Posted by Bob on .
At a restaurant, your glass of water contains 25% ice while your friend’s glass of water contains 75% ice. What can you say about their temperatures? Explain your answer
In both cases the temperatures will be close to 0°C.
Whenever you have water and ice in thermal equilibrium, the temperature will be 0°C. When you put a big piece of ice in water at room temperature, then the ice will at first melt fast, but this costs a lot of heat, and the water cools down rapidly. The water-ice system quicly reaches a steady state situation very near to thermal equilibrium.
The water will be very close to 0°C, but just a bit warmer than that, especially near the edge of the glass it will be a bit warmer. Near the ice it will be colder, only slightly above 0°C. The ice itself will be 0°C at the surface, the interior of the ice will be slightly below 0°C.
Then you know that heat flows from high temperature to low temperatures. So, these small temperature differences cause heat flow from the surrounding air into the glass of water and rom there into the ice which slowly causes the ice to melt.