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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: upsidedown on May 29, 2008, 04:38:23 PM

Title: Cracking equations
Post by: upsidedown on May 29, 2008, 04:38:23 PM

I know when cracking usually an alkane and an alkene is produced, but why when cracking hexane the equation

C6H14 → C3H6 + C3H8

and not C6H14 → C4H8 + C2H6

because both are an alkane and an alkene.

Thanks for any help

Title: Re: Cracking equations
Post by: cliverlong on May 29, 2008, 04:47:12 PM

Quote from: upsidedown on May 29, 2008, 04:38:23 PM

I know when cracking usually an alkane and an alkene is produced,

Agreed

Quote

but why when cracking hexane the equation

C6H14 → C3H6 + C3H8

and not C6H14 → C4H8 + C2+H6

because both are an alkane and an alkene.

Is "C2" an alkane or alkene ?

Is "H6"  an alkane or alkene ?

But separately, I have read that cracking produces a "variety" of hydrocarbon (emphasis intended) products . So going back to your first equation

C₆H₁₄ → C₃H₆ + C₃H₈

I'm not sure that C₃H₆ + C₃H₈ will be the only products - which is where you came in.

Now ... going back to what you wrote I guess you made a slight slip and meant

C₆H₁₄ → C₄H₈ + C₂H₆

which balances OK.

However, it might be the case that the energy of the various paths favour the production of certain products rather than others, or that there might be "rules" that guide where the splitting takes places - but I haven't come across them.

I too will be interested to find out if there is a "definitive" answer to this.

Clive

Title: Re: Cracking equations
Post by: upsidedown on May 29, 2008, 04:50:29 PM

Sorry the C2+H6 is a typing mistake, I have corrected it now.