Indiabix - Thermodynamics Flashcards
Maximum work that could be secured by expanding the gas over a given pressure range is the __________ work.
isothermal
Internal energy change of a system over one complete cycle in a cyclic process is
zero
Van Laar equation deals with the activity co-efficients in
binary solutions
Entropy is a measure of the __________ of a system.
disorder
A refrigerator may be termed as a
heat pump
Out of the following refrigration cycles, which one has the minimum COP (Co-efficient of performance)?
Air cycle
No work is done by the system, when a reaction occurs at constant
volume
The freezing point of a liquid decreases when the pressure is increased, if the liquid __________ while freezing.
contracts
“At the absolute zero temperature, the entropy of every perfectly crystalline substance becomes zero”. This follows from the
third law of thermodynamics
During Joule-Thomson expansion of gases
enthalpy remains constant.
Degress of freedom at triple point will be
0
“Law of corresponding states” says that
two different gases behave similarly, if their reduced properties (i.e. P, V and T) are same.
Linde gas liquefaction process employs cooling
by throttling
Equilibrium constant decreases as the temperature
increases, for an exothermic reaction.
The expression, (1) , gives the free energy change
with pressure changes at constant temperature.
In jet refrigerators, the refrigerating fluid is practically always
water
Water on heating from 1 to 4°C
contracts
Partial molar free energy of an element A in solution is same as its
chemical potential
Free energy change at equilibrium is
zero
The temperature at which both liquid and gas phases are identical, is called the __________ point.
critical
What is the value of ln y (where y = activity co-efficient) for ideal gases ?
Zero
The partial pressure of each constituent present in an alloy is __________ the total vapor pressure exerted by the alloy.
less than
Which of the following decreases with increase in pressure ?
Melting point of ice
A liquid under pressure greater than its vapour pressure for the temperature involved is called a __________ liquid.
subcooled
At absolute zero temperature, all substances have the same
heat capacity
Lowering of condenser temperature (keeping the evaporator temperature constant) in case of vapour compression refrigeration system results in
increased COP.
When a gas in a vessel expands, its internal energy decreases. The process involved is
reversible
Refrigeration capacity of a household refrigerator may be round about __________ tons.
0.15
The melting point of paraffin wax (which contracts on solidification) __________ with pressure rise.
increases
Activity co-efficient is a measure of the
departure from ideal solution behaviour.
Kopp’s rule is used to calculate the heat capacity of
solids
In an ideal solution, the activity of a component equals its
mole fraction.
Clayperon equation deals with the
rate of change of vapour pressure with temperature.
The absolute entropy for all crystalline substances at absolute zero temperature is
zero
Forward reaction will be favoured for the exothermic reaction, represented by CO + H2O ⇌ CO2 + H2, by
low temperature and high pressure.
Enthalpy of a gas depends upon its
temperature
Fugacity is most helpful in
representing actual behaviour of real gases.
A cyclic engine exchanges heat with two reservoirs maintained at 100 and 300°C respectively. The maximum work (in J) that can be obtained from 1000 J of heat extracted from the hot reservoir is
349
In the equation, PV^n = Constant, if the value of n = 0, then it represents a reversible __________ process.
isobaric
Near their critical temperatures, all gases occupy volumes __________ that of the ideal gas.
less than
What is the number of degrees of freedom for liquid water in equilibrium with a mixture of nitrogen and water vapor ?
2
All gases above its inversion temperature, in a throttling process will show
a heating effect.
First law of thermodynamics is mathematically stated as
dQ = dE + dW
Translational kinetic energy of molecules of an ideal gas is proportional to (where, T = absolute temperature of the gas )
T
Equation which relates pressure, volume and temperature of a gas is called the
equation of state
The temperature at which a real gas obeys the ideal gas laws over a wide range of pressure is called __________ temperature.
