JEE Main 2025 · 3 April · evening · Single correct · +4 / −1
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
- (a) Both Statement I and Statement II are false
- (b) Statement I is true but Statement II is false
- (c) Both Statement I and Statement II are true
- (d) Statement I is false but Statement II is true
Answer and solution
Answer (c) Both Statement I and Statement II are true
Solution
Chemistry ma’am · 3 steps
While ice melts, the heat goes into breaking hydrogen bonds, not into speeding molecules up.
- Statement I. Ice and water in equilibrium sit at the melting point, 0 °C at 1 atm. Heat supplied now melts more ice instead of warming the mixture. The temperature stays fixed until the last bit of ice is gone. True.
q = n Δ_(fus)H (at constant T)
- Statement II. Temperature measures the average kinetic energy of the molecules. At the melting point the absorbed heat (the latent heat of fusion) is used to overcome the attractions between water molecules in the ice lattice, mainly hydrogen bonds. It raises their potential energy, not their kinetic energy. True.
- So. Both statements are true, and Statement II gives the reason behind Statement I. The answer is (c).
The idea to keep. During any phase change at its transition temperature, heat goes into potential energy (breaking intermolecular attractions). Kinetic energy, and so temperature, stays constant.
Answer from the NTA final answer key. Solution by PrepWiser.