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Topic: Bond dissociation enthalpy  (Read 3750 times)

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Offline Rutherford

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Bond dissociation enthalpy
« on: June 03, 2012, 10:06:28 AM »
Found on the IChO, and it seemed very interesting to me:
Calculate the Si–Si bond dissociation enthalpy of Si2H6 from the following informations:
Bond dissociation enthalpy for H–H = 436 kJ/mol
Bond dissociation enthalpy for Si–H = 304 kJ/mol
ΔfH [Si(g)] = 450 kJ/mol
ΔfH [Si2H6(g)] = 80.3 kJ/mol

2Si(g)+3H-H(g) :rarrow: H3Si-SiH3(g)
I have two expresions to calculate ΔH:
ΔH=ΔfH [Si2H6(g)] - 2ΔfH [Si(g)]
ΔH=3Bond dissociation enthalpy(H-H) - 6Bond dissociation enthalpy(Si-H) - Bond dissociation enthalpy(Si-Si)
And I got that the bond dissociation enthalpy(Si-Si)=303.7kJ/mol, but I found somewhere on the net that Si-Si=around 50. Did I calculate this wrong or not?

Offline Schrödinger

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Re: Bond dissociation enthalpy
« Reply #1 on: June 04, 2012, 12:46:24 AM »
50 is most probably in kcal/mol units.
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Offline Rutherford

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Re: Bond dissociation enthalpy
« Reply #2 on: June 04, 2012, 08:12:46 AM »
Is my calculation right?

Offline AWK

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Re: Bond dissociation enthalpy
« Reply #3 on: June 05, 2012, 04:44:04 AM »
Robin Walsh
Acc. Chem. Res. 1981,14, 246-252
(Table 4)   74 kcal/mol= 309 kJ/mol
AWK

Offline Schrödinger

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Re: Bond dissociation enthalpy
« Reply #4 on: June 05, 2012, 05:25:43 AM »
I worked it out got the same result. I think we're right. Calculation seems legit to me
"Destiny is not a matter of chance; but a matter of choice. It is not a thing to be waited for; it is a thing to be achieved."
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Offline Rutherford

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Re: Bond dissociation enthalpy
« Reply #5 on: June 05, 2012, 08:03:46 AM »
Ok, thanks.

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