Boyle
The expression, nCv(T2 - T1), is for the __________ of an ideal gas.
work done under adiabatic condition
Which of the following is a widely used refrigerant in vapour compression refrigeration system (using large centrifugal compressor)?
Freon
Internal energy is equal to the heat absorbed in case of a/an __________ process.
constant volume
The first law of thermodynamics is a restatement of the law of conservation of
mass
In an adiabatic process, the
heat transfer is zero.
A nozzle is a device, which
increases kinetic energy and decreases pressure.
The work done in an adiabatic change in a particular gas depends upon changes in the __________ only.
temperature
Number of degrees of freedom for a three phase system in equilibrium comprising of three non-reacting chemical species is
2
Critical solution temperature (or the con-solute temperature) for partially miscible liquids (e.g., phenol-water) is the minimum temperature at which
a homogeneous solution (say of phenol water) is formed.
__________ functions are exemplified by heat and work.
Path
The entropy change in a reversible isothermal process, when an ideal gas expands to four times its initial volume is
R loge 4
Pick out the wrong statement.
A refriferation cycle violates the second law of thermadynamics.
The equation, PV = nRT, is best obeyed by gases at
low pressure & high temperature.
Internal energy of an element at 1 atm and 25° C is __________ kcal/kg.mole.
0
Which of the following liquid metals has the highest thermal conductivity ?
Molten sodium
Which of the following has the least thermal efficiency ?
Steam engine
Number of components (C), phase (P) and degrees of freedom (F) are related by Gibbs phase rule as
P + F - C = 2
The value of Cp & Cv respectively for monoatomic gases in Kcal/kg Mole . °K are
5 & 3
During a reversible isothermal expansion of an ideal gas, the entropy change is
+ve
Those solutions in which there is no volume change upon mixing the components in the liquid state and which, when diluted do not undergo any heat change (i.e. heat of dilution is zero), are called __________ solutions.
ideal
The compressibility factor of a gas is given by (where, V1 = actual volume of the gas V2 = gas volume predicted by ideal gas law )
V1/V2
“If different processes are used to bring about the same chemical reaction, the enthalpy change is same for all of them”. This is __________ law.
Hess’s
Fugacity is a measure of the
escaping tendencies of the same substance in different phases of a system.
The quantitative effect of temperature on chemical equilibrium is given by the
Vant-Hoff equation.
For an irreversible process involving only pressure-volume work
(dF)T, p <0
The enthalpy change when ammonia gas is dissolved in water is called the heat of
solution
Critical compressibility factor for all substances
are more or less constant (vary from 0.2 to 0.3).
For a given substance at a specified temperature, activity is __________ to fugacity.
directly proportional
In case of vapour compression refrigeration system, elevating the evaporator temperature (keeping the condenser temperature constant) results in
enhanced COP.
As the temperature is lowered towards the absolute zero, the value of the quantity approaches
zero
In case of a reversible process (following pv^n = constant), work obtained for trebling the volume (v1 = 1 m^3 and v2 3 m^3 ) is max imum, when the value of ‘n’ is
0
The Carnot co-efficient of performance (COP) of a domestic air conditioner compared to a household refrigerator is
less
The unit of fugacity is the same as that of the
pressure
The total change in the enthalpy of a system is independent of the
number of intermediate chemical reactions involved.
Vapour which is at a pressure smaller than the saturation pressure for the temperature involved is called a __________ vapour.
superheated
At equilibrium condition, the chemical potential of a material in different phases in contact with each other is equal. The chemical potential for a real gas (μ) is given by(where, μ = standard chemical potential at unit fugacity (f° = 1 atm.) and the gas behaves ideally.)
μ° + RT ln f
Which of the following is not an intensive property ?
Volume
With increase in pressure (above atmospheric pressure), the Cp of a gas
increases
A change in state involving a decrease in entropy can be spontaneous, only if
it is exothermic.
