JEE Physics 2025 Question with Solution

Given: Ice is melting at $273 \, \text{K}$ and atmospheric pressure.

Find: Which statement is correct during melting.

During melting, ice changes phase to water at constant temperature. The important physical fact here is that the volume decreases because water is denser than ice.

So the surroundings compress the system slightly, which means positive work is done on the ice-water system by the atmosphere.

Using the first law of thermodynamics,

where $\delta W$ is work done by the system.

Since heat is absorbed during melting, $\delta Q > 0$. Because volume decreases, work done by the system is negative, so work is effectively done on the system.

Therefore, the statement 'Positive work is done on the ice-water system by the atmosphere' is correct. The correct option is D.

Given: Melting of ice at $273 \, \text{K}$ under atmospheric pressure.

Find: The correct thermodynamic statement.

Melting is an isothermal phase change, but that does not mean internal energy remains unchanged. Heat is absorbed as latent heat of fusion.

Also, during melting of ice, volume decreases slightly. Therefore,

At atmospheric pressure, work done by the system is

Hence,

So the atmosphere does positive work on the system.

From the first law in the form used in the solution,

Here $\Delta Q > 0$ and $\Delta W > 0$ when interpreted as work done on the system. Thus internal energy increases, so options A and C are incorrect.

Hence, the correct option is D.