Which is the largest unit: one

Celsius degree, one Kelvin

degree, or one Fahrenheit

degree?

1) one Celsius degree

2) one Kelvin degree

3) one Fahrenheit degree

4) both one Celsius degree and one Kelvin degree

5) both one Fahrenheit degree and one Celsius degree

ConcepTest 16.1ConcepTest 16.1 DegreesDegrees

Which is the largest unit: one

Celsius degree, one Kelvin

degree, or one Fahrenheit

degree?

1) one Celsius degree

2) one Kelvin degree

3) one Fahrenheit degree

4) both one Celsius degree and one Kelvin degree

5) both one Fahrenheit degree and one Celsius degree

The Celsius degree and the Kelvin degree are the same size. The scales only differ by an offset, not by the size of the degree unit. For Fahrenheit, there are 180 degrees between boiling and freezing (212°F–32°F). For Celsius, there are 100 degrees between the same points, so the Celsius (and Kelvin) degrees must be larger.

ConcepTest 16.1ConcepTest 16.1 DegreesDegrees

It turns out that – 40°C is the same

temperature as – 40°F. Is there a

temperature at which the Kelvin and

Celsius scales agree?

1) yes, at 0 °C

2) yes, at -273 °C

3) yes, at 0 K

4) no

ConcepTest 16.2ConcepTest 16.2 Freezing ColdFreezing Cold

It turns out that – 40°C is the same

temperature as – 40°F. Is there a

temperature at which the Kelvin and

Celsius scales agree?

1) yes, at 0 °C

2) yes, at -273 °C

3) yes, at 0 K

4) no

The Celsius and Kelvin scales differ only by an offset, which is 273 degrees. Therefore, a temperature on one scale can never match the same numerical value on the other scale. The reason that such agreement is possible for Celsius and Fahrenheit is the fact that the actual degree units have different sizes (recall the previous question).

ConcepTest 16.2ConcepTest 16.2 Freezing ColdFreezing Cold

You may notice that if a

mercury-in-glass thermometer

is inserted into a hot liquid, the

mercury column first drops,

and then later starts to rise (as

you expect). How do you

explain this drop?

1) the mercury contracts before the glass contracts

2) the glass contracts before the mercury contracts

3) the mercury contracts before the glass expands

4) the glass expands before the mercury expands

5) the mercury expands before the glass contracts

ConcepTest 16.3ConcepTest 16.3 ThermometersThermometers

You may notice that if a

mercury-in-glass thermometer

is inserted into a hot liquid, the

mercury column first drops,

and then later starts to rise (as

you expect). How do you

explain this drop?

1) the mercury contracts before the glass contracts

2) the glass contracts before the mercury contracts

3) the mercury contracts before the glass expands

4) the glass expands before the mercury expands

5) the mercury expands before the glass contracts

The hot liquid touches the glass first, so initially the glass expands slightly. This increases the volume inside the glass, and so the mercury level drops slightly. Once the mercury heats up, it begins to expand and then the characteristic rise in the mercury column follows, indicating the increase in temperature that you expected to measure.

ConcepTest 16.3ConcepTest 16.3 ThermometersThermometers

Follow-up:Follow-up: Is it possible to have the mercury first rise and later drop? Is it possible to have the mercury first rise and later drop?

ConcepTest 16.4ConcepTest 16.4 GlassesGlasses

1) run hot water over them both

2) put hot water in the inner one

3) run hot water over the outer one

4) run cold water over them both

5) break the glasses

Two drinking glasses are

stuck, one inside the other.

How would you get them

unstuck?

Running hot water only over the outer glassouter glass will

allow the outer one to expandouter one to expand, while the inner glass

remains relatively unchanged. This should loosen

the outer glass and free it.

ConcepTest 16.4ConcepTest 16.4 GlassesGlasses

1) run hot water over them both

2) put hot water in the inner one

3) run hot water over the outer one

4) run cold water over them both

5) break the glasses

Two drinking glasses are

stuck, one inside the other.

How would you get them

unstuck?

A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected?

1) measured lengths will be too small

2) measured lengths will still be accurate

3) measured lengths will be too big

ConcepTest 16.5aConcepTest 16.5a Steel Expansion ISteel Expansion I

A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected?

1) measured lengths will be too small

2) measured lengths will still be accurate

3) measured lengths will be too big

The tape measure will expand, so its markings will spread out farther than the correct amount. When it is laid down next to an object of fixed length, you will read too few markings for that given length, so the measured length will be too small.