Joule-Thomson co-efficient which is defined as, (1) , changes sign at a temperature known as inversion temperature. The value of Joule-Thomson co-efficient at inversion temperature is
0
Heat is added at constant temperature in an ideal __________ cycle.
Stirling
Pick out the correct equation relating ‘F’ and ‘A’.
F = A + PV
In a reversible process
Tds = dE + dW
With increase in compression ratio, the efficiency of the otto engine
increases
Refrigerants commonly used for domestic refrigerators are
ethyl chloride or methyle chloride
Heat of formation of an element in its standard state is
0
The shape of T-S diagram for Carnot Cycle is a
rectangle
In the equation, PVn = constant, if the value of n = 1, then it represents a reversible __________ process.
isothermal
Which of the following non-flow reversible compression processes require maximum work ?
Adiabatic process
“When a system in equilibrium is subjected to a change in temperature, pressure or concentration, the equilibrium is displaced in a direction which tends to undo the effect of the change.” This is called the
Le-Chatelier principle.
Sound waves propagation in air exemplifies an __________ process.
adiabatic
For equilibrium process (i.e. reversible) in an isolated system
ds = 0
With increase in reduced temperature, the fugacity co-efficient of a gas at constant reduced pressure
increases
Efficiency of a heat engine working on Carnot cycle between two temperature levels depends upon the
two temperatures only.
In Joule-Thomson porous plug experiment, the
enthalpy does not remain constant.
A Carnot cycle consists of the following steps :
Two isothermals and two isentropics.
For a cyclic process, a fixed ratio between heat and work
always exists
In vapour compression refrigeration system, if the evaporator temperature and the condenser temperatures are -13°C and 37°C respetively, the Carnot COP will be
5.2
Which of the following is an extensive property of a system ?
Heat capacity
The reaction A (l) → R(g) is allowed to reach equilibrium conditions in an autoclave. At equilibrium, there are two phases, one a pure liquid phase of A and the other a vapor phase of A, R and S. Initially A alone is present. The number of degrees of freedom are
1
Cp - Cv = R is valid for __________ gases.
ideal
Melting of wax is accompanied with __________ in entropy.
increase
Tea kept in a thermos flask is vigorously shaken. If the tea is considered as a system, then its temperature will
increase
After throttling, gas temperature
decreases
When liquid and vapour phase of multi-component system are in equilibrium (at a given temperature and pressure), then chemical potential of each component is
same in both the phases.
On opening the door of an operating refrigerator kept in a closed room, the temperature of the room will
increase
Gibbs-Duhem equation
states that n1dμ1 + n2dμ2 + ….njdμj = 0, for a system of definite composition at constant temperature and pressure.
The internal energy of an ideal gas does not change in a reversible __________ process.
isothermal
For an ideal gas, the chemical potential is given by
RT dlnP
Two substances are in equilibrium in a reversible chemical reaction. If the concentration of each substance is doubled, then the value of the equilibrium constant will be
same
Heat requirement for decomposition of a compound into its elements is __________ that is evolved during the formation of that compound from its elements.
the same
Which of the following equations is obtained on combining 1st and 2nd law of thermodynamics, for a system of constant mass?
dE = Tds - PdV
The efficiency of a Carnot heat engine operating between absolute temperatures T1 and T2 (when, T1 > T2) is given by (T1 - T2)/T1. The co-efficient of performance (C.O.P.) of a Carnot heat pump operating between T1 and T2 is given by
T1/(T1-T2)
Throttling (Joule-Thomson effect) process is a constant __________ process.
enthalpy
Boiling of liquid is accompanied with increase in the
vapor pressure.
Change of state namely evaportation condensation, freezing and melting is an __________ process.
isothermal
With increase in temperature, the internal energy of a substance
increases
It is desired to bring about a certain change in the state of a system by performing work on the system under adiabatic conditions.
The amount of work needed is path dependent.
For organic compounds, group contribution method can be used for the estimation of
critical properties.
