[anujfr]

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-> ΔH_rxn = -1.28 * 10^4.

Thank You.

[Borek]

Any related equations that you know?

[anujfr]

ΔH_rxn=q_rxn.
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.

[Borek]

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.

ΔH_rxn = -1.28 * 10^4

Units?

[anujfr]

ΔH has the unit KJ

[Borek]

ΔH has the unit KJ

I am absolutely sure that's incorrect.

[anujfr]

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.

[Borek]

Why is the mass given in the question?

[anujfr]

6.55 g of C₆H₅NH₂

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

[Borek]

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?

[anujfr]

Well logic says no, given that the substance burnt in both scenarios is the same. But why do you ask???

[fledarmus]

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.

[anujfr]

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 ΔH_rxn=q_rxn 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.

[Borek]

If ΔH_rxn=q_rxn 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?

[curiouscat]

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?