Question

How is it that ice-cream appears cooler to the mouth than water at $0{}^\circ \text{C}$.

Answer 1

Ice-cream absorbs the heat energy from our mouth to convert from solid to liquid state. Hence, ice-cream melts in our mouth.

Complete step by step answer:
Solid changes into liquid by absorbing heat. This process is called melting. When we have an ice-cream, the ice-cream melts in our mouths. To change from the solid to the liquid state, the ice-cream absorbs heat from our mouth. Thus, making it cool. Also, when liquid changes to solid, it loses its latent heat of fusion. The ice-cream even though at the same temperature as water appears cooler to the mouth because it has less heat energy as compared to water. Water on the other hand has its latent heat of fusion. It will only lose its latent heat when it becomes solid.
Additional information:
1 g of ice at $0{}^\circ \text{C}$ requires 334 J of energy to melt. This is called latent heat of melting. Subsequently, 334 J of energy is released by water when it freezes. This is called the latent heat of fusion.For a substance to change its state, it absorbs or releases some energy which is called the latent heat.

Note: Water at $0{}^\circ \text{C}$ also cools the mouth as it absorbs heat from the mouth. This transfer of heat occurs due to difference in temperature. But it does not appear as cool as ice-cream because ice-cream absorbs a greater amount of energy from the mouth when changing its state from solid to liquid.