7 replies to this topic

[Amir_Tambe]

Hi i am a second year student. I am stuck at s point where i need to find the heat of reaction. I have decided to calculate it like (del H) of reaction = sum of (del H) formation of products - sum of (del H) formation of reactants. But i am not able to find the formation heat of either the reactant or the product.( i hv searched perry, smith vanness etc). i have now decided to calculate the heat of formation from bond enthalpies. i hope have taken a right decision? if not please correct me. hpw do i go about calculating it. can someone help me out. it will be of great help. Thanking you in anticipation.

[JEBradley]

The best way to arrive at the enthalpy of reaction is by experimental measurement.
ΔH_Products - ΔH_Reactants is fine but make sure you state the assumption that factors such as enthalpies of solution or enthalpies of mixing are negligible (they usually are) - 'Crystallisation' by Mullins is a good source of data for this.

You said you couldnt find ΔH_f for the product but you also stated that the product was unknown - this would explain why you couldn't find it

Can you tell us what the reaction is then we might be able to tell you what the enthalpies of formation are from our own resources. Have you tried consulting the CRC Handbook of Chemistry and Physics?? That tends to be a good resource.

If all other sources are truly exhausted then yes use bond energies - although as molecules increase in complexity, your figure will lose its accuracy.

[hoyoku]

I'm having the same problem in my final year design project. You could look for this book "Properties of fluids and liquids" or the "Internation Critical Tables". Hope this helps!

Joseph

[Padmakar Katre]

Dear,
You can try with a book named Chemical And Physical Properties Handbook By Yaws where you will find the regression coeff to find out the diff properties.And the formula as you stated is not unique its only applicable to the endothermic reactions and in case of the exothermic reactions the heat content of the reactants is more than the products.Any how this book is quite useful as I referred it for my graduation project when internet facilities to have online calculations were not that familier.

Regards,
Padmakar Katre

[JEBradley]

The equation will apply for both exothermic and endothermic reactions. It may be negative for exothermic but this only signifies that heat moves out of the chemical system (+ve being arbitrarily taken as heat movement in).

What is meant by regression coefficient to find out diff properties (differential or different??)

[Padmakar Katre]

Dear JEBradly,

My humble request to you to go through this book and you will come to know how the different properties are calculated at the different pressure and temperature with the help of these regression coefficients.I hope you will do it for me .Hummmmm..........

Regards,
Padmakar Katre

[Amir_Tambe]

I have consulted m professor regarding this and he suggested me to refer to 'Properties of gases and liquids' by Reid Sherwood and Prauznitz. Unfortunately none of these books which you people mentioned are available in my college library. Neither did i find the book of Reid and Sherwood which my professor suggested. Actually i am not involved in any project or something like that. I am just trying to explore things which would widen my knowledge.
The reaction scheme which was given to me is something like this:
C6H4(SO3Na)2 + 4NaOH = C6H4(ONa)2 + 2Na2SO3 + 2H2O
I found this scheme when i was searching the net for Resorcinol. I was studying Heat of reaction as it was in my syllabus and consequently decided to explore my skills. And the rest of the story is known to you people.
The problem now i am facing is that i am not even aquainted with the concept of " bond energies".
Can you suggest me some books where i can try my luck out.?
Thanking you for your cooperation and i am extremely sorry that i was away for so many days.

[engware]

Hi there:

Here are two plots on the HHV and physical properties.




I would suggest to check out the following web site for physical properties:
http://www.nist.gov

Thanks,

Gordan