What happens in a reversible adiabatic compression ?
Heating occurs
The efficiency of an Otto engine compared to that of a diesel engine, for the same compression ratio will be
more
Isotherm on an enthalpy-concentration diagram, for an ideal solution will be a
straight line
A cylinder contains 640 gm of liquid oxygen. The volume occupied (in litres) by the oxygen, when it is released and brought to standard conditions (0°C, 760 mm Hg) will be __________ litres.
448
Dryness fraction of wet steam is defined as the ratio of mass of vapour in the mixture to the mass of mixture __________ calorimeter is not used for measuring the dryness fraction of steam.
Bomb
As the time is passing, entropy of the universe
is increasing
Which of the following processes can not be made reversible even under ideal condition of operation?
Free expansion of a gas.
The relation connecting the fugacities of various components in a solution with one another and to composition at constant temperature and pressure is called the __________ equation.
Gibbs-Duhem
With increase in temperature, the atomic heat capacities of all solid elements
increases
The temperature at the eutectic point of the system is the __________ temperature that can be attained in the system.
lowest
Steam undergoes isentropic expansion in a turbine from 5000 kPa and 400°C (entropy = 6.65 kJ/kg K) to 150 kPa) (entropy of saturated liquid = 1.4336 kJ/kg . K, entropy of saturated vapour = 7.2234 kJ/kg. K) The exit condition of steam is
superheated vapour.
An isentropic process is carried out at constant
volume
The necessary condition for phase equilibrium in a multiphase system of N components is that the
chemical potentials of a given component should be equal in all phases.
Compressibility factor-reduced pressure plot on reduced co-ordinates facilitates
use of only one graph for all gases.
Pick out the wrong statement.
At constant pressure, solubility of a gas in a liquid diminishes with rise in temperature.
Reduced pressure of a gas is the ratio of its
pressure to critical pressure.
Air enters an adiabatic compressor at 300K. The exit temperature for a compression ratio of 3, assuming air to be an ideal gas (Y = Cp/Cv = 7/5) and the process to be reversible, is
300(32/7)
An ideal monoatomic gas is taken round the cycle ABCDA as shown below in the P-V diagram (1) The work done during the cycle is
PV
Third law of thermodynamics is concerned with the
value of absolute entropy.
Claude’s liquefaction process employs the cooling of gases by
expansion in an engine
The molar excess Gibbs free energy, g^E, for a binary liquid mixture at T and P is given by, (g^E/RT) = A . x1. x2, where A is a constant. The corresponding equation for ln y1, where y1 is the activity co-efficient of component 1, is
A . X2^2
There is a change in __________ during the phase transition.
volume
First law of thermodynamics deals with the
direction of energy transfer.
A solute distributes itself between two non-miscible solvents in contact with each other in such a way that, at a constant temperature, the ratio of its concentrations in two layers is constant, irrespective of its total amount”. This is
the distribution law.
A solid is transformed into vapour without going to the liquid phase at
triple point
Standard temperature and pressure (S.T.P.) is
0°C and 750 mm Hg
Charles’ law for gases states that
V/2 = Constant
If heat contents of CH4, C2H4 and C3H8 are -17.9, 12.5 and -24.8 kcal/mole respectively, than ΔH for the reaction CH4(g) + C2H4(g) C3H8(g) will be __________ Kcal.
-19.4
At 60° C, vapour pressure of methanol and water are 84.562 kPa and 19.953 kPa respectively. An aqueous solution of methanol at 60° C exerts a pressure of 39.223 kPa; the liquid phase and vapour phase mole fractions of methanol are 0.1686 and 0.5714 respectively. Activity co-efficient of methanol is
1.572
Gases are cooled in Joule-Thomson expansion, when it is __________ inversion temperature.
below
Which of the following behaves most closely like an ideal gas ?
