# Homework Help: Total heat removed from phase change

1. Feb 7, 2010

### clickyclicky

Ethyl alcohol has a boiling point of 78.0°C, a freezing point of -114°C, a heat of vaporization of 879 kJ/kg, a heat of fusion of 109 kJ/kg, and specific heat of 2.43 kJ/(kg · K). How much energy must be removed from 0.584 kg of ethyl alcohol that is initially a gas at 78.0°C so that it becomes a solid at -144°C?

I know start out by finding the heat removed at the phase change.

Q1 = Lvm
= 879(0.584)
= 513.336 kJ

Then the heat involved to cool the liquid to −114°C...

Q2 = cmΔT
= 2.43(0.584)(78− - 114)
= 272.471 kJ

Then the phase change at −114°C...

Q3 = Lfm
= 109(0.584)
= 63.656 kJ

Adding them all together to get the total heat...

Q1 + Q2 + Q3 = 513.336 + 272.471 + 63.656 = 849.463 kJ

But webassign won't take my answer. What did I do wrong?

Edit: I figured out what I did wrong. Didn't pay attention to the final temperature. Got it right this time. :)

Last edited: Feb 7, 2010
2. Dec 9, 2014

### Alyaa

Hi, not sure if you'll be able to see this since this thread was posted 4 years ago but what did you mean by u didn't pay attention to the final temperature? What did you do right?