Ice at 273 K (0°C) is more effective in cooling than water at the same temperature because ice absorbs extra heat from the surroundings in the form of latent heat of fusion when it melts. This latent heat is the energy required to change ice from solid to liquid at constant temperature without increasing the temperature of the ice itself. Water at 273 K, being already in liquid form, cannot absorb this additional latent heat; it can only absorb heat to raise its temperature. Therefore, ice at 273 K takes in more heat overall from the surroundings, causing a stronger cooling effect than water at the same temperature.
Key Points
- Ice melts at 273 K by absorbing latent heat of fusion (about 334 J/g) from the surroundings without changing temperature.
- Water at 273 K absorbs only sensible heat to increase its temperature; it does not undergo a phase change.
- The latent heat absorbed by ice results in a greater loss of heat from the surroundings, hence more effective cooling.
- After melting, ice (now water) can also absorb sensible heat, further increasing total heat absorbed.
In summary, the phase change of ice consumes substantial heat energy making ice at 273 K more effective in cooling than water at the same temperature.
