Understanding Energy Differences in Ice and Water at 0°C

Let's explore why particles in liquid water at 0°C possess more energy compared to particles in ice at the same temperature, 0°C. This phenomenon is related to phase changes and the concept of latent heat.

Phase Change from Ice to Liquid Water

When ice melts into liquid water at 0°C, it undergoes a phase change from solid to liquid. This process requires energy to break the bonds holding the water molecules in the rigid structure of ice. Even though the temperature remains constant at 0°C during melting, energy is being absorbed by the ice.

The Role of Latent Heat of Fusion

The energy absorbed during the melting process, without causing a change in temperature, is known as the latent heat of fusion. This energy is used to increase the potential energy of the water molecules, allowing them to move more freely and overcome the strong intermolecular forces present in the solid state.

• In ice at 0°C, the particles (water molecules) are held in a fixed lattice structure by strong intermolecular forces. Their energy is primarily vibrational.
• During melting, heat energy is absorbed by these particles.
• This absorbed energy increases the potential energy of the particles, allowing them to break free from the fixed lattice structure.
• The particles then gain translational and rotational motion, characteristic of the liquid state.
• Liquid water at 0°C therefore has higher internal energy (specifically, higher potential energy) than ice at 0°C, even though the temperature (related to average kinetic energy) is the same.

Analyzing the Options

Let's examine the given options based on this understanding:

1. the particles in water absorb heat energy during the process of conversion from ice to water vapour: This describes sublimation or vaporization, not the direct conversion from ice to liquid water at 0°C.
2. Because the particles in ice absorb heat energy during the process of conversion from ice to liquid water: This statement accurately describes the process. The particles in the ice absorb the latent heat of fusion, which increases their energy content as they transition to the liquid state at the same temperature.
3. the particles in water radiate heat energy during the process of conversion from ice to liquid water: This is incorrect. Melting is an endothermic process, meaning it absorbs heat, not radiates it.
4. the particles in water absorb heat energy during the process of conversion from ice to liquid water: While water particles (once formed) are part of the system, the energy is absorbed by the substance undergoing the phase change, which initially is ice. Option 2 is a more precise description of where the energy absorption happens during the transformation from ice.

Thus, the reason particles in liquid water at 0°C have more energy is because the ice particles absorbed heat energy (latent heat of fusion) to transform into liquid water at that temperature.

Revision Table: States of Matter and Energy

Additional Information: Internal Energy and Latent Heat

The internal energy of a substance is the total energy possessed by its particles, including kinetic energy (related to temperature) and potential energy (related to the forces between particles and their arrangement). During a phase change like melting, the temperature remains constant, meaning the average kinetic energy of the particles doesn't change. However, the absorbed latent heat increases the potential energy of the particles by enabling them to overcome intermolecular forces and change their arrangement. Therefore, the total internal energy of the substance increases during melting, explaining why liquid water at 0°C has more energy than ice at 0°C.

The specific latent heat of fusion of ice is approximately \(334 \text{ kJ/kg}\). This means \(334 \text{ kJ}\) of energy is absorbed by \(1 \text{ kg}\) of ice at 0°C to turn into \(1 \text{ kg}\) of water at 0°C.