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Homework question 8.41

Posted: Wed Jan 24, 2018 8:09 pm
by Michelle Chernyak 1J
Hi, I'm struggling with the set up for this question (8.41). I thought I knew how to do it, ( I set -q_ice=q_water) but my answer is off by a little bit. Can anyone help out please?

Re: Homework question 8.41

Posted: Wed Jan 24, 2018 9:06 pm
by Shawn Patel 1I
Hey,
You're on the right track. Heat gained by the ice cube is heat lost in the surrounding water. For the ice cube, you have to consider the enthalpy of fusion of the ice, meaning you have to calculate the amount of heat it takes to melt the ice, and then add it to the amount of heat that is gained as the temperature rises. Then solve for the final temperature.

Re: Homework question 8.41

Posted: Wed Jan 24, 2018 10:46 pm
by Caitlin Mispagel 1D
Also, remember that enthalpy of fusion is given in Kj per mole so you have to multiply by the number of moles you are working with. Another problem I encountered was units. Enthalpy of fusion uses kJ while specific heat uses J so make sure to account for that!

Re: Homework question 8.41

Posted: Fri Jan 26, 2018 8:05 pm
by Evelyn L 1H
It would actually be q_ice= -q_water because the heat used to melt the ice comes from the water so water is losing the energy that the ice gains.

Re: Homework question 8.41

Posted: Fri Jan 26, 2018 8:07 pm
by Evelyn L 1H
Sorry, I just realized that which side the negative sign is on doesn't matter too much because it will end up canceling out and giving you the same answer, but it helps to think of it conceptually and visualize what is actually physically happening.