When ice is melting, we know that the temperature stays constant at 0 ℃. If we were to place ice at 0 ℃ in a sufficient amount of water at ambient temperature, would the temperature of the water itself also stay constant during the time the ice is melting, or is it only the temperature of the ice that stays constant? Does the actual cooling of the water occur after or during phase change?
No, as the ice is melting, the water is cooling down. Ice melts in water because the water molecules in solution collide with those in the ice, giving them energy. In exchange, the water molecules in solution slow down a little during the collision. While the Ice does not change temperature as it is melting, the energy from the water is going into breaking the crystal structure of the ice, turning it into water. This process consumes energy, and the energy to fuel this process comes from the water in solution. Another factor to consider is conservation of energy - if energy is being put into breaking the ice, where else could that energy come from but from the water?