The Student Room Group

Can specific heat capacity be negative?

I had a question in which said temperature went from -18 to 0 degrees Celsius. As far as I know the difference in temperature between those numbers is -18, which got me a negative number
Your temperature difference should be the finishing temperature minus the starting temperature, which is 18.
Reply 2
I missed out this question **** sake.
Original post by Dusky Mauve
Your temperature difference should be the finishing temperature minus the starting temperature, which is 18.


So -> -18-0 but is still -18
Original post by Rxha
So -> -18-0 but is still -18


0-(-18) = 18
Original post by S2M
I missed out this question **** sake.


did you not see it or had no time?
Original post by Dusky Mauve
0-(-18) = 18

Ugh I screw up then! ,never knew you could switch around the numbers cuz I thought since the difference of the numbers is -18. Thanks
Reply 7
Original post by Rxha
did you not see it or had no time?


No time, no ****ing clock in the exam room.
Original post by S2M
No time, no ****ing clock in the exam room.


No clock ?! Wow I thought it was mandatory lol next time bring a watch and place it on top of the table to check time
Original post by Rxha
I had a question in which said temperature went from -18 to 0 degrees Celsius. As far as I know the difference in temperature between those numbers is -18, which got me a negative number


you're doing your subtraction the wrong way around a-b isn't the same as b-a

for SHC questions you'll be looking for the change in temperature from an initial temperature to a final temperature... the number of degrees that is added to (or subtracted from) the initial temperature Θinitial to get to the final temperature Θfinal
.
Θinitial+ΔΘ=Θfinal

so what you need to do is Θfinalinitial

e.g. if a sample went from 20 to 25 degrees the ΔΘ would be 25 - 20 = 5 degrees


or in your case it's 0- -18
and because double negative makes a positive that = +18

----
Or alternatively convert all temperatures from Celsius to Kelvin and you'll always be working with positive numbers
Original post by Rxha
Ugh I screw up then! ,never knew you could switch around the numbers cuz I thought since the difference of the numbers is -18. Thanks


It should always be final minus initial as that is the 'difference'. Specific heat capacity can never be negative because it's an absolute property of the material :smile:

No problem
Reply 11
Original post by Rxha
No clock ?! Wow I thought it was mandatory lol next time bring a watch and place it on top of the table to check time


Yeah. I thought it was too. I missed out a few questions but I think I got C/B hopefully a B. Think I got an A on ISA so I'm going to try and get an A* on paper to to make it an A overall.
Original post by Joinedup
you're doing your subtraction the wrong way around a-b isn't the same as b-a

for SHC questions you'll be looking for the change in temperature from an initial temperature to a final temperature... the number of degrees that is added to (or subtracted from) the initial temperature Θinitial to get to the final temperature Θfinal
.
Θinitial+ΔΘ=Θfinal

so what you need to do is Θfinalinitial

e.g. if a sample went from 20 to 25 degrees the ΔΘ would be 25 - 20 = 5 degrees


or in your case it's 0- -18
and because double negative makes a positive that = +18

----
Or alternatively convert all temperatures from Celsius to Kelvin and you'll always be working with positive numbers

Oh okay now I get it , oh well atleast I know I got 3 out of 4 ,
When you are finding a difference you always take the smallest number from the biggest, So it is always positive. You cant have negative energy? Since its a scalar
Original post by LorryBalls
When you are finding a difference you always take the smallest number from the biggest, So it is always positive. You cant have negative energy? Since its a scalar


You could have been taking heat out of something, i.e. cooling it. that would give you negative ΔΘ
It shouldn't be negative unless you're cooling something. But even then, the question would ask for "energy lost" so it would expect a positive nubmer.

Always check if your answer is reasonable. In this case, you should be expecting something positive. Use your common sense - if it seems unlikely, check it by working backwards. But don't get too hung up over it (I've done that before) - sometimes unlikely-sounding answers turn out to be correct.

Quick Reply

Latest