Thermodynamics

Question 1

During adiabatic expansion of an ideal gas work is done by the system and its internal energy ________.

Answer 1

Decreases

Question 2

Maximum work that could be secured by expanding the gas over a given pressure range is the _______ work.
A.isothermal
B. Adiabatic
C. Isentropic
D. None of these

Answer 2

Isothermal
R: Larger area in PV diagram compared to adiabatic

Question 3

Internal energy change of a system over one complete cycle in a cyclic process is
A.zero
B. Positive
C. Negative
D. Dependent on the path

Answer 3

Zero
R: delta T is zero therefore delta U is zero

Question 4

Van Laar equations deals with the activity coefficients in

Answer 4

Binary solution

Question 5

High ______ is an undesirable property for a good refrigerant

Answer 5

Viscosity
Desirable: high latent heat of vaporization to get more refrigeration effect
Large conductivity to reduce size of condenser and evaporator
Low specific volume

Question 6

Solubility of a substance which dissolves with an increase in volume and liberation of heat will be favoured by the

Answer 6

Low P and Low T

Question 7

A chemical reaction will occur spontaneously at constant pressure and temperature, if the free energy is

Answer 7

Negative

Question 8

For a spontaneous process, free energy

Answer 8

decreases whereas the entropy increases
DeltaG is equal to delta H -T delta S

Question 9

A refrigeration cycle is a reversed heat engine. Which of the following has the maximum value of the co-efficient of performance (COP) for a given refrigeration effect ?
Vapor compression cycle using expansion valve.
Air refrigeration cycle.
Vapor compression cycle using expansion engine.
Carnot refrigeration cycle.

Answer 9

Carnot refrigeration cycle

Question 10

In a working refrigerator, the value of COP is always
0
< 0
< 1
> 1

Answer 10

> 1

Question 11

__________ increases with increase in pressure.
The melting point of wax
The boiling point of a liquid
both (a) and (b)
neither (a) nor (b)

Answer 11

both (a) and (b)
Metal melting point increses with increase in pressure while water melting point decrease in pressure increase

Question 12

For a stable phase at constant pressure and temperature, the fugacity of each component in a binary system __________ as its mole fraction increases

Answer 12

increases
We know for an ideal binary solution by Lewis-Randall rule fugacity of a component is directly proportional to mole fraction of that component. So basically on increasing the mole fraction the fugacity of the component is increasing but this equation is valid only for an ideal solution but, we can extend this behavior for real solution also under some conditions.
Fugacity is a measure of the effective partial pressure of a chemical species under non-ideal conditions

Question 13

Out of the following refrigration cycles, which one has the minimum COP (Co-efficient of performance)?
Air cycle
Carnot cycle
Ordinary vapour compression cycle
Vapour compression with a reversible expansion engine

Answer 13

Air cycle has minimum coefficient of performance.

Question 14

The theoretical minimum work required to separate one mole of a liquid mixture at 1 atm, containing 50 mole % each of n- heptane and n- octane into pure compounds each at 1 atm is
-2 RT ln 0.5
-RT ln 0.5
0.5 RT
2 RT

Answer 14

w = -nRTlnP1/P2.
where n=1
p1 = 1.
p2 = 1+1 = 2.

=> w = -RTln 0.5.

Question 15

Entropy of an ideal gas depends upon its
pressure
temperature
both (a) & (b)
neither (a) nor (b)

Answer 15

Delta S = Cp ln(T2/T1)-R ln(P2/P1).

Question 16

If the vapour pressure at two temperatures of a solid phase in equilibrium with its liquid phase are known, then the latent heat of fusion can be calculated by the

Answer 16

Clayperon-Claussius equation

Question 17

The freezing point of a liquid decreases when the pressure is increased, if the liquid __________ while freezing.

Answer 17

***Solution(By Examveda Team)
FROM the P-V-T diagram we can say that if the freezing point decreases with increase in pressure than liquid should contract during freezing.

Usually as pressure increases both melting point increases. Consequently Water expands when it freezes. Most liquids contract when they freeze so this property of water is unusual. This property is clearly shown in this experiment. This process is used to explain how ice can break rocks apart.

When liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%.

Question 18

During Joule-Thomson expansion of gases

Answer 18

The Joule–Thomson expansion refers to a method of expansion in which a gas or liquid at pressure P1, without a considerable change in kinetic energy, flows into a region of lower pressure P2. The expansion is certainly inherently irreversible. During such an expansion, there would be no change in enthalpy.

Question 19

Degress of freedom at triple point will be

Answer 19

0

Question 20

Accentric factor is always

Answer 20

<1

Question 21

“Law of corresponding states” says that

Answer 21

two different gases behave similarly, if their reduced properties (i.e. P, V and T) are same.

Question 22

Linde gas liquefaction process employs cooling

Answer 22

By throttling
Linde gas liquefication process is a throttling process where gas is kept below its inversion temperature so on decreasing the pressure (throttling) the temperature decreases and cooling occurs.

Question 23

Joule-Thomson experiment is

Answer 23

Isenthalpic and adiabatic gas is pushed through a porous plug
The study of the dependence of the energy and enthalpy of real gases on volume (pressure) was done by Joule in association with Thomson who devised a different procedure. They allowed gas to expand freely through a porous plug, or frit
The cooling produced in the Joule-Thomson expansion has made it a very valuable tool in refrigeration. The effect is applied in the Linde technique in the petrochemical industry, where the cooling effect is used to liquefy gases. It is also used in many cryogenic applications

Question 24

Pick out the wrong statement pertaining to the decomposition of PCl5 represented by, PCl5 PCl3 + Cl2.Degree of dissociation of PCl5 will
decrease on addition of Cl2.
increase on addition of an inert gas at constant pressure.
decrease on increasing the pressure of the system.
none of these

Answer 24

*** none of these
decrease on addition of Cl2. Backward
decrease on increasing the pressure of the system. Increase pressure lower volume by boyles law then the eqbm will shift towards the side with fewer moles to relieve some pressure
increase on addition of an inert gas at constant pressure. Forward rxn

Question 25

Boyle’s law for gases states that

Answer 25

P is inversely proportional to V, when temperature & mass of the gas remain constant.
Ideal boyles law is applicable forisothermal
Charles law isobaric ideal

Question 26

In a reversible chemical reaction (where, Δx = number of moles of products-number of moles of reactants )
addition of inert gas favours the forward reaction, when Δx is positive.
pressure has no effect on equilibrium, when Δn = 0.
addition of inert gas has no effect on the equilibrium constant at constant volume for any value of Δx (+ ve, - ve) or zero).
all ‘a’, ‘b’ & ‘c’.

Answer 26

Aota

Question 27

Pick out the correct statement:
In an isothermal system, irreversible work is more than reversible work.
Under reversible conditions, the adiabatic work is less than isothermal work.
Heat, work, enthalpy and entropy are all ‘state functions’.
Matter and energy can not be exchanged with the surroundings in a closed system.

Answer 27

Under reversible conditions, the adiabatic work is less than isothermal work.
Draw pv diagram

Question 28

In any spontaneous process,
only F decreases
only A decreases
both F and A decreases
both F and A increase

Answer 28

both F and A decreases
Here by F and A means Gibbs free energy and Helmholtz free energy, as we know that in a spontaneous process free energy always decreases while entropy increases. So best option is C.Helmholtz free energy is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature. Helm holtz = U - TS

Question 29

Equilibrium constant decreases as the temperature

Answer 29

Increases for an exothermic reaction

Meanwhile Kp increases as T increases for endothermic reaction

Emelang ituuu like di ko siya makuha if ito ang gagmitin Le chatelier if deltahis positive endothermic plus heat on the reactant side then treat heat as reactant

Question 30

The expression, deltaG equals nRT ln P2/P1 , gives the free energy change
with pressure changes at constant temperature.
under reversible isothermal volume change.
during heating of an ideal gas.
during cooling of an ideal gas.

