# Thermodynamics Questions and Answers – Equations of State

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Equations of State”.

1. For the ideal gas equation, what assumptions are made?
a) there is little or no attraction between the molecules of the gas
b) the volume occupied by the molecules is negligibly small compared to the volume of the gas
c) both of the mentioned
d) none of the mentioned

Explanation: The ideal gas equation pv=RT is established from the postulates of the kinetic theory of gases considering these two assumptions.

2. When does a real gas obey the ideal gas equation closely?
a) at high pressure and low temperature
b) at low pressure and high temperature
c) at low pressure and temperature
d) at high pressure and temperature

Explanation: At low pressure and high temperature, the intermolecular attraction and the volume of the molecules compared to the total volume of the gas are not of much significance.

3. The real gases deviate from the ideal gas equation when the pressure increases.
a) true
b) false

Explanation: With increase in pressure, the intermolecular forces of attraction and repulsion increase, and also the volume of the molecules becomes appreciable compared to the gas volume.
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4. The corrected gas equation is given by
a) (p+a/(v2))(v+b)=RT
b) (p-a/(v2))(v-b)=RT
c) (p-a/(v2))(v+b)=RT
d) (p+a/(v2))(v-b)=RT

Explanation: The two correction terms were introduced by van der Waals.

5. Which of the following statement is true about the correction terms?
a) the coefficient a was introduced to account for the existence of mutual attraction between the molecules
b) the term a/(v2) is called the force of cohesion
c) the coefficient b was introduced to account for the volumes of the molecules and is known as co-volume
d) all of the mentioned

Explanation: These coefficients were also introduced by van der Waals.

6. Real gases conform more closely with the van der Waals equation of state than the ideal gas equation of state.
a) true
b) false

Explanation: This happens particularly at higher pressures.

7. The following also gave two-constant equations of state.
a) Berthelot
b) Dieterici
c) Redlich-Kwong
d) all of the mentioned

Explanation: These are also two-constant equations of state other than the van der Waals equation.

8. Compressibility factor Z is given by
a) RT/pv
b) pv/RT
c) (RT/pv)2
d) (pv/RT)2

Explanation: This ratio is known as compressibility factor.

9. For an ideal gas, Z has the value
a) 0
b) 2
c) 1
d) infinity

Explanation: For an ideal gas, pv=RT hence Z=1.

10. The magnitude of Z at a particular pressure and temperature indicates the extent of deviation of the gas from the ideal gas behaviour.
a) true
b) false

Explanation: This is a basic fact about the compressibility factor.

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