# Thermodynamics MCQs practice test | thermodynamics mcqs with answers – Mechanicaltalks

Below are given some most important MCQs of thermodynamics. These are very useful in examination point of view and will be really helpful in upcoming exams. Read every questions and try to answer them from your own.

Q1. Boyle’s law states that change of internal energy of a perfect gas is directly proportional to the change of temperature

(a) Agree
(b) Disagree
Disagree

Q2. The absolute perssure of a given mass of a perfect gas varies inversely as its volume, when the temperature remains constant. This statement is known as Charles law
(a) Yes
(b) No

-No

Q3. Charles law states that all perfect gases change in volume by ___ of its original volume at 0°C for every 1°C change in temperature, when pressure remains constant.
(a) 1/27th
(b) 1/173th
(c) 1/273th
(d) 1/93th.

-1/273th

Q4. The absolute zero pressure can be attained at a temperature of
(a) 0°C
(b) 273°C
(c) 273°K
(d) none of these.

-none of these

Q5. The general gas equation is
(a) pv = mRT
(b) pv = RT
(c) pv^m = C
(d) pv = RT^m
where P- Pressure, v Volume, m = mass, T= Absolute temperature, and R = Gas constant.

-pv = mRT

Q6. The value of gas constant (R) in S. I. units is
(a) 0.287 J/kg K
(b) 2.87 J/kg K
(c) 28.7 J/kg K
(d) 287 J/kg K.

-287 J/kg K.

(a) the product of the gas constant and the molecular mass of an ideal gas is constant (b) the sum of partial pressure of the mixture of two gases is sum of the two
(c) equal volumes of all gases, at the same temperature and pressure, contain equal number of molecules
(d) all of the above.

-equal volumes of all gases, at the same temperature and pressure, contain equal number of molecules

Q8. The molecular mass expresssed in gram (e.i. 1g-mole) of all gases, at N. T. P., occupies a volume of
(a) 0.224 litres
(b) 2.24 litres
(c) 22.4 litres
(d) 224 litres.

-22.4 litres

Q9. Which of the following gas has a minimum molecular mass
(a) Oxygen
(b) Nitrogen
(c) Hydrogen
(d) Methane.

-Hydrogen

Q10. According to Avogadro’s law, the density of any two gases is __their molecular masses, if the gases are at the same temperature and pressure.
(a) equal to
(b) directly proportional to
(e) inversely proportional to

-directly proportional to

Q11. The universal gas constant (or molar constant) of a gas is the product of
(a) molecular mass of the gas and the gas constant
(b) atomic mass of the gas and the gas constant
(c) molecular mass of the gas and the specific heat at constant pressure
(d) molecular mass of the gas and the specific heal at constant volume.

-molecular mass of the gas and the gas constant

Q12. ln S.I. units, the value of the universal gas constant is
(a) 831.4 J/kg mole-K
(b) 8.314 J/kg mole-K
(c) 83.14 J/kg mole-K
(d) 8314 J/kg mole-K

-8314 J/kg mole-K

Q13. The value of universal gas constant is same for all gases.
(a) Yes
(b) No

-Yes

Q14. The amount of heat required to raise the temperature of the unit mass of gas through one degree at constant volume, is called
(a) specific heat at constant volume
(b) kilo Joule
(c) specific heat at constant pressure
(d) none of these.

-specific heat at constant volume

Q15. The amount of heat required to raise the temperature of unit mass of a gas through one degree at constant pressure is called specific heat at constant pressure.
(a) True
(b) False

-True

Q16. The amount of heat required to raise the temperature of 1 kg of water through one Kelvin is called
(a) specific heat at constant volume
(b) specific heat at constant pressure
(c) kilo-Joule
(d) none of these.

-kilo-Joule

Q17. The specific heat at constant volume is
(a) the amount of heat required to raise the temperature of unit mass of gas through
one degree, at constant pressure
(b) the amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume
(c) the amount of heat required to raise the temperature of 1 kg of water through one degree
(d) any one of the above.

-the amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume

Q18. The value of specific heat at constant pressure is __ that of at constant volume
(a) less than
(b) equal to
(c) more than

-more than

Q19. When the gas is heated at constant volume, the heat supplied
(a) increases the internal energy of the gas
(b) increases the temperature of the gas
(c) does some external work during expansion
(d) all of these.

-(a) and (b) both

Q20. When the gas is heated at constant pressure, the heat supplied
(a) increases the internal energy of the gas

(b) increases the temperature of the
(c) does some external work during expansion
(d) all of these.

-(b) and (c) both

Q21. The universal gas constant of a gas is the product of molecular mass of the gas and the gas constant
(a) Correct
(b) Incorrect

-Correct

Q22. The amount of heat required to raise the temperature of __ water through one degree is called kilojoule.
(a) 1g
(b) 10g
(c) 1000g
(d) 100 g

-1000g

Q23. When the gas is heated at constant volume, the heat supplied increases the internal energy of the gas.
(a) True
(b) False

-True

Q24. The ratio of specific heat at constant pressure (cp) and specific heat at constant volume (cv) is always __ one.
(a) equal to
(b) less than
(c) greater than

-greater than

Q25. When a gas is heated at constant volume
(a) its temperature will increase
(b) its pressure will increase
(c) both temperature and pressure will increase
(d) neither temperature nor pressure will increase.

