posted by Matt .
Your hot tub has overheated to a very uncomfortable 48 degrees C. If your hot tub contains 402 L of hot water, what mass of ice at -5 degrees C would you need to add to your hot tub to bring the temperature down to a more comfortable 36 degrees C?
You have to heat the ice to 0
you have to heat to melt the ice at0c
then you have to heat the melted ice to 36C
then you have to "heat" (negative heat) the original water from 48 to 36
the sume of all these heats is zero.