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Chemistry Question 53 – JEE-MAIN 2025

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Given below are two statements: Statement I : When a system containing ice in equilibrium with water (liquid) is heated, heat is absorbed by the system and there is no change in the temperature of the system until whole ice gets melted. Statement II : At melting point of ice, there is absorption of heat in order to overcome intermolecular forces of attraction within the molecules of water in ice and kinetic energy of molecules is not increased at melting point. In the light of the above statements, choose the correct answer from the options given below

During a phase transition (like melting or boiling), the temperature of a substance remains constant even as heat is absorbed or released.

Step 1: Analyze Statement I✦ Active

Statement I describes the phenomenon of latent heat of fusion. When a substance undergoes a phase change (e.g., ice melting into water) at its melting point, the absorbed heat energy is used to change the state rather than increasing the temperature. Therefore, the temperature remains constant until the entire phase change is complete. This statement is a fundamental principle of thermodynamics.

Step 2: Analyze Statement II○ Expand

Statement II provides the molecular explanation for the constant temperature during melting. The absorbed latent heat energy is utilized to overcome the intermolecular forces of attraction (specifically hydrogen bonds in ice) that hold the molecules in a rigid solid structure. Since the temperature does not increase, the average kinetic energy of the molecules, which is directly proportional to temperature, also does not increase at the melting point. This statement is also correct.

Step 3: Conclusion○ Expand

Both Statement I and Statement II accurately describe the process of melting of ice and the underlying molecular reasons. Therefore, both statements are true.

💡 Teacher's Secret Hint

Remember that temperature is a measure of average kinetic energy. If temperature is constant, kinetic energy is constant.

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