Exam help

1. Nov 3, 2005

sarahisme

Hi all, i am currently studying for an exam, and so i am going over the questions in last years exam. Unfortunately we were not given the answers, so i am not sure whether i am getting the questions right.
If its not too much trouble, and someone has a bit of time to spare, could they verify the answers to some of the questions i put up?

Thanks
Sarah

my first question is this:

(a) 0.063kg of ice melt
(b) 4 moles
(c) 14940 J
(d) 83.1 J/K

Last edited: Nov 3, 2005
2. Nov 3, 2005

verty

Chemistry is not my thing. I get a different answer for the first one but I don't know if my method is right. Perhaps you see something in it though.

I figured that 0.5kg of 600K lead has 38.4kJ of heat. The freezing of the lead removes 12.4kJ or so, which leaves 26kJ. Melting ice requires 334.5kJ/kg, so that gives me 0.078kg. Take from it what you will.

3. Nov 3, 2005

sarahisme

this isnt meant to be chemistry, lol, it is a physics course, though i spose this is a very 'chemistry' part of it.

yeah i think my answer for (a) might be wrong.

how did you come up with :
"I figured that 0.5kg of 600K lead has 38.4kJ of heat"

i guess you did it by using q = mc(delta T)

where delta T = 600 K

so we use absolute zero then, hmm interesting! :)

your method makes a lot of sense :D

Last edited: Nov 3, 2005
4. Nov 3, 2005

Chi Meson

(a) I get 99 g
(b) correct
(c) righto
(d) yes.

5. Nov 3, 2005

sarahisme

cool, how did you get your 99g?

oh and how are you guys on relativity? :P

6. Nov 3, 2005

verty

Look at the units of 0.128 kJ/(kg.K), to get kJ out of that you multiply by kg and K. 0.5kg * 600K * 0.128 = ?

7. Nov 3, 2005

sarahisme

ok, yep i see that , cheers :)

8. Nov 3, 2005

sarahisme

would it be cool if i asked some relativity questions aswell?

9. Nov 4, 2005

Chi Meson

Sure, but start a new thread. If it is just a general question on SR, you should ask it in the SR forum. IF it is homework help you need, then ask it here.

edit: P.S. Special relativity and General Relativity is a sub-forum under "Astronomy and Cosmology"

10. Nov 4, 2005

k. thanks :)