[shaggybill]

In my class, we have a problem where we are figuring out how much heat it takes to melt an ice cube. In the experiment, one of the steps is to take the ice out of the icemaker and place it into a beaker of water before putting it into a styrofoam cup later on in the experiment. One of the questions is: "why can't you use the ice directly out of the icemaker (why place it in water first), and if you did use it directly out of the icemaker, what would you have to add to the equation to find the delta H_fusion?

I've been looking for the answer, but so far I haven't come up with anything that even remotely makes sense.

Thanks

[enahs]

I am not really sure how well this method will work.

But ice can be less then 0^oC, and in fact, comes out of the freezer less then 0^oC.
Based on the third law of thermodynamics, you are assuming that if you put the ice in water, after a certain amount of time the ice and water should be at thermal equilibrium at 0^oC.

In a ideal simplified world, sure....but I am not sure how well that works in the real world.

[shaggybill]

Enahs, thanks for the reply. I should have given more details. The experiment is basically this:

1. Fill a beaker with a few ice cubes and add enough water to cover the ice cubes.

2. Next, take and weigh an empty styrofoam cup, then weigh it again after filling 2/3 up with hot water. Record these weights.

3. Measure temperature of the hot water with thermometer.

4. Take 5 ice cubes out of beaker, dry off with paper towel, add to cup of hot water.

5. Continue taking temp measurements at 30s intervals until ice cubes have melted.

6. Once ice has melted, record the weight of the cup/contents again.

Lastly, I use the recorded values in a long equation which yields  :delta:H_fusion.


The three questions are:

A) Calculate  :delta:H_fusion

B) Calculate % error

C) Why can't you use the ice directly out of the ice maker?

The first two questions are simple enough, but that third one is throwing me for a loop.

[macman104]

That is what enahs is saying.  :delta: H_fusion assumes that the ice is at 0°C.  When in reality, the ice is going to be below 0° when it comes out of the freezer.  So to account for that, you would need to use the specific heat of water to determine how much energy was used up just heating the ice to 0°C.

By leaving the ice in water for a little, you are making the assumption that before melting the ice, the water will first heat it to 0°C, and then you put it in the other water to perform the real test because now all the ice is at 0°C.

EDIT:  Also, to use the

Code: [Select]

:delta: you need to provide a space before you type the next character, otherwise it doesn't work (maybe I should post that in the forum section).

[shaggybill]

Oh, I see now. Great! You guys are awesome! Thanks so much.