(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

80g of ice initially at zero degrees C is allowed to melt in 200g of water initially at 20 degrees C.

Find the energy change of the water, energy change of ice

Find entropy change in water, ice, and universe.

2. Relevant equations

Delta S = Q/T

Q = (Specific heat)(mass)(Delta T)

Lf = heat of fusion

Cw = specific heat of water (yes I know it's 4.184ish J/grams degrees C, but he doesn't like us using numbers).

3. The attempt at a solution

My physics instructor spent a half-hour defining entropy in about 18 different unique-to-him ways, and an hour and a half on random tangents that didn't really have much to do with entropy or even physics. No equations were given, no problems were demonstrated.

So I'm just going to attempt to solve this using methods I remember from high school chemistry about fifteen years ago, and I'm hoping maybe someone can tell me if I'm way off my rocker.

so Qice = (80)(Lf) + (80)(Cw)(Tf-0)

and Qwater = (200)(Cw)(Tf-20)

Since I know energy from the water is going into the ice:

(80)(Lf) + (80)(Cw)(Tf-0) = -(200)(Cw)(Tf-20)

Since the final temperature is the only real variable there, I can solve for that and come up with values for the Qs.

As far as entropy goes though, this isn't a constant temperature process. In the equation Delta S = Q/T, if indeed that is the equation I should be using, do I put the final temperature there below the Q change required to reach it? Would the entropy change of the universe be the sum of those two Delta Ss?

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# Homework Help: Entropy Problems

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