Chemistry 1 Homework Question

[agentb159]

If anyone here knows some chem. i was wondering if I could get some help with this problem.

It has to deal with how much heat is produced from the reaction

"When 1.34g of potassium bromide dissolve in 74g of water in a styrofoam cup calorimeter, the tempature drops from 18 degrees C to 17.279 degrees C. Assume all the heat is abosorb in the solution process comes from the water."
A. write a balanced equation for the solution prcess.
B. is this reaction endothermic or exothermic (I got this one as endothermic)
C. what does heat equal in joules when 1.34g of KBr dissolve ( I also got this one as 227.06j)
D. what does heat equal in Kj when 1 mole of Kbr dissovles.

I figured out b, and c but can't seem to get a, or d. Any help is appreciated.

Thanks Alex

[zskillz]

a) KBr(s) + H20(l) -> Br-(aq) + K+(aq) + H20(l)
i'm pretty sure that's it.. don't know if you need water in there even, but you prof might like to see it.

B) endothermic since heat is absorbed by the water

c)i believe that your supposed to use the [delta]q=mc[delta]T equation for this one... maybe.. dang, i cant' remember for sure
you will need to check all the units for c, b/c i can't remember them and probably need to use kelvin as well

to solve D, you simply need to spend a bit of time doing unit conversions of essentially the same calculation that you did in c.


hope that helps
-Z

[agentb159]

OK for B I used H (which stands for heat or can be Q). The formula was H=m*C(specific heat)*Delta T(change in temp.) but my questions for this is do i have to use the specific heat of water or the specific heat of water plus the Potassium bromide?

And if the answer I got for C is correct then I figured out D correctly also.

Thanks

Alex

[zskillz]

well, ideally, you'd use the specific heat of the solvent (which is h20+kbr), but in this case, i would be that you're just supposed to be using the specific heat of water.

ask you TA or your teacher

-Z