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ConcepTest PowerPoints

Chapter 15

Physics: Principles with Applications, 6th edition

Giancoli

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 13.8aConcepTest 13.8a 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 13.8aConcepTest 13.8a 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 13.8bConcepTest 13.8b 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 13.8bConcepTest 13.8b 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 13.9aConcepTest 13.9a 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 13.9aConcepTest 13.9a 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 13.9bConcepTest 13.9b 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 13.9bConcepTest 13.9b 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 13.9cConcepTest 13.9c 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 two more volume, it has a factor of two

less 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 13.9cConcepTest 13.9c 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 13.10ConcepTest 13.10 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 13.10ConcepTest 13.10 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 13.11ConcepTest 13.11 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 13.11ConcepTest 13.11 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?

ConcepTest 15.1ConcepTest 15.1 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 15.1ConcepTest 15.1 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 15.2ConcepTest 15.2 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 15.2ConcepTest 15.2 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 = negative work;

counterclockwise = positive work.

V

P

ConcepTest 15.3ConcepTest 15.3 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 15.3ConcepTest 15.3 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.

Draw a P-V DiagramDraw a P-V Diagram

Isothermal process Adiabatic process Isochoric process Isobaric process

Draw a T-V DiagramDraw a T-V Diagram

Isothermal process Adiabatic process Isochoric process Isobaric process