91. A piston-cylinder device initially contains 0.4 m³ of air (to be treated as an ideal gas) at 100 kPa and 80°C. The air is now isothermally compressed to 0.1 m³. The work done during this process is ______kJ.
    (Take the sign convention such that work done on the system is negative)
    

1. 1. 55.45 kJ

   
   
   

   2. -21.45 kJ

   
   
   

   3. -55.45 kJ

   
   
   

   4. -15.45 kJ

   
   
   

---

1. View Hint View Answer Discuss in Forum

   For isothermal process
   

   W = P1V1ln		V2
   		V1

   
   

   W = 100 × 0.4 ln		0.1		= -55.45 kJ
   		0.4

   Correct Option: C

   For isothermal process
   

   W = P1V1ln		V2
   		V1

   
   

   W = 100 × 0.4 ln		0.1		= -55.45 kJ
   		0.4

---

92. The internal energy of an ideal gas is a function of
    

1. 1. temperature and pressure
      

   
   
   

   2. volume and pressure
      

   
   
   

   3. entropy and pressure
      

   
   
   

   4. temperature only

   
   
   

---

1. View Hint View Answer Discuss in Forum

   temperature only

   Correct Option: D

   temperature only

---

---

93. A mixture of ideal gases has the following composition by mass :
    

    N2	O2	CO2
    60%	30%	10%

    
    If the universal gas constant is 8314 J/kmolK, the characteristic gas constant of the mixture (in J/kgK) is _______.

1. 1. 274.996

   
   
   

   2. 247.996

   
   
   

   3. 374.996

   
   
   

   4. 174.996

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Gas constant of mixture,
   

   Rm =	Universal gas constant
   	Average molar mass

   
   

   Rm =	Universal gas constant
   	Average molar mass

   
   

   Average molar mass =	100						= 30.233 kg/kmol
   	60	+	30	+	10
   	28		32		44

   
   

   Rm =	8314	= 274.996 J/kg -K
   	30.233

   
   

   Correct Option: A

   Gas constant of mixture,
   

   Rm =	Universal gas constant
   	Average molar mass

   
   

   Rm =	Universal gas constant
   	Average molar mass

   
   

   Average molar mass =	100						= 30.233 kg/kmol
   	60	+	30	+	10
   	28		32		44

   
   

   Rm =	8314	= 274.996 J/kg -K
   	30.233

   
   

---

94. For an ideal gas with constant values of specific heats, for calculation of the specific enthalpy,
    

1. 1. it is sufficient to know only the temperature
      

   
   
   

   2. both temperature and pressure are required to be known
      

   
   
   

   3. both temperature and volume are required to be known
      

   
   
   

   4. both temperature and mass are required to be known

   
   
   

---

1. View Hint View Answer Discuss in Forum

   it is sufficient to know only the temperature
   

   Correct Option: A

   it is sufficient to know only the temperature
   

---

---

95. A frictionless piston-cylinder device contains a gas initially at 0.8 MPa and 0.015 m³. It expands quasistatically at constant temperature to a final volume of 0.030 m³. The work output (in kJ) during this process will be
    

1. 1. 8.32
      

   
   
   

   2. 12.00
      

   
   
   

   3. 554.67
      

   
   
   

   4. 8320.00

   
   
   

---

1. View Hint View Answer Discuss in Forum

   W = P1V1 ln	V2	= 8.317 kJ
   	V1

   Correct Option: A

   W = P1V1 ln	V2	= 8.317 kJ
   	V1

---