Thermodynamics (Thermo)

Q:   Which one of the following statements is correct for a superheated vapour?

• A:  Its pressure is less than the saturation pressure at a given temperature.
• B:  Its temperature is less than the saturation temperature at a given pressure.
• C:  Its volume is less than the volume of the saturated vapour at a given temperature.
• D:  Its enthalpy is less than the enthalpy of the saturated vapour at a given pressure.

Q:   An ideal gas undergoes a process from state 1 (T1 = 300 K, p1 = 100 kPa) to state 2 ( T2 = 600 K, p2 = 500 kPa). The specific heats of the ideal gas are : Cp=1kJ/kg−KandCv=0.7kJ/kg−K The change in specific entropy of the ideal gas from state 1 to state 2 (in kJ/kg−K) is ___________(correct to two decimal places).

Q:   A tank of volume 0.05 m/s3 contains a mixture of saturated water and saturated steam at 200∘C . The mass of the liquid present is 8 kg. The entropy (in kJ/kg K) of the mixture is ___________ (correct to two decimal places).
Property data for saturated steam and water are:
At 200^∘C,psat = 1.5538 MPa
vf = 0.001157 m³ /kg, vg = 0.12736 m³ /kg
sfg = 4.1014 kJ/kg K, 2.3309 sf = kJ/kg K

Q:   The molar specific heat at constant volume of an ideal gas is equal to 2.5 times the universal gas constant (8.314 J/mol K). When the temperature increases by 100 K, the change in molar specific enthalpy is ____________ J/mol.

Q:   One kg of an ideal gas (gas constant, R=400j/kg.K; specific heat at constant volume, c_v=1000j/kg.K) at 1 bar, and 300K is contained in a sealed rigid cylinder. During an adiabatic process, 100kj of work is done on the system by a stirrer. The increase in entropy of the system is ____________ J/K.

Q:   Air contains 79% N2 and 21% O2 on a molar basis. Methane (CH4) is burned with 50% excess air than required stoichiometrically. Assuming complete combustion of methane, the molar percentage of N2 in the products is ____________

Q:   One kg of an ideal gas (gas constant R = 287 J/kg·K) undergoes an irreversible process from state-1 (1 bar, 300 K) to state-2 (2 bar, 300 K). The change in specific entropy (s2 - s1)of the gas (in J/ kg·K) in the process is__________

Q:   The volume and temperature of air (assumed to be an ideal gas) in a closed vessel is 2.87 m3 and 300 K, respectively. The gauge pressure indicate by a manometer fitted to the wall of the vessel is 0.5 bar. If the gas constant of air is R = 287 J/kg·K and the atmospheric pressure is 1 bar, the mass of air (in kg) in the vessel is

• A:  1.67
• B:  3.33
• C:  5.00
• D:  6.66

Q:   Which of the following statements are TRUE with respect to heat and work?
(i) They are boundary phenomena
(ii) They are exact differentials
(iii) They are path functionss

• A:  both (i) and (ii)
• B:  both (i) and (iii)
• C:  both (ii) and (iii)
• D:  only (iii)

Q:   An ideal gas undergoes a reversible process in which the pressure varies linearly with volume. The conditions at the start (subscript 1) and at the end (subscript 2) of the process with usual notation are: p1 = 100 kPa,V1 = 0.2m3 and p2= 200 kPa,V2 = 0.1 m3 and the gas constant, R = 0.275 kJ/kg-K. The magnitude of the work required for the process (in kJ) is ________.