Question

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. Statement I is true but Statement II is false
• B. Statement I is false but Statement II is true
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Hint:

During a phase transition (like melting or boiling) at a constant pressure, the temperature of the system remains constant while heat is absorbed or released. This heat is known as latent heat and is used to overcome or establish intermolecular forces, rather than increasing the kinetic energy of the molecules.

Answer 1

The Correct Option is C

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. When ice and water are in equilibrium at the melting point (0°C at 1 atm), any heat added to the system is used to overcome the latent heat of fusion, which is the energy required to change the phase of ice from solid to liquid without increasing the temperature. The temperature of the ice-water mixture remains constant at the melting point until all the ice has melted. Therefore, Statement I is true. 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. Melting involves the transition from a more ordered solid phase (ice) to a less ordered liquid phase (water). To achieve this phase change, energy must be supplied to overcome the intermolecular forces of attraction (hydrogen bonds in ice) that hold the water molecules in a fixed lattice structure. The absorbed heat increases the potential energy of the molecules by increasing the distance between them, thus weakening the intermolecular forces. During the phase transition at the melting point, the absorbed heat does not increase the kinetic energy of the molecules; instead, it is used entirely to break the intermolecular bonds. Therefore, the temperature (which is related to the average kinetic energy of the molecules) remains constant during melting. Thus, Statement II is also true. Since both Statement I and Statement II are true, the correct answer is (3).