Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Fall 2013 > Physics II > Flashcards

Physics II Flashcards

1
Q

What is an isobaric process?

A

An isobaric process is a prcoess that takes place at constant pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
1
Q

The efficiency of a Carnot engine operating between two heat resevoirs and using an ideal gas as the working fluid is given by:

ε = (TH - TC)/TH

What is the efficiency if the working fluid is some other non-ideal gas?

A

The efficiency is the same, regardless of the working fluid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the difference between a reversible process and an an irreversible process?

A

A reversible process takes place slowly, so that the system is not taken out of equilibrium.

An irriversible process takes place quickly, so that the system us taken out of equilibrium.

(A truly reversible process would take place in an infinite ammount of time)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

For an ideal gas, find an expression for the following quantity:

( ∂P/ ∂T)V

A

nR/V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

True or False?

The entropy of the universe always increases when a process occurs; it never decreases.

A

True. Entropy of the universe increases when a spontaneous process occurs, but spontaneous processes are the only processes that occur. Hence the entropy of the universe always increases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is special about the change in state function called enthalpy?

ΔH

A

For a process teking place at constant pressure, the change in enthalpy gives the heat added to the system.

ΔH = Q

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Who investigated the properties of gases and found that at constant pressure, the volume is proportional to the temperature?

A

Jacques Charles, 1787

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Who investigated the properties of gases and found that at constant temperature the pressure is inversely proportional to the volume?

A

Robert Boyle, 1662

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the relation between P and V for a reversible adiabatic expansion of an ideal gas?

A

P = const./Vγ

Where the exopnent is:

γ = CP/CV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the efficiency of a Carnot cycle running between a hot resevoir at TH and a cold resevoir at TC?

A

ε = (TH - TC)/TH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the heat capacity at constant volume for an ideal gas consisting of diatmic molecules?

A

Cv = 5/2 (nR)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The first law is said to be a postulate consisting of two parts. What are these two parts?

A

The first postulate of the first law is our postulate that the energy of the universe never changes.

The second part of the first law is the postulate that energy U is a state function.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What four ssteps make up the thermoynamic cycle of the Stirling engine?

A

1) Isothermal (Constant Temperature) expansion at TH,
2) Isochoric (Constant Volume) cooling to TC,
3) Isothermal compression at TC,
4) Isothermal heaing back to TH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What postulate concerning energy forms the basis of the First Law of Thermodynamics?

A

The energy of the universe remains constant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What four steps make up the thermodynamic cycle of the Carnot engine?

A

1) Isothermal reversible expansion at TH
2) Adiabatic reversible expansion to lower the temperature to TC
3) Isothermal reversible compression at TC
4) Adiabatic reversible compression to raise the temperature back to TH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Who showed that the energy of an dieal gas depends only on its temperature? THey also measured the dependance of U with V for real gases.

A

James Joule and William Thomson (later to be Lord Kelvin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The surroundings are always assumed to take on heat (or give off heat) in a reversible fashion. Why?

A

The srroundings is the
“rest of the universe”, an infinite resevoir. Thus when any finite ammount of heat from the system is spread throughout the surroundings, the perturbation to the state of the surroundings is negligible. Hence the surroundings remain in equilibrium.

16
Q

True or False?

The state of a system is entirely determined by the specification of just two state variables.

A

True.

For example, if you specify V and T for an ideal gas, then you can figure out P from the equation of state.

You can also figure out U since U is

CV * T

(We are assuming that the number of moles of gas is known)

18
Q

What is important about the change in state function called internal energy?

ΔU

A

For a process taking place at constant colume, the change in the energy is equal to the heat added to the system
.

ΔU = Q

18
Q

Reversible work is performed when the difference between the pressure of the system and the presure of the surroundings is infitessimal.

What is the analogous requirement on temperature so that heat is transferred reversibly?

A

There should be an infitessimal difference between the temperature of the system and the temperature of the surrounding in order to keep the system in equilibrium.

(The surroundings always stays in equilibrium because of its vast size)

19
Q

What is the relation between the heat capacity at constant pressure and the heat capacity at constant volume for an ideal gas?

A

CP = CV + nR

20
Q

What convention do we follow?

a) Q the heat added to the system from the surroundings

or

b) Q the heat passed to the surroundings from the system

A

a) Q is the heat added to the system frim the surroundings.

Thus Q is positive if the heat is transferred to the system from the surroundings, and Q is negative if the heat is transferred from the system to the surroundings.

