[charlie20]

Hi

Im trying to work out the temperature rise that would result if the following chemical reaction occurred;
2Fe²⁺+3H₂O₂->2Fe³⁺+2OH^-+2H₂O+O₂
But to do so i need the specific heat capacity of the Fe and OH ions, and i cant find this anywhere! Does it not exist?! Is there another way to calculate the temp. rise from the EQ without using H=cpT?
Thanks
Charlie

[hmx9123]

Presumably you're not doing this in the gas phase?  There are specific heats for solutions of ions, although IIRC, they can be a little more complicated because they depend on concentration, etc.  Maybe at someplace in your book/lab manual it says to assume that the Cp is that of water (which is pretty big)?  That would simplify things tremendously.  Other things to take into account are the heat of solution of oxygen, which will be dissolving in the water as it escapes the solution, and any evaporative cooling due to gas loss, although those are both very small in comparison to the heat of reaction.

[charlie20]

Hi
Sorry i should of made clear that this is not a book problem. Im trying to build a simple thermochemical model of the above reaction, to find the temperature rise that would occur with the reaction.
Im am doing some chemistry tests on the catalytic breakdown of hydrogen peroxide. I have found that iron (II) chloride when added to hydrogen peroxide, catalysises decomposoition. Both the FeCl2 and the H2O2 are aqueous solutions.
I believe the above reaction occurs, with the oxidation of the Fe ions from the Fe(II), to Fe (III). I am sure the above reaction is what occurs, but do not understand what happens to the Cl- ions. Does anyone have a clue?!
Also could you point me towards a book where i could find the specific heat capacity of the ions? I have tried the CRC Handbook, to no avail.
Perhaps i could rewrite the above equation so that everything is in solution; how would i do this?

Cheers for any help
Charlie

[xiankai]

a catalyst is one that remains chemically unchanged.

the Fe2+ ions remain as they are, at the end of the reaction.

this is because the peroxide first oxidises the Fe2+ to Fe3+, then additional peroxide reduces the Fe3+ back to Fe2+ with the help of the H+ formed from the first reaction.

[charlie20]

Thanks for your reply Xankai - interesting!

I think i should of called the iron (II) Chloride a "catalyst" rather than a true catalyst. I do believe the iron changes valence state.
Your statement;
"this is because the peroxide first oxidises the Fe2+ to Fe3+, then additional peroxide reduces the Fe3+ back to Fe2+ with the help of the H+ formed from the first reaction. "
interests me, but the reason why i say that the Fe2+ goes to Fe3+ is from a colouration point of view. Initially the iron (II) chloride, in aqueous solution, is green, then when added to the colourless peroxide solution it turns brown, with oxygen being evolved. this colour change agrees with the oxidation of Fe(II) to Fe(III). The solution does not change back to green, even when left for a while.

what do you mean "with the help of the H+ formed from the first reaction. "?  How is this H+ formed?

Thanks for any help that anyone can give!
Charlie

[xiankai]

i just searched abit more, and i realise this may not be the path that the decomposition of H2O2, since based on wikipedia,

http://en.wikipedia.org/wiki/H2O2#Decomposition

"In the presence of certain catalysts, such as Fe2+ or Ti3+, the decomposition may take a different path, with free radicals such as HO· (hydroxyl) and HOO· being formed."

im not very sure what exactly happens, but this is obiviously not a basic decomposition like i outlined earlier  

as for your last question, "what do you mean "with the help of the H+ formed from the first reaction. "?  How is this H+ formed?"

i think i have made a mistake, the H+ is required to oxidise the Fe2+ because hydrogen peroxide reacts different under acidic or basic mediums. rather, OH- is needed.

http://en.wikipedia.org/wiki/H2O2#Redox_reactions

my apologies for any confusion i may have caused, its been a long time since i've touched a chemistry book