ConcepTest 16.5aConcepTest 16.5a Steel Expansion ISteel Expansion I

1) gets larger

2) gets smaller

3) stays the same

4) vanishes

Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole?

ConcepTest 16.5bConcepTest 16.5b Steel Expansion IISteel Expansion II

1) gets larger

2) gets smaller

3) stays the same

4) vanishes

Imagine drawing a circle on the plate. This circle will expand This circle will expand

outward along with the rest of the outward along with the rest of the

plate.plate. Now replace the circle with the hole, and you can see that the hole will expand outward as well.

Note that the material does Note that the material does NOTNOT

“expand inward” to fill the hole!!“expand inward” to fill the hole!!

expansionexpansion

Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole?

ConcepTest 16.5bConcepTest 16.5b Steel Expansion IISteel Expansion II

ConcepTest 16.6aConcepTest 16.6a Steel Ring ISteel Ring I

Coefficient of volume expansion (1/°C )

Glass HgQuartz Air

AlSteel

1) aluminum

2) steel

3) glass

4) aluminum and steel

5) all three

A steel ring stands on edge with a rod of some material inside. As this system is heated, for which of the following rod materials will the rod eventually touch the top of the ring?

Aluminum Aluminum is the only material that has a larger larger value value than the steel ring, so that means that the aluminum rod will aluminum rod will expand more than steel ringexpand more than steel ring. Thus, only in that case does the rod have a chance of reaching the top of the steel ring.

ConcepTest 16.6aConcepTest 16.6a Steel Ring ISteel Ring I

Coefficient of volume expansion (1/°C )

Glass HgQuartz Air

AlSteel

1) aluminum

2) steel

3) glass

4) aluminum and steel

5) all three

A steel ring stands on edge with a rod of some material inside. As this system is heated, for which of the following rod materials will the rod eventually touch the top of the ring?

ConcepTest 16.6bConcepTest 16.6b Steel Ring IISteel Ring II

Coefficient of volume expansion (1/°C )

Glass HgQuartz

Air

AlSteel

1) heat the thing up

2) cool the thing down

3) blow the thing up

You want to take apart a couple of

aluminum parts held together by

steel screws, but the screws are

stuck. What should you do?

Since aluminum has a larger aluminum has a larger value value, that means aluminum aluminum

expands more than steelexpands more than steel. Thus, by heating the part, the

aluminum holes will expand faster than the steel screwsaluminum holes will expand faster than the steel screws and the

screws will come loose.

ConcepTest 16.6bConcepTest 16.6b Steel Ring IISteel Ring II

Coefficient of volume expansion (1/°C )

Glass HgQuartz

Air

AlSteel

1) heat the thing up

2) cool the thing down

3) blow the thing up

You want to take apart a couple of

aluminum parts held together by

steel screws, but the screws are

stuck. What should you do?

Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change?

1) the one with the higher initial temperature

2) the one with the lower initial temperature

3) the one with the greater mass

4) the one with the smaller mass

5) the one with the higher specific heat

ConcepTest 16.8aConcepTest 16.8a Thermal Contact I Thermal Contact I

Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change?

1) the one with the higher initial temperature

2) the one with the lower initial temperature

3) the one with the greater mass

4) the one with the smaller mass

5) the one with the higher specific heat

Since the objects are made of the same material, the only difference between them is their mass. Clearly, the object with less mass will change temperature more easily since not much material is there (compared to the more massive object).

ConcepTest 16.8aConcepTest 16.8a Thermal Contact I Thermal Contact I

Two different objects receive the same amount of heat. Which of the following choices is NOT a reason why the objects may have different temperature changes?

1) they have different initial temperatures

2) they have different masses

3) they have different specific heats

ConcepTest 16.8bConcepTest 16.8b Thermal Contact II Thermal Contact II

Two different objects receive the same amount of heat. Which of the following choices is NOT a reason why the objects may have different temperature changes?

1) they have different initial temperatures

2) they have different masses

3) they have different specific heats

Since QQ = = m cm c TT and the objects received the same amount of

heat, the only other factors are the masses and the specific heats. While the initial temperature is certainly relevant for finding the final temperature, it does not have any effect on the temperature change T.

ConcepTest 16.8bConcepTest 16.8b Thermal Contact II Thermal Contact II

ConcepTest 16.9ConcepTest 16.9 Two Liquids Two Liquids

1) the cooler one

2) the hotter one

3) both the same

Two equal-mass liquids, initially at the

same temperature, are heated for the same

time over the same stove. You measure

the temperatures and find that one liquid

has a higher temperature than the other.

