q=mc∆t vs q=c∆t? (chapter 8)

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Zoe Robertson 2H
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Joined: Fri Jun 17, 2016 11:28 am

q=mc∆t vs q=c∆t? (chapter 8)

Postby Zoe Robertson 2H » Mon Mar 13, 2017 5:54 pm

Hi! Could anyone clarify when to use q=mc∆t vs q=c∆t? I was working on question 8.53 and I was going to use q=mc∆t but the 'm' wasn't included in the solution. Thank you!!

Jessica Huang 1M
Posts: 26
Joined: Wed Sep 21, 2016 2:59 pm

Re: q=mc∆t vs q=c∆t? (chapter 8)

Postby Jessica Huang 1M » Mon Mar 13, 2017 6:44 pm

The C given in the problem is in units of kJ/C.

You want your q to be in units of Joules or kJ.

If you used the q=mC(delta T) with your given C, your q would be in units of (grams)(kJ).

In the problem, you were given the heat capacity, not the specific heat capacity. Therefore, you don't need mass to calculate q.

Laura Rabichow 1J
Posts: 29
Joined: Fri Jun 17, 2016 11:28 am

Re: q=mc∆t vs q=c∆t? (chapter 8)

Postby Laura Rabichow 1J » Mon Mar 13, 2017 9:52 pm

In general, you can figure it out based on the units of the given C. You typically want q to be in kJ or J. Like Jessica said, in your example problem the C was given in kJ/˚C, so you would only multiply by the temperature. If your C was given in kJ/(˚C*mol), you would use q = nC∆T. If your C was given in kJ/(˚C*g), you would use q = mC∆T. Also, don't forget to convert moles of substance to grams or vice versa if it doesn't match the C given!

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