21
Q

What convention do we follow?

a) W the work done on the system by the surroundings

or

b) W the work done on the surroundings by the system

A

b)

Our convention is that W is the work done on the surroundings by the system.

If the system does work on the surroundings, W is positive. If the surroundings do work on the system, W is negative

22
Q

What is the connection between an irreversible process and a spontaneous process

A

All spontaneous prcess, i.e. processes that occur in a finite ammount of time, require an imalance of forces. They are therefore irreversible processes.

24
Q

True or False?

It can be proved that the heat capacity at constant pressure is greater thean the heat capacity at constant volume regardless of the substance.

A

True

25
Q

In thermodynamics we talk about the system and the surroundings.

What is the system?

What is the surroundings?

A

The system is that part of the universe on which we are focusing our attention. The surroundings is the rest of the universe.

26
Q

The energy of a certain real (non-ideal) gas is given by

U = 3/2 (nRT) - a(n2/V2)

What is the heat capacity at constant volume?

A

Answer:

Cv = (∂U/∂T)V = 3/2(nR)

28
Q

True or False?

The entropy of S is a state function.

It is sometimes related to heat, and sometimes not realated to heat.

It is related to heat when heat is transferred reversibly.

A

True.

29
Q

The energy of a certain real (non-ideal) gas is given by

U = 3/2 (nRT) - a (n2/V2)

The equation of state for the gas is

Pv = nRT - a (n2/V2)

Find the enthalpy H(T,V) as a function of T and V

A

Answer:

Remember the definition H = U + PV

H = U + PV

= 5/2 (nRT) - 2a (n2/V)

30
Q

The energy of a certain real (non-ideal) gas is given by

U = (3/2)nRT - a (n2/V)

Calculate the coefficients of expansion of U(T,V) in the variables T anad V.

A

Answer:

∂U = (∂U/∂T)V dT + (∂U/∂V)T dV

(∂U/∂T)V = 3/2 (nR)

(∂U/∂V)T = a(n2/V2)

31
Q

What mathematical relation is reagarded as a formal statement of the first law of thermodynamics?

A

ΔU = Q - W

32
Q

Who is credited with figuring out the second law of thermodynamics?

A

Rudolph Clausius, 1850

33
Q

Who devised a hypothetical heat engine that could be run reversibly between two heat, one resevoirs kept at a hot temperature and the other at a cold temperature?

A

Sadi Carnot, 1820

34
Q

What is an adiabatic process?

A

This is a process that takes place in an insulated contianer so that no heat is exchanged with the surroundings.

35
Q

Who patented a heat engine in 1816, for the purpose of powering underwater torpedos without leabing a trail of bubbles?

A

Robert Stirling, 1816

36
Q

True or False?

The energy of an ideal gas is given by the following expression:

U = CV * T

A

True.

The energy og an ideal gas is a function of temerature only. Since the derivative of U with respect to T is equal to

CV

it follows that

CV

is the proportionality constant between U and T

37
Q

A system consists of an ice cube. It is initially at a temperature of 270 K and a pressure of 1 atm. It melts, becoming water at 294 K and a pressure of 1 atm.

True or False?

The change in the entropy of the ststem depends on whether the melting takes place slowly or quickly.

A

False.

Entropy is a state function so the change in S only dpeends on the final and initial states. It does not depend on the path taken to go from one state to the other.

38
Q

What is an isochoric process?

A

An isochoric process is a process that takes place at constant volume.

39
Q

True or False?

If a piston expands irreversibly, it is impossible to calculate the work because it is impossible to dtermine the integral

∫PdV

because we have no way out of assigning P to a system out of equilibrium.

A

False.

Even if we can’t define the equilibrium pressure of the gas, we can still measrue the extermal pressure on the piston as a function of volume, in principle.

The work is the integral

∫Pext dV

40
Q

True or False?

The entropy of a system always increases when a process occurs spontaneously.

A

False.

It is the sum of the entropy of the system plus the entropy of the surroundings that always increases for a spontaneous process, i.e. the entropy of the universe always increases.

41
Q

What is an isothermal process?

A

This is a process that takes place at constant temperature. What this means is that the final temperature of the system is equal to the initial temperature of the system.

42
Q

True or False?

All reversible heat engines operating between two heat resevoirs have the same efficiency?

A

True, they all have the same efficiency, regardless of the working fluid. The efficiency is the Carnot efficiency.

ε = (TH - TC)/TH

(The only reversible engine we can imagine is the Carnot engine)

Fall 2013 (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions