Midterm Question

$\Delta U=q+w$

Hailey Johnson
Posts: 31
Joined: Wed Nov 16, 2016 3:04 am

Midterm Question

In question 3 on the midterm, when calculating the heat required to change the temperature of the pot and the water, why do we use degrees Celsius and not Kelvin? Does it matter which one I use in future problems?

Joshua Hughes 1L
Posts: 81
Joined: Sat Jul 22, 2017 3:01 am
Been upvoted: 3 times

Re: Midterm Question

for this problem, it really shouldn't matter so long as you use a specific heat that has Kelvin in the units so they can cancel out properly. The only time you really should worry about converting to Kelvin is when it is in the natural log of T2/T1. make sure T2 and T1 Kelvin in those cases I think

Jessica Patzlaff 1A
Posts: 28
Joined: Fri Sep 29, 2017 7:05 am

Re: Midterm Question

For that specific problem it was ok to use Celsius because we were calculating the change in temperature, so it would be the same regardless of if it was in Celsius or Kelvin.

Rachel Wang
Posts: 49
Joined: Fri Sep 29, 2017 7:04 am

Re: Midterm Question

In this question they provided heat capacity constants in both J.K-1.mol-1 and J.C-1.g-1. You'll have to pay attention to which temperature the use based on which heat capacity constant you use. Personally I find it very helpful to write down the units as you are solving instead of only incorporating units at the end.
Commonly, an instance in which you'll need K is when you use Gas constant R = 8.314 J.K-1.mol-1.

Pooja Nair 1C
Posts: 55
Joined: Thu Jul 13, 2017 3:00 am

Re: Midterm Question

Because you are calculating a change in temperature, a change in celsius is the same as a change in kelvin. Be sure to convert the units if you aren't doing a change in temp calculation, because most of the constants deal with Kelvin, or if the question specifically asks you to report temperature in a specific unit