-both temperature and pressure will increase

Q26. When a gas is heated at constant pressure
(a) its temperature will increase
(b) its volume will increase
(c) both temperature and volume will increase
(d) neither temperature not volume will increase.

-both temperature and volume will increase

Q27. The heating of gas at constant volume is governed by
(a) Boyle’s law
(b) Charles’ law
(c) Gay-Lussac law

-Gay-Lussac law

Q28. The heating of a gas at constant pressure is governed by
(a) Boyle’s law
(b) Charles’ law
(c) Gay-Lussac law

-Charles’ law

Q29. When gas is heated at constant pressure, the heat supplied is utilised in
(a) increasing the internal energy of gas
(b) doing some external work
(c) increasing the internal energy of gas and also for doing some external work
(d) none of the above.

-increasing the internal energy of gas and also for doing some external work

Q30. A mixture of gas expands from 0.03 m³ to 0.06 m³ at a constant pressure of 1MPa and absorbs 84 kJ of heat during the process. The change in internal energy of the mixture is
(a) 30 kJ
(b) 54 kJ
(c) 84 kJ
(d) 114 kJ.

-54 kJ

Q31. The gas constant (R) is equal to __ the of two specific heats
(a) sum
(b) difference
(c) product
(d) ratio.

-difference

Q32. The heating and expanding of a gas is called thermodynamic system.
(a) Yes
(b) No.

-No

Q33. When the gas is cooled at constant pressure
(a) its temperature increases but volume decreases
(b) its volume increases but temperature decreases
(c) both temperature and volume increases
(d) both temperature and volume decreases.

-both temperature and volume decreases

Q34. A process, in which the gas is heated or expanded in such a way that the product of its pressure and volume remains constant, is called
(a) isothermal process
(b) hyperbolic process
(d) polytropic process.

-hyperbolic process

Q35. The hyperbolic pocess is governed by
(a) Boyle’s law
(b) Charles’ law
(c) Gay-Lussac law

-Boyle’s law

Q36. A process, in which the temperature of the working substance remains constant during its expansion or compression, is called
(a) isothermal process
(c) hyperbolic process
(d) polytropic process.

-isothermal process

Q37. The workdone in a free expansion process is zero
(a) True
(b) False.

-True

Q38. In a steady flow process, the ratio of (a) heat transfer is constant
(b) work transfer is constant
(c) mass flow at intet and outlet is same
(d) all of these.

-all of these

Q39. The throttling process is an irreversible steady flow expansion process.
(a) Correct
(b) Incorrect.

-Correct

Q40. The area under the temperature-entropy curve (T- s curve) of any thermodynamic process represents
(a) heat absorbed
(b) heat rejected
(c) either (a) or (b)
(d) none of these.

-either (a) or (b)

Q41. The change of entropy, when heat is removed from the gas, is positive
(a) Yes
(b) No.

-No

Q42. The property of a working substance which increases or decreases as the heat is supplied or removed in a reversible manner, is known as
(a) enthalpy
(b) internal energy
(c) entropy
(d) external energy.

-entropy

Q43. The entropy may be expressed as a function of
(a) pressure and temperature
(b) heat and work
(c) temperature and volume
(d) all of these.

-pressure and temperature

Q44. The heat absorbed or rejected by the working substance is given by
(a) dQ = T.ds
(b) dQ0-T /ds
(c) dQ=ds/T
(d) none of these.
ds = Increase or decrease of entropy,
T = Absolute temperature
dQ = Heat absorbed or rejected.

-dQ = T.ds

Q45. The entropy of water at 0° C is assumed to be
(a) 1
(b) 0
(c) -1
(d) 10.

-0

Q46. The increase in entropy of a system represents
(a) increase in availability of energy
(b) Increase in temperature
(c) decrease in pressure

Q47. The area under the temperature-entropy curve (i.e. T-s curve) of any thermodynamic process represents the workdone during the process.
(a) Agree
(b) Disagree.

-Disagree.

Q48. The change of entropy, when heat is absorbed by the gas, is
(a) positive
(b) negative
(c) positive or negative.

-positive

Q49. The entropy is a point function and thus it is a property of the same.
(a) Correct
(b) Incorrect.

-Correct

Q50. The entropy __ in an irreversible cyclic process.
(a) remains constant
(b) decreases
(c) increases.

-increases.

That was some most important MCQs of thermodynamics. This will help a lot for the competitive examinations. If you like this content then do share this with your well wishers. If you have any doubts regarding any mechanical engineering topic, then let us know in comment section or contact us through email.