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Enthalpy Of Combustion ( Calculation ) Guide Needed

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iAdoreNaz Male
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  #11 Old 05-10-2011 Default Re: Enthalpy Of Combustion ( Calculation ) Guide Needed

I have another question , but it's regarding enthalpy of formation and atomisation.
How can I change the title of this thread to "Enthalpy ( Calculation ) Q&A"?

By the way, here's the question.

1. Calculate the mean bond enthalpy of the SiF bond in SiF4(g) given :
enthalpy of formation of SiF4(g) = -1615kJmol-1
enthalpy of atomisation of silicion = +456kJmol-1
enthalpy of atomisation of fluorine = +79 kJmol1

The answer is : +597kJmol-1
What is the eaning of mean bond enthalpy ?
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  #12 Old 06-10-2011 Default Re: Enthalpy Of Combustion ( Calculation ) Guide Needed

just want to say thank you for the calculation and the corections.
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lxy Female
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  #13 Old 07-10-2011 Default Re: Enthalpy Of Combustion ( Calculation ) Guide Needed

Quote:
Originally Posted by iAdoreNaz View Post
I have another question , but it's regarding enthalpy of formation and atomisation.
How can I change the title of this thread to "Enthalpy ( Calculation ) Q&A"?

By the way, here's the question.

1. Calculate the mean bond enthalpy of the SiF bond in SiF4(g) given :
enthalpy of formation of SiF4(g) = -1615kJmol-1
enthalpy of atomisation of silicion = +456kJmol-1
enthalpy of atomisation of fluorine = +79 kJmol1

The answer is : +597kJmol-1
What is the eaning of mean bond enthalpy ?

Bond enthalpy is the enthalpy change when a bond in a gaseous molecule is broken.
Mean bond enthalpy is the average value of the enthalpy of one kind of bond in many different organic compounds, since the actual value of one particular bond will vary in different compounds/environments. I don't think there's a textbook definition for mean bond enthalpy.


SiF4 (g) -> Si (g) + 4F (g)

Si (s) + F2 (g)

Arrows from SiF4 (g) to lower eqn, from lower eqn to Si (g) and 4F (g)

Enthalpy for breaking of all four bonds = +1615 + 456 + 4(79) = 2387

Since you want the mean bond enthalpy of the SiF bond, divide that by four, round it off to 3 significant figures and you get 597.
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