Question

Explain why the temperature of the water decreased when the cold water was added to the hot water.

Answer 1

Answer:

The water is clearly close to boiling temperature when you add the ice. And it would seem that you are are adding somewhat under 30% of ice to the hot water, and that he thermometer is near the bottom of the tank. So, initially the ice cools the water that is near it to near 0degC. Water between about 0 and 8 degrees is more dense than hotter water, so the cold water sinks to the bottom. The water is now circulating, so when the ice runs out the hotter water will be drawn fown from the surface for a while, causing rapid heating until the cooler water going up the other side of the tank slows things down. The plateau at the top probably represents some complexity in the mixing, after which you see a possible combination of effects, such as initial evaporation making the surface cool, and renewed convection. Evaporative cooling will of course slow quite rapidly, this will also slow the convection, so it is hard to tell what the final temperature (somewhat below room temperature) will be.

Hope it helps you