Which liquid has a higher specific heat?

Both liquids had the same increase in internal energy,

because the same heat was added. But the cooler liquidcooler liquid

had a lower temperaturelower temperature change.

Since QQ = = mcmcTT, if QQ and mm are both the same and TT is

smaller, then cc (specific heat) must be bigger.

ConcepTest 16.9ConcepTest 16.9 Two Liquids Two Liquids

1) the cooler one

2) the hotter one

3) both the same

Two equal-mass liquids, initially at the

same temperature, are heated for the same

time over the same stove. You measure

the temperatures and find that one liquid

has a higher temperature than the other.

Which liquid has a higher specific heat?

The specific heat of concrete is

greater than that of soil. A baseball

field (with real soil) and the

surrounding parking lot are warmed

up during a sunny day. Which would

you expect to cool off faster in the

evening when the sun goes down?

1) the concrete parking lot

2) the baseball field

3) both cool off equally fast

ConcepTest 16.10aConcepTest 16.10a Night on the Field Night on the Field

The specific heat of concrete is

greater than that of soil. A baseball

field (with real soil) and the

surrounding parking lot are warmed

up during a sunny day. Which would

you expect to cool off faster in the

evening when the sun goes down?

1) the concrete parking lot

2) the baseball field

3) both cool off equally fast

The baseball field, with the lower specific heat, will change

temperature more readily, so it will cool off faster. The high specific

heat of concrete allows it to “retain heat” better and so it will not cool

off so quickly – it has a higher “thermal inertia.”

ConcepTest 16.10aConcepTest 16.10a Night on the Field Night on the Field

ConcepTest 16.10bConcepTest 16.10b Night on the Beach Night on the Beach

Water has a higher specific

heat than sand. Therefore,

on the beach at night,

breezes would blow:

(1) from the ocean to the beach

(2) from the beach to the ocean

(3) either way, makes no difference

ConcepTest 16.10bConcepTest 16.10b Night on the Beach Night on the Beach

DaytimeDaytime sun heats both the beach and the watersun heats both the beach and the water

» beach heats up fasterbeach heats up faster

» warmer air above beach riseswarmer air above beach rises

» cooler air from ocean moves in underneathcooler air from ocean moves in underneath

» breeze blows ocean breeze blows ocean land land

ccsandsand < < ccwaterwater

NighttimeNighttime sun has gone to sleepsun has gone to sleep

» beach cools down fasterbeach cools down faster

» warmer air is now above the oceanwarmer air is now above the ocean

» cooler air from beach moves out to the oceancooler air from beach moves out to the ocean

» breeze blows land breeze blows land ocean ocean

Water has a higher specific

heat than sand. Therefore,

on the beach at night,

breezes would blow:

(1) from the ocean to the beach

(2) from the beach to the ocean

(3) either way, makes no difference

ConcepTest 16.11ConcepTest 16.11 Calorimetry Calorimetry

1 kg of water at 100 oC is poured into a

bucket that contains 4 kg of water at 0

oC. Find the equilibrium temperature

(neglect the influence of the bucket).

(1) 0 oC

(2) 20 oC

(3) 50 oC

(4) 80 oC

(5) 100 oC

Since the cold water mass is greatercold water mass is greater, it will

have a smaller temperature changesmaller temperature change!

The masses of cold/hot have a ratio of 4:1,

so the temperature change must have a

ratio of 1:4 (cold/hot).

ConcepTest 16.11ConcepTest 16.11 Calorimetry Calorimetry

1 kg of water at 100 oC is poured into a

bucket that contains 4 kg of water at 0

oC. Find the equilibrium temperature

(neglect the influence of the bucket).

(1) 0 oC

(2) 20 oC

(3) 50 oC

(4) 80 oC

(5) 100 oC

QQ11 = = QQ22

mm11ccTT11 = = mm22ccTT22

TT11 / / TT22 = = mm22 / / mm11

Which has more molecules – a

mole of nitrogen (N2) gas or a

mole of oxygen (O2) gas?

1) oxygen

2) nitrogen

3) both the same

ConcepTest 17.1aConcepTest 17.1a Nitrogen and Oxygen INitrogen and Oxygen I

Which has more molecules – a

mole of nitrogen (N2) gas or a

mole of oxygen (O2) gas?

1) oxygen

2) nitrogen

3) both the same

A mole is defined as a quantity of gas molecules equal to

Avogadro’s number (6.02 1023). This value is independent of the

type of gas.

