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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: sandiegofan328 on September 30, 2018, 07:51:44 PM

Title: Thermochem question...
Post by: sandiegofan328 on September 30, 2018, 07:51:44 PM

Hello all,
I'm having quite a bit of trouble finding the answer to this Thermochemistry question, it is not located in either our textbook or lecture...I apologize for not showing my beginning work as I just lack direction on where to begin. I appreciate all attempts or hints to get me started. :)

4 Fe(s) + 3 O2(g)  2 Fe2O3(s)      ΔH = -1652 kJ
How much heat is released when 12.8 g Fe and 1.66 g O2 are reacted?

Would I convert to moles, multiply by the coefficient, and then multiply by delta H?
Thank you much

Title: Re: Thermochem question...
Post by: sjb on October 01, 2018, 02:27:29 AM

Check your units, but almost there

Title: Re: Thermochem question...
Post by: Borek on October 01, 2018, 02:43:21 AM

Deciding what is the limiting reagent won't hurt, but yes, as sjb suggested, you are on the right track.

Title: Re: Thermochem question...
Post by: aSad on October 01, 2018, 03:54:24 PM

hi, this is my first message on this forum...
is the given enthalpy for 1 mol of product?
if it is so, you should find the limiting reactant and with it, find the amount of Fe₂O₃.
then, multiply the mol number with the enthalpy, the result is the heat released...

Title: Re: Thermochem question...
Post by: Borek on October 01, 2018, 04:05:48 PM

Quote from: aSad on October 01, 2018, 03:54:24 PM

is the given enthalpy for 1 mol of product?

If it is not listed as per mole in most cases it is meant for a "reaction as written", so my bet would be 2 moles.

Title: Re: Thermochem question...
Post by: Enthalpy on October 01, 2018, 06:37:07 PM

Yes, 2 moles of Fe₂O₃. The Hdbk of Chem & Phys gives -824.2kJ/mol.

Title: Re: Thermochem question...
Post by: sandiegofan328 on October 02, 2018, 09:09:22 AM

Thanks for your help everyone, I plugged it in as 1 mole per the delta H and it worked.