Answer 30

with pressure changes at constant temperature. know, the property relation:
dG=vdp−sdT

Which is valid for both reversible and irreversible process since it is a property relation. when the system undergoes isothermal change dT=0

So, dG=vd⇒dG=nRTPdP(for, ideal gas)

On, integration
⇒ΔG=nRT.lnP2P1

So, for a system containing ideal gas and undergoing isothermal change of volume or pressure this expression is valid.

Question 31

All gases during throttling process at atmospheric temperature and pressure show a cooling effect except

Answer 31

At room temperature, all gases except hydrogen, helium, and neon cool upon expansion by the Joule–Thomson process when being throttled through an orifice; these three gases experience the same effect but only at lower temperatures.

Question 32

Compressibility factor for almost all the gases are approximately same at the same

Answer 32

reduced pressure and reduced temperature
Since compressibility factor (Z
) is an function of reduced temperature and reduced pressure i..e.., Z=fn(Pr,Tr).
At same Pr
and Tr
the compressibility factor remains constant.

Question 33

Pick out the wrong statement.
Activity co-efficient is dimensionless.
In case of an ideal gas, the fagacity is equal to its pressure.
In a mixture of ideal gases, the fugacity of a component is equal to the partial pressure of the component.
The fugacity co-efficient is zero for an ideal gas.

Answer 33

The fugacity co-efficient is zero for an ideal gas.
F/P
activity coefficient is a dimensionles
measure of how much a solution differs from an ideal solution unity if ideal

Conversely, when activity coefficient is greater than 1.0, it implies that molecules have strong repelling force and exhibits positive deviation from Raoult’s law. In this case, lesser energy is needed to separate the constituent molecules.In thermodynamics, an activity coefficient is a factor used to account for deviation of a mixture of chemical substances from ideal behaviour.

Question 34

The chemical potential of a component (μi) of a phase is the amount by which its capacity for doing all work, barring work of expansion is increased per unit amount of sustance added for an infinitesimal addition at constant temperature and pressure. It is given by

Answer 34

aota screenshot 2 2 2023

Question 35

In jet refrigerators, the refrigerating fluid is practically always

Answer 35

Water

Question 36

Water on heating from 1 to 4°C

Answer 36

Contracts
Though liquids expand on heating, water does not expand between 0°C to 4°C instead it contracts as water has maximum density at 4°C. It expands above 4°C.

Question 37

When pressure is applied on the system, ice <->water, then

Answer 37

More water will be formed.
Water has lesser volume as compared to Ice (Due to the anamolous expansion of water.) Hence an increase in pressure would favor the forward reaction which leads to lesser volume.

Question 38

Partial molar free energy of an element A in solution is same as its

Answer 38

Chemical potential

Question 39

Free energy change at equilibrium is

Answer 39

Zero

Question 40

Heat pump
accomplishes only space heating in winter.
accomplishes only space cooling in summer.
accomplishes both (a) and (b).
works on Carnot cycle.

Answer 40

Both a and b

Question 41

The temperature at which both liquid and gas phases are identical, is called the __________ point.

Answer 41

Critical point

Question 42

What is the value of ln y (where y = activity co-efficient) for ideal gases ?

Answer 42

Zero
Activity coefficient of ideal gas is 1

Question 43

A closed system is cooled reversibly from 100°C to 50°C. If no work is done on the system
its internal energy (U) decreases and its entropy (S) increases.
U and S both decreases
U decreases but S is constant.
U is constant but S decreases.

Answer 43

U and S both decreases

Question 44

Which is not a refrigerant ?
SO2
NH3
CCl2F2
C2H4Cl2

Answer 44

C2H4Cl2 dichloroethane
Ccl2f2 freon12Dichlorodifluoromethane
Low-molecular weight hydrocarbons, hydrofluorocarbons (HFCs), ammonia and nitrogen are commonly used as the refrigerant; since 1987, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are being phased out [7,8].

Question 45

The partial pressure of each constituent present in an alloy is __________ the total vapor pressure exerted by the alloy.

Answer 45

Less than

Question 46

Heat is added at constant pressure in an ideal __________ cycle.

