Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: anujfr on November 29, 2012, 06:04:05 PM
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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.
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Any related equations that you know?
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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.
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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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ΔH has the unit KJ
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ΔH has the unit KJ
I am absolutely sure that's incorrect.
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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.
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Why is the mass given in the question?
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6.55 g of C6H5NH2
But why does the mass matter considering that heat capacity doesn't involve mass???
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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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Well logic says no, given that the substance burnt in both scenarios is the same. But why do you ask???
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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.
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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.
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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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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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What's the MW of C6H5NH2? You will need it.
If ΔHrxn=qrxn and q= C*ΔT, then C =j/°c and q=j. Then doesn't ΔH = j instead of J/moles?
You are confusing people by using non standard notation. Joules ≡ J and never j.
Even better practice is to always define your notation.
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The K is actually a lower case k but I don't think that is the confusion.
It may not be the confusion in this case, yet get into the habit of doing notation right. Notation is important.
Kilo- (symbol: k, lowercase)
Always kJ and never KJ
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What is the "right" answer?
The right answer is 6.84 kJ/°C
What's the MW of C6H5NH2? You will need it.
What is MW??
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Molecular Weight, or Molar Weight.
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Sorry but I am confused. Do you want the Molecular mass * 9.8 or just the mass. I am confused because you said weight which is mass * acceleration due to gravity.
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Sorry but I am confused. Do you want the Molecular mass * 9.8 or just the mass. I am confused because you said weight which is mass * acceleration due to gravity.
Why don't you think about it a bit? Have you seem Molecular Mass * 9.8 being used in a ThermoChem Context?
Even better if you are so wracked by doubt report both. My point is let's start doing some number crunching.