Why there is no change in temperature when freezing and melting of ice into water?

Answer 1

When you add the heat of fusion (also called enthalpy of fusion) to ice at zero degrees centigrade, the energy involved serves to change the form of the material from ice to water, and it does not increase temperature. See link.

Answer 2

"Ice is a solid, which means that the bonds between the water molecules in ice are much stronger than in liquid water. Now as long as there is still ice in your mixture, the energy you add as you heat will be used up to break these strong bonds....."

Wrong! Weaker chemical bonds are broken first before stronger ones. (Duh.) But that is not the reason why the temperature of melting ice does not rise. When you apply heat to ice, its temperature actually rises until it reaches melting point where it begins to--guess what--melts. And melts. And melts. At the melting point. Which is a constant. Which is why the T of melting ice does not rise.

Looking at it thermodynamically, let's say you apply heat on top of an ice block. The heat causes the top layer to reach melting point, so it melts. The liquid water carries the heat away from the block. The farther it goes, the faster its temperature will rise due to ambient heat. You can even make a graph of water temperature as a function of distance from the ice block. The area closest to the block will have the lowest temperature. (But of course.)

But let's say your block is in a small confined space. This means the liquid water does not have enough space to go. Instead of the ambient heat driving up the temperature of this liquid water, the heat from this water is quickly transferred TO the newly formed liquid water coming from the block (and vice versa), forming an equilibrium temperature.

To make this clearer, let's say the ice suddenly stops melting altogether. What will happen to the already liquid water? Its temperature will RISE due to heat transfer FROM the ambient heat (until it reaches equilibrium). If the ice begins to melt again, the heat exchanges will make sure the temperature will NOT rise from the equilibrium point. Until of course, the ice melts completely.

Answer 3

The ice temperature does not change because it is still ice. If its' temperature rises above 32 degree F, it becomes liquid. And the temperature of the liquid has risen above the freezing point.