# Homework Help: Stuck on this phase change question!

1. Mar 6, 2006

### dan greig

I have a question on dropping ice (-10 celsius) into water (20 celsius). What is the final temp?

i have used Q = m.c.delta T between -10 and 0

I know i have to use Q = m.l for the phase change and then agian use

Q = m.c. delta T to find a final temp.

How do i relate these two equations to each other to find the final temp?

2. Mar 6, 2006

### HallsofIvy

You didn't say how much ice or how much water. First calculate how much heat it would take to raise the temperature of the ice to 0 and how much heat it would take to melt the ice. Call the sum of those H1. If H1 is larger than the heat the water would lose in dropping to 0 celcius, H2, then not all the ice will melt and the final temperature will be 0 celcius.

If H2 is larger than H1, use m.c. delta T= H2-H1 to determine the temperature of the water after the ice has melted (but is still at 0 celcius). Of course the c you use for water will be different from that for ice and their masses will be different. Call that T1. Finally, use m(ice water)delta T= m(water)delta T to solve for the final temperature.