ConcepTest 17.1aConcepTest 17.1a Nitrogen and Oxygen INitrogen and Oxygen I

Which weighs more – a mole

of nitrogen (N2) gas or a mole

of oxygen (O2) gas?

1) oxygen

2) nitrogen

3) both the same

ConcepTest 17.1bConcepTest 17.1b Nitrogen and Oxygen IINitrogen and Oxygen II

Which weighs more – a mole

of nitrogen (N2) gas or a mole

of oxygen (O2) gas?

1) oxygen

2) nitrogen

3) both the same

The oxygen molecules have a molecular mass of 32, while the

nitrogen molecules have a molecular mass of 28.

ConcepTest 17.1bConcepTest 17.1b Nitrogen and Oxygen IINitrogen and Oxygen II

Follow-up:Follow-up: Which one will take up more space? Which one will take up more space?

ConcepTest 17.2aConcepTest 17.2a Ideal Gas Law IIdeal Gas Law I

1) cylinder A

2) cylinder B

3) both the same

4) it depends on temp. T

Two identical cylinders at the same

temperature contain the same gas. If

A contains three times as much gas

as B, which cylinder has the higher

pressure?

Ideal gas law: PVPV = = nRTnRT

Solve for pressure: PP = = nRT / VnRT / V

For constant V and T, the one with more

gas (the larger value of the larger value of nn) has the

higher pressure P.

ConcepTest 17.2aConcepTest 17.2a Ideal Gas Law IIdeal Gas Law I

1) cylinder A

2) cylinder B

3) both the same

4) it depends on temp. T

Two identical cylinders at the same

temperature contain the same gas. If

A contains three times as much gas

as B, which cylinder has the higher

pressure?

ConcepTest 17.2bConcepTest 17.2b Ideal Gas Law IIIdeal Gas Law II

1) cylinder A

2) cylinder B

3) both the same

4) it depends on the

pressure P

Two identical cylinders at the same

pressure contain the same gas. If A

contains three times as much gas as

B, which cylinder has the higher

temperature?

Ideal gas law: PVPV = = nRTnRT

Solve for temperature: TT = = PV / nRPV / nR

For constant V and P, the one with less gas

(the smaller value of the smaller value of nn) has the higher

temperature T.

ConcepTest 17.2bConcepTest 17.2b Ideal Gas Law IIIdeal Gas Law II

1) cylinder A

2) cylinder B

3) both the same

4) it depends on the

pressure P

Two identical cylinders at the same

pressure contain the same gas. If A

contains three times as much gas as

B, which cylinder has the higher

temperature?

ConcepTest 17.2cConcepTest 17.2c Ideal Gas Law IIIIdeal Gas Law III

Two identical cylinders at the same

temperature contain the same gas.

If B has twice the volume and half

the number of moles as A, how does

the pressure in B compare with the

pressure in A?

1) PB = 1/2 PA

2) PB = 2 PA

3) PB = 1/4 PA

4) PB = 4 PA

5) PB = PA

Ideal gas law: PVPV = = nRTnRT

Since BB has a factor of twice the volume, it has a factor of

two less the pressure. But BB also has half the amount of

gas, so that is another factor of two reduction in pressure.

Thus, BB must have only 1/4 the pressure of AA.

ConcepTest 17.2cConcepTest 17.2c Ideal Gas Law IIIIdeal Gas Law III

Two identical cylinders at the same

temperature contain the same gas.

If B has twice the volume and half

the number of moles as A, how does

the pressure in B compare with the

pressure in A?

1) PB = 1/2 PA

2) PB = 2 PA

3) PB = 1/4 PA

4) PB = 4 PA

5) PB = PA

ConcepTest 17.3ConcepTest 17.3 Soda Bottle Soda Bottle

1) it expands and may burst

2) it does not change

3) it contracts and the sides collapse

inward

4) it is too dark in the fridge to tell

A plastic soda bottle is empty

and sits out in the sun,

heating the air inside. Now

you put the cap on tightly and

put the bottle in the fridge.

What happens to the bottle as

it cools?

The air inside the bottle is warmair inside the bottle is warm, due to heating by the

sun. When the bottle is in the fridge, the air coolsthe air cools. As

the temperature drops, the pressure in the bottle also pressure in the bottle also

dropsdrops. Eventually, the pressure inside is sufficiently

lower than the pressure outside (atmosphere) to begin to

collapse the bottle.

