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Topic: Find the heat capacity of the calorimeter.  (Read 4950 times)

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Offline anujfr

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Find the heat capacity of the calorimeter.
« on: November 29, 2012, 06:04:05 PM »
Please explain to me how can I find the answer to this question:

A 6.55 g of C6H5NH2 was combusted in a bomb calorimeter. The temperature change was 32.9 C. Determine the heat capacity of the calorimeter. Given-> ΔHrxn = -1.28 * 10^4.

Thank You.

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #1 on: November 29, 2012, 06:11:04 PM »
Any related equations that you know?
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Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #2 on: November 29, 2012, 06:16:01 PM »
ΔHrxn=qrxn.
That is all that I think is applicable for this reaction considering the amount of information I have.
Also
q=C*ΔT
But I am confused if I used this then would I find the C for the reaction or the calorimeter?

Because If the above equations are correct then I can assume C = ΔH/ΔT. which gives me a wrong answer.
« Last Edit: November 29, 2012, 06:31:35 PM by anujfr »

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #3 on: November 29, 2012, 06:39:56 PM »
Because If the above equations are correct then I can assume C = ΔH/ΔT. which gives me a wrong answer.

Generally speaking this is how it should be done.

ΔHrxn = -1.28 * 10^4

Units?
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Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #4 on: November 29, 2012, 06:41:38 PM »
ΔH has the unit KJ

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #5 on: November 29, 2012, 06:54:02 PM »
ΔH has the unit KJ

I am absolutely sure that's incorrect.
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Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #6 on: November 29, 2012, 06:57:43 PM »
The K is actually a lower case k but I don't think that is the confusion. It is Kilo Joules and I can scan and post the image of the page the question is on if you want.

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #7 on: November 29, 2012, 07:01:58 PM »
Why is the mass given in the question?
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Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #8 on: November 29, 2012, 07:06:22 PM »
6.55 g of C6H5NH2

But why does the mass matter considering that heat capacity doesn't involve mass???

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #9 on: November 29, 2012, 07:11:36 PM »
Say you burn 6.55 g of the substance. Say you burn 13.1 g of the substance. Is the amount of energy produced the same?
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Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #10 on: November 29, 2012, 07:30:57 PM »
Well logic says no, given that the substance burnt in both scenarios is the same. But why do you ask???

Offline fledarmus

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Re: Find the heat capacity of the calorimeter.
« Reply #11 on: November 29, 2012, 09:12:44 PM »
You're missing the point. ΔH does depend on the amount of the material reacting, and it's units should reflect that. All of Borek's responses have been trying to guide you to the missing piece.

Offline anujfr

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Re: Find the heat capacity of the calorimeter.
« Reply #12 on: November 29, 2012, 09:22:25 PM »
Oh I see what you are saying. I wonder why did my professor wrote kJ instead of kJ/moles...

But let me ask you this:
If ΔHrxn=qrxn and q= C*ΔT, then C =j/°c and q=j. Then doesn't ΔH = j instead of J/moles?

And we are talking about heat capacity intead of specific heat capacity.

Offline Borek

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Re: Find the heat capacity of the calorimeter.
« Reply #13 on: November 30, 2012, 04:25:45 AM »
If ΔHrxn=qrxn and q= C*ΔT, then C =j/°c and q=j. Then doesn't ΔH = j instead of J/moles?

No idea what is j.

How many joules were produced in combustion?
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Offline curiouscat

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Re: Find the heat capacity of the calorimeter.
« Reply #14 on: November 30, 2012, 06:17:09 AM »
Because If the above equations are correct then I can assume C = ΔH/ΔT. which gives me a wrong answer.

What is the "right" answer?

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