Answer 46

Brayton and Rankine

Question 47

Entropy change of mixing two liquid substances depends upon the
molar concentration
quantity (i.e. number of moles)
both (a) and (b)
neither (a) nor (b)

Answer 47

both (a) and (b)

Question 48

The four properties of a system viz. P, V, T, S are related by __________ equation.

Answer 48

Maxwells eqn

Question 49

If the pressure on 100 c.c. of air is halved, then its volume (at the same temperature) would be __________ c.c.

Answer 49

200

Question 50

Pick out the wrong statement.
Cp of monoatomic gases such as metallic vapor is about 5 kcal/kg.atom.
The heat capacity of solid inorganic substance is exactly equal to the heat capacity of the substance in the molten state.
There is an increase in entropy, when a spontaneous change occurs in an isolated system.
At absolute zero temperature, the heat capacity for many pure crystalline substances is zero.

Answer 50

The heat capacity of solid inorganic substance is exactly equal to the heat capacity of the substance in the molten state.

Question 51

The principle applied in liquefaction of gases is
adiabatic expansion.
Joule-Thomson effect.
both (a) and (b).
neither (a) nor (b).

Answer 51

both (a) and (b).

Question 52

Co-efficient of performance for a reversed Carnot cycle working between temperatures T1 and T2 (T1 > T2) is

Answer 52

T2/(T1-T2)
The COP of a Carnot refrigeration cycle is a function only of the upper and lower temperatures of the cycle, and it is true that the reversed Carnot cycle is the most efficient refrigeration cycle operating between these two specified temperature levels.

Question 53

The number of degrees of freedom for an azeotropic mixture in a two component vapour-liquid equilibria is/are

Answer 53

1
Degree of freedom = C−∅+2

For azeotropic binary mixture since number of components(c)=2

Number of phases(∅)=2

Degree of freedom =2

But for azeotropic mixture since vapor composition =
liquid composition
Degree of freedom becomes =1
We will use equation F = C-P+2-r-s.
r = No. of reaction in system
s = Specialty constant

Here s=1 because of azeotropic solution,
So F = 2 - 2 + 2-1,
F = 1.

Question 54

Any substance above its critical temperature exists as

Answer 54

Above the critical temperature and pressure, a substance exists as a dense fluid called a supercritical fluid, which resembles a gas in that it completely fills its container but has a density comparable to that of a liquid

Question 55

Which of the following decreases with increase in pressure ?
Melting point of ice
Melting point of wax
Boiling point of liquids
none of these

Answer 55

Melting point of ice

Question 56

(1/V)(partial derivative of V over partial derivative ofT ) at constant P is the mathematical expression

Answer 56

co-efficient of thermal expansion

Thermal Expansion of Gases No tables of coefficients of thermal
expansion of gases are given in this edition. The coefficient at constant pressure,
1/u (∂u/∂T)p, for an ideal gas is merely the reciprocal of the absolute
temperature. For a real gas or liquid, both it and the coefficient at constant
volume 1/p (∂p/∂T)v
should be calculated either from the equation of state
or from tabulated PVT data

Question 57

In case of steady flow compression polytropic process (PVn = constant), the work done on air is the lowest, when
n = y = 1.4
n = 0
n = 1
n = 1.66

Answer 57

N=1 isothermal
In case of compression, isothermal has lower work than adiabatic and vice-versa in case of expansion.
Area under p−v
diagram is minimum when work is done on a system under isothermal conditions hence n=1.

Question 58

A liquid under pressure greater than its vapour pressure for the temperature involved is called a __________ liquid.
subcooled
saturated
non-solidifiable
none of these

Answer 58

Subcooled

Question 59

For a real gas, the chemical potential is given by

Answer 59

RT dlnf

We know the property relation dG=VdP−sdT
for constant temperature dT=0

For an ideal gas
dG=VdPdG=RTPdP⇒dG=RTdlnP

For a real gas also if we want to describe the relation in the same functional form we express it as dG=RTdlnf⇒dμ=RTdlnf
where f=
fugacity, that means we buried the entire non ideality in this term fugacity. The term fugacity is also called as effective pressure.