ConcepTest 17.3ConcepTest 17.3 Soda Bottle Soda Bottle

1) it expands and may burst

2) it does not change

3) it contracts and the sides collapse

inward

4) it is too dark in the fridge to tell

A plastic soda bottle is empty

and sits out in the sun,

heating the air inside. Now

you put the cap on tightly and

put the bottle in the fridge.

What happens to the bottle as

it cools?

ConcepTest 17.4ConcepTest 17.4 Balloon in FreezerBalloon in Freezer

1) it increases

2) it does not change

3) it decreases

What happens to the volume

of a balloon if you put it in the

freezer?

According to the Ideal Gas Law, when the temperature is when the temperature is

reduced at constant pressurereduced at constant pressure, the volume is reducedvolume is reduced as well.

The volume of the balloon therefore decreases.

ConcepTest 17.4ConcepTest 17.4 Balloon in FreezerBalloon in Freezer

nRTPV

1) it increases

2) it does not change

3) it decreases

What happens to the volume

of a balloon if you put it in the

freezer?

Follow-up:Follow-up: What happens to the volume What happens to the volume when the balloon rises in the air?when the balloon rises in the air?

If you add some heat to a substance,

is it possible for the temperature of

the substance to remain unchanged?

1) yes

2) no

ConcepTest 17.5ConcepTest 17.5 Adding HeatAdding Heat

If you add some heat to a substance,

is it possible for the temperature of

the substance to remain unchanged?

1) yes

2) no

Yes, it is indeed possible for the temperature to stay the same. This is precisely what occurs during a phase change – the added heat goes into changing the state of the substance (from solid to liquid or from liquid to gas) and does not go into changing the temperature! Once the phase change has been accomplished, then the temperature of the substance will rise with more added heat.

ConcepTest 17.5ConcepTest 17.5 Adding HeatAdding Heat

Follow-up:Follow-up: Does that depend on the substance?

Will potatoes cook faster if the

water is boiling faster? 1) yes

2) no

ConcepTest 17.6ConcepTest 17.6 Hot PotatoHot Potato

Will potatoes cook faster if the

water is boiling faster? 1) yes

2) no

The water boils at 100 °C and remains at that temperature until all of the water has been changed into steam. Only then will the steam increase in temperature. Since the water stays at the same temperature, regardless of how fast it is boiling, the potatoes will not cook any faster.

ConcepTest 17.6ConcepTest 17.6 Hot PotatoHot Potato

Follow-up:Follow-up: How can you cook the potatoes faster?

ConcepTest 17.7ConcepTest 17.7 Water and Ice Water and Ice

You put 1 kg of ice at 0oC

together with 1 kg of water at

50oC. What is the final

temperature? LF = 80 cal/gcwater = 1 cal/g oC

1) 0oC

2) between 0oC and 50oC

3) 50oC

4) greater than 50oC

How much heat is needed to melt the ice?

QQ = = m Lm Lff = (1000= (1000gg) ) (80 cal/ (80 cal/gg) = 80,000 cal) = 80,000 cal

How much heat can the water deliver by cooling from 50oC to 0oC?

QQ = = ccwaterwater mmTT = (1 cal/ = (1 cal/gg ooC) C) (1000 (1000gg) ) (50 (50ooC) = 50,000 calC) = 50,000 cal

Thus, there is not enough heat available to melt all the ice!!

ConcepTest 17.7ConcepTest 17.7 Water and Ice Water and Ice

You put 1 kg of ice at 0oC

together with 1 kg of water at

50oC. What is the final

temperature? LF = 80 cal/gcwater = 1 cal/g oC

1) 0oC

2) between 0oC and 50oC

3) 50oC

4) greater than 50oC

Follow-up:Follow-up: How much more water at 50oC would you need?

ConcepTest 17.8ConcepTest 17.8 Ice and Steam Ice and Steam

You put 1 kg of ice at 0oC

together with 1 kg of steam at

100oC. What is the final

temperature? LF = 80 cal/g, Lv = 540 cal/gcwater = 1 cal/g oC

1) between 0oC and 50oC

2) 50oC

3) between 50oC and 100oC

4) 100oC

5) greater than 100oC

How much heat is needed to melt the ice?

Q Q = = m Lm Lff = (1000= (1000gg) ) (80 cal/ (80 cal/gg) = 80,000 cal) = 80,000 cal

How much heat is needed to raise the water temperature to 100oC?

