# Thermodynamics Questions and Answers – Evaluation of Thermodynamic Properties from an Equation of State

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This set of tricky Thermodynamics questions and answers focuses on “Evaluation of Thermodynamic Properties from an Equation of State”.

1. An equation of state can also be used to calculate internal energy, enthalpy and entropy.
a) true
b) false

Explanation: Apart form calculating volume, temperature and pressure, an equation of state can also be used to find other thermodynamic properties.

2. The changes in properties like T,p and v
a) depend on the path taken
b) are independent of path
c) depends on the property to be evaluated
d) none of the mentioned

Explanation: The changes in these properties depend only on the end states.

3. When does an equation of state reduces to the ideal gas equation?
a) when the pressure approaches zero
b) when the temperature approaches infinity
c) both of the mentioned
d) none of the mentioned

Explanation: This can be seen clearly in a generalized compressibility factor chart.
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4. When does the compressibility factor take the value 1?
a) for an ideal gas
b) when pressure approaches zero
c) when temperature approaches infinity
d) all of the mentioned

Explanation: We have lim(pv/RT) = 1 when p tends to zero and when T tends to infinity.

5. Which of the following statement is true?
a) for equation of state, the critical isotherm should have a point of inflection at the critical point
b) the isochore of an equation of state on a p-T diagram should be straight
c) both of the mentioned
d) none of the mentioned

Explanation: (∂p/∂v)=0 and (∂p/∂T)=constant.

6. On a Z-p compressibility factor chart as p approaches zero, at the Boyle temperature the slope of the isotherm is
a) zero
b) unity
c) negative
d) positive

Explanation: (∂z/∂p) = 0 at Boyle temperature.

7. On a Z-p compressibility factor chart as p approaches zero, the slope of the isotherm should be ____ at lower temperatures and ____ at higher temperatures.
a) positive, negative
b) negative, positive
c) negative, negative
d) positive, positive

Explanation: These are trends seen on a Z-p compressibility factor chart.

8. For the inversion curve, Joule-Kelvin coefficient is unity.
a) true
b) false

Explanation: the value of Joule-Kelvin coefficient is zero.

9. According to the equation of state, the Boyle temperature is
a) 2.56*Tc
b) 2.50*Tc
c) 2.52*Tc
d) 2.54*Tc

Explanation: Here Tc is the critical temperature.

10. An isotherm of maximum slope on Z-p plot as p approaches zero is called the foldback isotherm and its value is
a) 10*Tc
b) 2*Tc
c) 5*Tc
d) 2.54*Tc

Explanation: Here Tc is the critical temperature and this value is correct for many gases.

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