Question 60

At absolute zero temperature, all substances have the same

Answer 60

Heat capacity
Definition of heat capacity: the amount of heat required to raise the temperature of a substance or material by a small amount is called heat capacity.

limdT→0dQ=C(heat capacity)

Every substance has its own molecules and every molecule in a substance has its own properties and structure depending on the nature of the substance so different molecules exhibit different heat capacity at the same temperature. But every substance molecules at 0K will come to rest and to raise the temperature of a substance by a negligible amount doesn’t depend upon the nature of the substance but once the substance reaches dT
amount of temperature different substance or materials exhibit different heat capacity.

Question 61

Lowering of condenser temperature (keeping the evaporator temperature constant) in case of vapour compression refrigeration system results in
increased COP.
same COP.
decreased COP.
increased or decreased COP ; depending upon the type of refrigerant

Answer 61

increased COP.
Condenser tem T1 > evaporation T2.
COP Refrigeration= T2/(T1 - T2).
If T1 decreased COP increased.

Question 62

Pick out the correct statement.
If an insoluble gas is passed through a volatile liquid placed in a perfectly insulated container, the temperature of the liquid will increase.
A process is irreversible as long as Δ S for the system is greater than zero.
The mechanical work done by a system is always equal to P.dV.
The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants.

Answer 62

The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants.

Question 63

Grams of butane (C4H10) formed by the liquefaction of 448 litres of the gas (measured at (STP) would be
580
640
1160
data insufficient; can’t be computed

Answer 63

1160
58/22.4 = 2.58,
2.58*448 = 1160.
Lets take ideal gas equation.

pv=nrt.

We know n = no of moles = weight(w)/molecular weight(m)
substitute n = w/m in ideal gas equation.
at stp T= 273k.
P= 101325.
given v = 448 liters = 0.448m3.
R = 8.314.
m = molecular weight of butane 58,
substitute all above values,
(1013250.44858) / (8.314*273).
We get w = 1159.9 gm.

Question 64

The thermodynamic law, PVy
^y = constant, is not applicable in case of
ideal compression of air.
free expansion of an ideal gas.
adiabatic expansion of steam in a turbine.
adiabatic compression of a perfect gas.

Answer 64

Free expansion of an ideal gas
For free/joule expansion W=Q=0 can’t be plotted on P-V dia.

Question 65

What is the value of maximum COP in case of absorption refrigeration, if refrigeration provided is at temperature, TR(where, T1 and T2 are source & surrounding temperatures respectively.)?

Answer 65

(Tr/T2-Tr)[(T1-T2)/T1]

Question 66

Mollier diagram is a plot of

Answer 66

entropy vs. enthalpy

Question 67

Partial der of E over partial der of T at constant V is mathematical expression for

CV
enthalpy change
free energy change
none of these

Answer 67

None of these
But if partial der of U Yung numerator then cv siya

Question 68

Also known as residual properties

Answer 68

Departure function

Question 69

Range of efficiency of turbine and compressor

Answer 69

0.7 to 0.8

Question 70

Bij

Answer 70

Cross coefficient(mixture)
Bii or bjj virial coefficient of pure species

Question 71

Exponential term in condesed phases calculation of saturation fugacity

Answer 71

Poynting correction

Question 72

bρ

Answer 72

Packing fraction

Question 73

Used in petroleum and natural gas industries for light hydrocarbons and a few other commonly encountered gases.

Answer 73

Extended virial eqns with 8 parameters all functions of compositions introduced by Webb, Benedict and Rubin

Question 74

Interaction parameter a sub ij is often evaluated from pure species by a geometric mean combining rule

Answer 74

Lorenz berthelot rule

Question 75

Theory for associating molecules
Also implemented to achieve smooth transition between cubic eqns and an association model

Answer 75

Wertheim’s theory

Question 76

Superior to cubic eqns for mixtures involving molecules with high molecular weights above about 1200 g/mol

Answer 76

SAFT model statistical associating fluid theory