QQ = = ccwaterwater mmTT = (1 cal/ = (1 cal/gg ooC)C)(1000(1000gg))(100(100ooC) = 100,000 calC) = 100,000 cal

But if all of the steam turns into water, that would release 540,000 cal540,000 cal.

Thus, some steam is left over, and the whole mixture stays at 100oC.

ConcepTest 17.8ConcepTest 17.8 Ice and Steam Ice and Steam

You put 1 kg of ice at 0oC

together with 1 kg of steam at

100oC. What is the final

temperature? LF = 80 cal/g, Lv = 540 cal/gcwater = 1 cal/g oC

1) between 0oC and 50oC

2) 50oC

3) between 50oC and 100oC

4) 100oC

5) greater than 100oC

Follow-up:Follow-up: How much more ice would you need?

ConcepTest 17.9ConcepTest 17.9 You’re in Hot Water!You’re in Hot Water!

Which will cause more severe burns

to your skin: 100 °C water or 100 °C

steam?

1) water

2) steam

3) both the same

4) it depends...

While the water is indeed hot, it releases only 1 cal/1 cal/gg of heat as it

cools. The steam, however, first has to undergo a phase phase

changechange into water and that process releases 540 cal/g540 cal/g, which is

a very large amount of heat. That immense release of heat is

what makes steam burns so dangerous.

ConcepTest 17.9ConcepTest 17.9 You’re in Hot Water!You’re in Hot Water!

Which will cause more severe burns

to your skin: 100 °C water or 100 °C

steam?

1) water

2) steam

3) both the same

4) it depends...

ConcepTest 17.10ConcepTest 17.10 Spring BreakSpring Break

You step out of a swimming

pool on a hot day, where the

air temperature is 90° F.

Where will you feel cooler, in

Phoenix (dry) or in

Philadelphia (humid)?

1) equally cool in both places

2) Philadelphia

3) Phoenix

In Phoenix, where the air is dry, more of the water will

evaporate from your skin. This is a phase change,

where the water must absorb the heat of vaporization,

which it takes from your skin. That is why you feel

cool as the water evaporates.

ConcepTest 17.10ConcepTest 17.10 Spring BreakSpring Break

You step out of a swimming

pool on a hot day, where the

air temperature is 90° F.

Where will you feel cooler, in

Phoenix (dry) or in

Philadelphia (humid)?

1) equally cool in both places

2) Philadelphia

3) Phoenix

ConcepTest 18.1ConcepTest 18.1 Free Expansion Free Expansion A free expansion occurs when a valve is opened allowing a gas to expand into a bigger container. In such an expansion the temperature of the gas will:

1) increase

2) decrease

3) stay the same

ConcepTest 18.1ConcepTest 18.1 Free Expansion Free Expansion A free expansion occurs when a valve is opened allowing a gas to expand into a bigger container. In such an expansion the temperature of the gas will:

1) increase

2) decrease

3) stay the same

In such a process:W = 0 there is no object to move,Q = 0 there is no heat exchange, thereforeU = 0 by the First Law of Thermodynamics.Thus, there is no change in the temperature.

Free expansion is neither adiabatic nor isothermal expansion, even though T and Q are zero.

Free expansion is an irreversible process --- the gas molecules have virtually no chance of returning to the original state.

ConcepTest 18.2ConcepTest 18.2 Work Work

In the closed thermodynamic

cycle shown in the P-V diagram,

the work done by the gas is:

1) positive

2) zero

3) negative

V

P

ConcepTest 18.2ConcepTest 18.2 Work Work

In the closed thermodynamic

cycle shown in the P-V diagram,

the work done by the gas is:

1) positive

2) zero

3) negative

The gas expands at a higher pressure

and compresses at a lower pressure.

In general, clockwise = positive work;

counter-clockwise = negative work.

V

P

ConcepTest 18.3ConcepTest 18.3 Heat Engine Heat Engine

The heat engine below is: 1) a reversible (Carnot) heat engine

2) an irreversible heat engine

3) a hoax

4) none of the above

ConcepTest 18.3ConcepTest 18.3 Heat Engine Heat Engine

The heat engine below is: 1) a reversible (Carnot) heat engine

2) an irreversible heat engine

3) a hoax

4) none of the above

Carnot e = 1-TC/TH=1-270/600=0.55.

But by definition e = 1-QL/QH

=1 - 4000/8000=0.5, smaller

than Carnot e, thus irreversible.

Follow-up:Follow-up: What would you need to change to make it a Carnot engine? What would you need to change to make it a Carnot engine?