# Thermodynamics Questions and Answers – Ideal Gas-1

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Ideal Gas-1”.

1. An ideal gas is one which obeys the law pv=RT at all pressures and temperatures.
a) true
b) false

Explanation: Though such a gas is hypothetical.

2. The value of universal gas constant is
a) 8.2353
b) 8.3143
c) 8.5123
d) none of the mentioned

Explanation: This value comes from the Avogadro law when we put p=760 mm Hg = 1.013*10^5 N/m^2 , T=273.15 K , v=22.4 m^3/kgmol.

3. Which of the following statement is true?
a) characteristic gas constant is given by dividing the universal gas constant by the molecular weight
b) Avogadro’s number (A) = 6.023 * 10^26 molecules/kgmol
c) Boltzmann constant (K) = 1.38 * 10^-23 J/molecule K
d) all of the mentioned

Explanation: The Boltzmann constant is given by universal gas constant divided by Avogadro number.

4. The equation of state of an ideal gas is given by
a) pV=mRT, here R is characteristic gas constant
b) pV=nRT, here R is universal gas constant
c) pV=NKT
d) all of the mentioned

Explanation: Characteristic gas constant is given by dividing the universal gas constant by the molecular weight and Boltzmann constant is given by universal gas constant divided by Avogadro number.

5. Specific heats are constant for an ideal gas.
a) true
b) false

Explanation: For an ideal gas, specific heats are constant and it satisfies the equation of state.

6. For real gases,
a) specific heats vary appreciably with temperature
b) specific heats vary little with pressure
c) both of the mentioned
d) none of the mentioned

Explanation: This is in contrast to an ideal gas for which specific heats are constant.

7. At constant temperature, (u being the internal energy)
a) u change when v or p changes
b) u does not change when v or p changes
c) u does not change when t changes
d) u always remains constant

Explanation: Internal energy does not change with change in v or p but changes only when temperature changes.

8. For an ideal gas, internal energy is a function of temperature only.
a) true
b) false

Explanation: This is known as Joule’s law.

9. Which of the following statement is true? (c is the specific heat at constant volume)
a) the equation du=c*dT holds good for an ideal gas for any process
b) for gases other than ideal ones, the equation holds true for a constant volume process only
c) for an ideal gas c is constant and hence Δu=c*ΔT
d) all of the mentioned

Explanation: All these statements are true and also internal energy is a function of temperature only.

10. Which of the following statement is correct for an ideal gas?
a) h=u+pv
b) h=u+RT
c) h=f(T)
d) all of the mentioned

Explanation: For an ideal gas, pv=RT and hence h is a function of temperature only.

11. Characteristic gas constant is given by (here cp=specific heat at constant pressure and cv is the specific heat at constant volume)
a) R=cv – cp
b) R=cp + cv
c) R=cp – cv
d) none of the mentioned

Explanation: Δh=(cv+R)ΔT = cp*ΔT.

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