[Isomer]

Here is the info I was given..

Mass of Al Calorimeter......470.0 grams
Mass of Calorimeter Water.....100.0 grams
Initial Temp of Calorimeter Water.....23.0 degrees Cel
Mass of Silicon......52.0 grams
Initial Temp of Silicon......61.6 degress Cel
Final Temp of Calorimeter, Water, and Silicon....24.6 degress Cel

The amount of energy lost by silicon in the experiment is ...

a. 670 Joules
b.1.35 KJoules
c. 2.25 KJoules
d. 3.82 KJoules


I keep getting D, but the answer is B. The formula I use is q=mc^t water +  mc^t aluminium.

Then I just plug in numbers and 3.82. What the heck am I doing wrong???

[Yggdrasil]

I plugged in the numbers and got (B), so something must be wrong with your calculations.  What numbers are you using for the specific heats (c) of water and aluminum?  By the number you got out of the calculation, it looks like you may be using the same specific heat for both materials.  Remember that specific heat is a property of a certain material and changes for different materials, so the specific heat of water is different than the specific heat of aluminum.  The specific heat of water is about 4.183 J g^-1 K^-1 and the specific heat of aluminum is about 0.900 J g^-1 K^-1 (source: http://en.wikipedia.org/wiki/Specific_heat_capacity).  Try using these numbers and see what answer you get.

[Isomer]

Thanks. I think I got it now.