IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: ayesha. on May 28, 2010, 02:46:51 pm

Title: Chemistry enthalpy question
Post by: ayesha. on May 28, 2010, 02:46:51 pm

Calculate the standard enthalpy change for the following rxn.

CH4 + 2O2(g) ? CO2(g) + 2H2O(l)

?Hf CO2 = -394 KJ/mol
?Hf H2O = -286KJ/mol
?Hf CH4 = -75 KJ/mol

Using the standard enthalpy of formation of methane and the data given below calculate the mean bond enthalpy of C-H bond in methane.

C(s) ? C(g) ?Hat of graphite = +715 KJ/mol
H2(g) ? 2H(g) ?H= +436 KJ/mol


Using the C-H bond enthalpy calculated and the standard enthalpy change for the reaction given below, calculate the mean bond enthalpy of the C-C bond in propane

C3H8 (g) ? 3C(g) + 8H(g)

Title: Re: Chemistry enthalpy question
Post by: ayesha. on May 28, 2010, 02:48:56 pm

enthalpy change for the last rxn is +4020 KJ/mol

Title: Re: Chemistry enthalpy question
Post by: nid404 on May 28, 2010, 02:55:23 pm

What's the "?"  ?

Title: Re: Chemistry enthalpy question
Post by: ayesha. on May 28, 2010, 08:59:16 pm

delta

Title: Re: Chemistry enthalpy question
Post by: unknown 101 on May 28, 2010, 09:03:54 pm

which pastpaper is this question from??
cuz if its not from a past paper then upload it here, cuz ur confusing everybody!!

Title: Re: Chemistry enthalpy question
Post by: ayesha. on May 29, 2010, 08:31:41 am

its not a pastpaer question
nvm i got the answer