# Thermodynamics Questions and Answers – P-T and T-S diagram for Pure Substance

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “P-T and T-S diagram for Pure Substance”.

1. Which of the following curves meet at triple point?
a) fusion curve and vaporization curve
b) fusion curve and sublimation curve
c) vaporization curve and sublimation curve
d) fusion curve and vaporization curve and sublimation curve

Explanation: At triple point, all these three curves meet.

2. The slopes of sublimation and vaporization curves for all substances are
a) negative
b) positive
c) zero
d) none of the mentioned

Explanation: This is true for all substances.

3. The slope of the fusion curve for water is
a) negative
b) positive
c) zero
d) none of the mentioned

Explanation: The slope of fusion curve for most substances is positive but for water it is negative.

4. The temperature at which a liquid boils is very sensitive to pressure but the temperature at which a solid melts is not such a strong function of pressure.
a) true
b) false

Explanation: The slope of the fusion curve is small.

5. Which of the following statement is true?
a) the triple point of water is 273.16 K
b) the triple point of CO2 is 216.55 K
c) when solid CO2 is exposed to 1atm pressure, it gets transformed into vapour directly
d) all of the mentioned

Explanation: The solid CO2 absorbs the latent heat of sublimation from the surroundings which gets cooled.
Sanfoundry Certification Contest of the Month is Live. 100+ Subjects. Participate Now!

6. The equation which forms the basis of the Mollier diagram is
a) Tds=-dh+vdp
b) Tds=dh+vdp
c) Tds=dh-vdp
d) none of the mentioned

Explanation: This equation form the basis of the h-s diagram of a pure substance also called the Mollier diagram.

7. Which of the following statements is true?
a) the slope of an isobar on h-s coordinates is equal to the absolute saturation temperature at that pressure
b) is the temperature remains constant, the slope will also remain constant
c) if the temperature increases, the slope of the isobar will also increase
d) all of the mentioned

Explanation: Here absolute saturation temperature is given by Tsat+273.

8. Which of the following represents the latent heat of vaporization at a particular pressure.
a) Hf-Hg
b) Hg-Hf
c) Hf+Hg
d) none of the mentioned

Explanation: Here Hg is the specific enthalpy of the saturated vapour and Hf is the specific enthalpy of the saturated water.

9. At critical pressure, value of Hg-Hf is
a) two
b) one
c) zero
d) infinity

Explanation: As pressure increases, there is a decrease in Hg-Hf and at critical pressure its value becomes zero.

10.In the Mollier diagram, the constant pressure lines diverge from one another.
a) true
b) false

Explanation: As the pressure increases, the saturation temperature also increases, increasing the slope of the isobar.

Sanfoundry Global Education & Learning Series – Thermodynamics.
To practice all areas of Thermodynamics, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]