Thermodynamics

Question 1

What is thermal equilibrium?

Answer 1

Two systems are in thermal equilibrium with each other if they have the same temperature

Question 2

Zeroeth Law of thermodynamics

Answer 2

If two systems A and B are separately in thermal equilibrium with a third system C, then A and B are also in thermal equilibrium with each other.

Question 3

Internal Energy

Answer 3

Internal energy of a system is the sum of molecular kinetic and potential energies in the frame of reference to which the center of mass of the system is at rest

Question 4

Intermolecular potential energy corresponds to

Answer 4

Volume

Question 5

Intermolecular kinetic energy corresponds to

Answer 5

Temperature

Question 6

Heat

Answer 6

Mode of energy transfer due to temperature difference between system and surroundings

Question 7

Work

Answer 7

Mode of energy transfer brought about by means that do not involve temperature difference

Question 8

Sign Convention

(Heat, Work, Internal Energy)

Answer 8

Heat Absorbed = +
Work Done By system = +
Increase in internal energy = +

Question 9

Work Done

Derivation

Answer 9

dW = Fdx = PA dx = Pdv
W = integral (PdV)

Question 10

Non-cyclic process

Answer 10

System does not return to its initial state

Question 11

Work Done (Cyclic Process)

Explain what is + and -

Answer 11

Work taken in clockwise = +
Work taken in anti-clockwise = -

Question 12

Cyclic Process

Answer 12

Any process in which the system returns to its initial state after undergoing a series of changes

Question 13

First Law of Thermodynamics

Answer 13

If some heat is supplied to a system which is capable of doing work, then the quantity of heat absorbed by the system will be equal to the sum of increase in its internal energy and the external work done by system

Question 14

First Law of Therm (Formula)

Answer 14

delta Q = delta U + delta W {or P delta V}

Question 15

Specific heat during adiabatic change

Answer 15

Zero

delta Q = 0

Question 16

specific heat during isothermal

Answer 16

Infinite

delta T = 0; 1/0 = infinity

Question 17

Change in temp (on specific heat)

Answer 17

delta T = + specific heat = +
delta T = - specific heat = -

Question 18

Why is Cp > Cv

specific heat at constant p > constant v

Answer 18

• Heat at constant volume uses all energy to increase temp
• Heat at constant p causes expansion = work against external pressure. Hence, additional amount of heat equivalent to work done is used

Question 19

Cp - Cv formula

Answer 19

Cp - Cv = R / J

R is the gas constant

Question 20

Isothermal Process

Answer 20

Thermodynamic process at constant temp

Question 21

Isobaric process

Answer 21

Thermodynamic process at constant pressure

Question 22

Isochoric process

Answer 22

Thermodynamic process at constant volume

Question 23

Adiabatic

Answer 23

Thermodynamic process having no heat exchange

Question 24

Conditions for isothermal process

Answer 24

1. Walls must be perfectly conducting to allow free exchange of heat
2. Process of compression or expansion should be very slow

Question 25

Isothermal Process (formula)

For P1, V1

Answer 25

P1V1 = P2V2

Question 26

Explain effect of gas expanding isothermally

Answer 26

• Internal energy dependent only on temp –> delta U = 0
• delta Q = P delta V
• If V increases = Q increases (+)
• An amount of heat = work done by gas has to be supplied

Question 27

Derive expression for work done during isothermal expansion

Answer 27

W = 2.303 nRT log V2 / V1

actually derive it

Question 28

Conditions for adiabatic

Answer 28

1. Walls of container must be perfectly insulated
2. compession or expansion should be sudden so heat is not exchanged

Question 29

Adiabatic relation between P and V

Answer 29

PV^(Cp / Cv) = K

derive it

Question 30

Adiabatic relation between P and T

Answer 30

[P^(1-Cp/Cv)] * T^(Cp/Cv) = constant

derive

Question 31

Adiabatic relation between T and V

Answer 31

TV^(Cp/Cv - 1) = constant

derive itx

Question 32

Work done in adiabatic

Answer 32

W = [1/(gamma - 1)] (P1V1 - P2V2)

derive

Question 33

Work done in adiabatic (in moles)

Answer 33

W = nR/(gamma - 1) * (T1 - T2)

derive

Question 34

First Law applied to isochoric

Answer 34

Q = delta U + delta W = delta U ( volume is constant)
Q = nCv delta T

Question 35

First Law applied to cyclic

Answer 35

Q = delta U + W = 0 + W = W
(No change in internal energy)

Total heat absorbed = work done by system

Question 36

First Law of therm in boiling

Answer 36

Uf - Ui = mL - P(Vf - Vi)

Question 37

First Law applied to isobaric

Answer 37

W = nR(T2 - T1)
Absorbed heat goes partly to increase internal energy

Question 38

Second Law of Thermodynamics

Answer 38

A simple statement of the law is that heat always flows spontaneously from hotter to colder regions of matter. “Not all heat can be converted into work in a cyclic process.”

Question 39

Reversible Processes

Answer 39

Any process which can be made to proceeed in the reverse direction by variation in its conditions such that any change occuring in any part of reversible process

Question 40

Conditions for reversible process

Answer 40

An infinitesimally slow compression and expansion of an ideal gas at constant temperature

Question 41

Irreversible process

Answer 41

Any process which cannot be retaced in the reverse direction exactly

Question 42

1g of water at 100∘C is converted into steam at the same temperature. If the volume of steam is 1671cm3, find the change in the internal energy of the system. Latent of steam = 2256 Jg−1. Given 1 atmospheric pressure = 1.013 × 10^5 Nm−2

Answer 42

2086.829J

Question 43

Why is slope of adiabatic steeper than isothermal?

Answer 43

Adiabatic –> PV^gamma
Isothermal –> PV
Since gamma > 1; pressure inversely prop. (adiabatic > isothermal)

Question 44

Quasi Static Process

Answer 44

State ariables of a thermodynamical system change infinitely slowly
Hypothetical and reersible

Question 45

Cyclic process properties

Answer 45

1. Isothermal
2. Delta U = 0

Question 46

Hi

Answer 46

fij