Question

A schematic Pressure-Temperature diagram of water is shown in the figure. Which of the following option(s) is/are correct?

 

• A. Clausius-Clapeyron equation is valid across the melting curve and the vaporization curve
• B. Melting curve has the highest slope
• C. The critical point exists only for the vaporization curve
• D. Clausius-Clapeyron equation is not valid across the melting curve and the vaporization curve

Hint:

The Clausius-Clapeyron equation is used to relate the pressure and temperature of a substance during phase changes. It is valid across both the vaporization and melting curves, and the melting curve often has a steeper slope compared to the vaporization curve, especially in the case of water.

Answer 1

The Correct Option is A, B, C

Step 1: Validity of the Clausius-Clapeyron Equation.
The Clausius-Clapeyron equation describes the relationship between pressure and temperature during phase transitions such as melting and vaporization. It is valid across both the melting curve (fusion curve) and the vaporization curve (evaporation curve), as these transitions involve latent heat and changes in phase. The equation is particularly useful for calculating the slope of these curves.

Step 2: Slope of the Melting Curve.
The melting curve corresponds to the equilibrium between the solid and liquid phases. The slope of this curve can be derived from the Clausius-Clapeyron equation, and it is indeed steep compared to the vaporization curve. In some cases, especially for water, the melting curve has a relatively higher slope compared to other phase transition curves.

Step 3: The Critical Point.
The critical point is the point at which the liquid and gas phases become indistinguishable. This point exists only for the vaporization curve (the liquid-gas transition) and does not exist along the melting curve (the solid-liquid transition).

Step 4: Correct Answer.
Option (A) is correct because the Clausius-Clapeyron equation is valid for both the melting curve and the vaporization curve.
Option (B) is correct because the melting curve often has the highest slope, especially for water, where the slope between the solid and liquid phases is steeper.
Option (C) is correct because the critical point exists only for the vaporization curve, marking the end of the liquid-gas phase boundary.
Option (D) is incorrect because the Clausius-Clapeyron equation is valid across both the melting and vaporization curves.

Thus, the correct answer is (A), (B), and (C).