 0oC. The same

gram of ice takes 335 J to melt into liquid water.





Answer: Changing phase (melting) absorbs 335 J per gram of ice but

warming the ice only absorbs 50 J/g. The phase change is

responsible for most of ice’s cooling effect on drinks!

2 1 501 2.0 25o opE mc T T g J g C JC

64 3.1 Temperature

Where did the coffee go?

You left a cup of coffee in your warm room, then took off for the weekend.

Did someone finish your coffee while you were away?

65 3.1 Temperature

evaporation: a phase change from liquid to gas at a

temperature below the boiling point.

66 3.1 Temperature

Is the glass

“sweating”?

Where does the water on

the outside of the glass

come from?

67 3.1 Temperature

Heat of

vaporization

Water molecules in the air (gas) lose energy when in contact with the

cold glass. This loss in thermal energy causes a phase change.

68 3.1 Temperature

Where do the drops of water on

the cold window come from?

Is this water?

69 3.1 Temperature

condensation: a phase change from gas to liquid;

a substance in its gas phase may condense at a

temperature below its boiling point.

latent heat: thermal energy that is absorbed or released

during a phase change.

70 3.1 Temperature

Why?

In Denver, Colorado, water boils at 95oC (203oF) instead of

the usual 100oC (212oF).

71 3.1 Temperature

In Denver, Colorado, water boils at 95oC (203oF) instead of

the usual 100oC (212oF).

72 3.1 Temperature

Phase equilibrium diagram of water

A phase equilibrium diagram shows the relationship between temperature and

pressure and the resulting phase of matter!

Melting

point

Freezing

point

73 3.1 Temperature

74 3.1 Temperature

Sublimation is the phase change as a substance changes from a solid to

a gas without passing through the intermediate state of a liquid.

· Deposition is the phase change as a substance changes from a gas to a

solid without passing through the intermediate state of a liquid.

· TRIPLE POINT - The temperature and pressure at which the solid,

liquid, and gas phases exist simultaneously.

· CRITICAL POINT – The temperature above which a substance will always be a

gas regardless of the pressure.

· NOTE:

o The solid phase is more dense than the liquid phase. (EXCEPTION WATER)

o The line between the solid and gas phases is the equilibrium of solid and gas

phases at that specific pressure and temperature, i.e. a curve of all the

deposition/sublimation points.

o The line between the solid and liquid phases is the equilibrium of solid and

liquid phases at that specific pressure and temperature, i.e. a curve of all the

freezing/melting points.

o The line between the liquid and gas phases is the equilibrium of liquid and gas

phases at that specific pressure and temperature, i.e. a curve of all the

vaporization/condensation points.

75 3.1 Temperature

Triple point

TRIPLE POINT = the temperature and pressure where the solid, liquid and

gas can all coexist in equilibrium……WOW….

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