He
When a system is in equilibrium for all possible processes, the differential or finite change of entropy is
< 0
Degree of freedom of the system ice-water-vapour will be
0
The third law of thermodynamics states that the
heat capacity of a crystalline solid is zero at absolute zero temperature.
In the decomposition of PCl5 represented by, PCl5 ⇌ PCl3 + Cl2, decrease in the pressure of the system will __________ the degree of dissociation of PCl5.
increase
Trouton’s ratio is given by (where λb, = molal heat of vaporisation of a substance at its normal boiling point, kcal/kmol Tb = normal boiling point, °K )
λb/Tb
Compound having large heat of formation is
more stable.
Heating of water under atmospheric pressure is an __________ process.
isobaric
Solubility of a substance which dissolves with an increase in volume and liberation of heat will be favoured by the
low pressure and low temperature.
For a stable phase at constant pressure and temperature, the fugacity of each component in a binary system __________ as its mole fraction increases.
increases
Measurement of thermodynamic property of temperature is facilitated by __________ law of thermodynamics.
zeroth
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
-RT ln 0.5
Keeping the pressure constant, to double the volume of a given mass of an ideal gas at 27°C, the temperature should be raised to __________ °C.
327
Isobaric process means a constant process.
pressure
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
Clayperon-Claussius equation
The accentric factor of a materical, ‘ω’, is defined as ω = -log10(Pr^sat)Tr^-1 = 0.7, where, Pr^sat = reduced vapor pressure, Tr = reduced temperature. The value of accentric factor is always
< 1
Boyle’s law for gases states that
(1) , when temperature & mass of the gas remain constant.
Out of the following refrigeration cycles, which one has maximum COP ?
Carnot cycle
Pick out the correct statement:
Under reversible conditions, the adiabatic work is less than isothermal work.
All gases during throttling process at atmospheric temperature and pressure show a cooling effect except
H2
Compressibility factor for almost all the gases are approximately same at the same
reduced pressure and reduced temperature.
Pick out the correct statement.
Efficiency of an Otto engine is higher than that of a diesel engine for the same compression ratio.
A closed system is cooled reversibly from 100°C to 50°C. If no work is done on the system
U and S both decreases
Pick out the wrong statement.
The heat capacity of solid inorganic substance is exactly equal to the heat capacity of the substance in the molten state.
The number of degrees of freedom for an azeotropic mixture in a two component vapour-liquid equilibria is/are
one
For a real gas, the chemical potential is given by
RT dlnf
The thermodynamic law, PVy = constant, is not applicable in case of
free expansion of an ideal gas.
Specific heat of a gas for a reversible adiabatic process is
zero
A system is said to be isopiestic, if there is no __________ change.
pressure
The unity of Planck’s constant ‘h’ in the equation, E = hv is
J.S
Co-efficient of Performance (COP) of a refrigerator is the ratio of the
refrigeration obtained to the work required.
A solid metallic block weighing 5 kg has an initial temperature of 500°C. 40 kg of water initially at 25°C is contained in a perfectly insulated tank. The metallic block is brought into contact with water. Both of them come to equilibrium. Specific heat of block material is 0.4 kJ.kg^-1. K^-1. Ignoring the effect of expansion and contraction and also the heat capacity to tank, the total entropy change in kJ.kg^-1 , K^-1 is
0
dW and dq are not the exact differential, because q and W are
path functions
Melting of ice exemplifies a/an
endothermic reaction.
At __________ point, all the three phases (i.e.solid, liquid and gas) co-exist.
triple
__________ explains the equilibrium constant for any chemical reaction.
Law of mass action
The standard Gibbs free energy change of a reaction depends on the equilibrium
temperature
A gas has a volume of 27.3 c.c. at 0°C. Its volume at 10°C (if pressure remains unchanged) will be __________ c.c.
28.3
Which of the following is an undesirable characteristics of a refrigerant ?
It should have a sub-atmospheric vapor pressure at the temperature in refrigerator coils.
