[echo.fritch]

An 9.5 ice cube is placed into 275 of water. Calculate the temperature change in the water upon the complete melting of the ice. Hint: Determine how much heat is absorbed by the melting ice and then use to calculate the temperature change of the 275 of water. I have NO idea. I tried doing it like it asked and I was wrong. Help?

[echo.fritch]

By the way, that's 9.5 GRAM ice cube in 275 GRAMS of water. But I just would like to know how to solve it. I couldn't find anything in the chapter on how to do it :(

[DrBob1]

The procedure must be in your book. You need to know the heat of fusion of ice and the specific heat of water. The heat gained by the ice and its 9.5 grams of melt water equals the heat lost by the starting 275 grams of water as it cools. Besides not specifing the weight of the water and ice, you must also give the starting temperatures of both the ice and the water. Try it. We will be glad to provide any further help you need.

[echo.fritch]

The starting temperatures were not given. Sooo..

[DrBob1]

You really must have the starting temperatures. I thought maybe you can calculate the CHANGE in temperature regardless of the actual temperature, but you can't. It is like trying to get the average of two unknown numbers - just can't be done. I think you will have to wing it for your homework (that sounds like what this is). Assume the ice is at 0 oC and the water is at room temperature: 25 oC.Post back if you are shown a way to do the problem, I'd like to see it.

[jcaron2]

As DrBob already alluded, there are three different things that would happen here before an equilibrium temperature was reached. (1) First, the ice will heat up from its original temperature to 0°C. (2) At that point, it melts, thereby giving up its heat of fusion. (3) After that, the resultant 0°C water from the melted ice exchanges heat with the rest of the water in the glass until their temperatures are the same.

In reality, of course, the second and third steps occur at the same time. However, given that the question asks for the temperature drop at the exact instant that the last of the ice melts (NOT when the final equilibrium temperature is reached), I'd say the author is very stupidly making the assumption that the three steps occur one after the other. That also explains why the initial water temperature wasn't given.

So that means for this problem you only need to find the temperature change after the first TWO steps. However, the stupid author (have I mentioned what I think of this author?) also failed to give you the initial temperature of the ice. Therefore, like DrBob, I think you're supposed to assume its initial temperature is 0°C.

That means your problem really just comes down to step 2! Just calculate the heat of fusion of 9.5g of ice. Since the ice needed to "steal" that heat from the surrounding water in order to melt, the temperature of the 275g of water will have lowered by an equivalent amount.

<soapbox> Ambiguous questions like this one are unfortunately FAR too common in modern textbooks! It seems to me that in an effort to generate lucrative new releases of their books every year or two, publishers and authors have sacrificed quality and clarity. The point of an introductory physics or chemistry class is to teach students about physics or chemistry; it's not to assess their abilities to read the author's mind by having to interpret vague and ambiguous questions. All questions like this do is convince students that chemistry and physicals are mysterious and difficult and that they should try to avoid such subjects if possible!</soapbox>

Good luck!

[DrBob1]

On rereading the question, I think you are completely correct. Well thought out! (Unlike the question. It really is a bad question, both in wording and concept.)