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Which of the following change is observe...

Which of the following change is observed occurs when a substance X is converted from liquid to vapour phase at the standard boiling point?
I. Potential energy of the system cecreases
II. The distance between molecules increases
III.The average kinetic energy of the molecules in both phases are equal

A

I only

B

II only

C

III only

D

II and III only

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question regarding the changes observed when a substance X is converted from liquid to vapor phase at the standard boiling point, we will analyze each statement provided. ### Step-by-Step Solution: 1. **Understanding the Phase Change**: - When a substance transitions from liquid to vapor, it undergoes a phase change known as vaporization or boiling. This occurs at the standard boiling point of the substance. 2. **Analyzing Statement I**: - **Statement I**: "Potential energy of the system decreases." - During the phase change from liquid to vapor, energy is supplied to the liquid. This energy is used to overcome the intermolecular forces holding the liquid molecules together. As a result, the potential energy of the system actually **increases** because energy is stored as potential energy in the form of intermolecular separation. Thus, this statement is **false**. 3. **Analyzing Statement II**: - **Statement II**: "The distance between molecules increases." - In the liquid phase, molecules are closely packed due to intermolecular forces. When the substance transitions to the vapor phase, these forces are overcome, and the molecules move further apart. Therefore, the distance between the molecules **increases** during this phase change. This statement is **true**. 4. **Analyzing Statement III**: - **Statement III**: "The average kinetic energy of the molecules in both phases are equal." - The average kinetic energy of gas molecules is given by the equation \( KE = \frac{3}{2}RT \), where R is the gas constant and T is the temperature. At the boiling point, the temperature remains constant during the phase change. Since the temperature is the same for both the liquid and vapor phases at the boiling point, the average kinetic energy of the molecules in both phases is indeed **equal**. Thus, this statement is **true**. 5. **Conclusion**: - Based on the analysis: - Statement I is false. - Statement II is true. - Statement III is true. - Therefore, the correct option is **2 and 3 only**. ### Final Answer: The correct answer is **2 and 3 only**.
To solve the question regarding the changes observed when a substance X is converted from liquid to vapor phase at the standard boiling point, we will analyze each statement provided. ### Step-by-Step Solution: 1. **Understanding the Phase Change**: - When a substance transitions from liquid to vapor, it undergoes a phase change known as vaporization or boiling. This occurs at the standard boiling point of the substance. 2. **Analyzing Statement I**: ...
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Knowledge Check

  • A liquid is in equilibrium with its vapour at its boiling point. On the average, the molecules in the two phases have equal: 1)potential energy 2)total energy 3)kinetic energy 4)intermolecular forces.

    A
    potential energy
    B
    total energy
    C
    kinetic energy
    D
    intermolecular forces.

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