Question:
Consider the phase diagram of a one component system. Va, Vb and Vliquid are the molar volumes of alpha, beta and liquid phases respectively. Which one of the following statements is true?
\begin{center}
\includegraphics[width=0.7\textwidth]{05.jpeg}
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Given: The change in molar enthalpies, DeltaH alpha to beta and DeltaH beta to liquid, are positive.
Consider the phase diagram of a one component system. Va, Vb and Vliquid are the molar volumes of alpha, beta and liquid phases respectively. Which one of the following statements is true?
\begin{center} \includegraphics[width=0.7\textwidth]{05.jpeg} \end{center} Given: The change in molar enthalpies, DeltaH alpha to beta and DeltaH beta to liquid, are positive.
\begin{center} \includegraphics[width=0.7\textwidth]{05.jpeg} \end{center} Given: The change in molar enthalpies, DeltaH alpha to beta and DeltaH beta to liquid, are positive.
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Whenever enthalpy change is positive, the transition is endothermic and entropy increases. In phase transitions solid to solid to liquid, the molar volume generally increases in the same order.
Updated On: Aug 23, 2025
- Va < Vb and Vb < Vliquid
- Va > Vb and Vb < Vliquid
- Va < Vb and Vb > Vliquid
- Va > Vb and Vb > Vliquid
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The Correct Option is A
Solution and Explanation
Step 1: Interpretation of given data
The diagram shows the transitions alpha to beta to liquid. Since DeltaH alpha to beta and DeltaH beta to liquid are positive, both transitions are endothermic, which means entropy increases during each transition. Step 2: General principle
For a single component system, when entropy increases, disorder increases. This usually also leads to an increase in molar volume. Step 3: Ordering of volumes
Alpha is the most compact solid phase, Beta is a less compact solid phase, and the liquid phase has the largest molar volume. Therefore, the order is: Va < Vb < Vliquid. Step 4: Checking the options
Option (A): Va < Vb and Vb < Vliquid is correct. Option (B): Va > Vb is incorrect. Option (C): Vb > Vliquid is incorrect. Option (D): Va > Vb and Vb > Vliquid is incorrect. \[ \boxed{\text{Correct relation is Va < Vb < Vliquid}} \] %Quicktip
The diagram shows the transitions alpha to beta to liquid. Since DeltaH alpha to beta and DeltaH beta to liquid are positive, both transitions are endothermic, which means entropy increases during each transition. Step 2: General principle
For a single component system, when entropy increases, disorder increases. This usually also leads to an increase in molar volume. Step 3: Ordering of volumes
Alpha is the most compact solid phase, Beta is a less compact solid phase, and the liquid phase has the largest molar volume. Therefore, the order is: Va < Vb < Vliquid. Step 4: Checking the options
Option (A): Va < Vb and Vb < Vliquid is correct. Option (B): Va > Vb is incorrect. Option (C): Vb > Vliquid is incorrect. Option (D): Va > Vb and Vb > Vliquid is incorrect. \[ \boxed{\text{Correct relation is Va < Vb < Vliquid}} \] %Quicktip
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