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Thermochem prob.

iCrazzy · 2015-12-06 19:28:15

Taken from the 2012 q6 chem paper. My teacher did it out for us but never properly explained it. I get everything apart from the given line part. Why do you include o2? And where does 25 over 2 come from. Really would appreciate any help.

06-12-2015 08:28PM

#1

iCrazzy

Registered Users, Registered Users 2 Posts: 204 ✭✭

Join Date: August 2013

Posts: 148

Taken from the 2012 q6 chem paper.
My teacher did it out for us but never properly explained it.
I get everything apart from the given line part.
Why do you include o2? And where does 25 over 2 come from.

Really would appreciate any help.

0

Comments

#2 09-12-2015 09:34PM

Sleee

Registered Users, Registered Users 2 Posts: 1 ✭

Join Date: December 2015

Posts: 1

Hey! The O2 is included as heat of combustion is the heat change when one mole of a substance is burned in excess oxygen. thus in heat of combustion equations oxygen is always included.

As for the 25 over 2, to balance the equation C8H18 + 25/2O2
> 8CO2 + 9H2O. At the end, there are 25 oxygens on both sides as the 2's cancel in 25/2o2 and there is 2(8)=16 oxygens in 8co2 and 9 oxygens in 9h2o. kinda hard to explain with just words but that's the explanation.

0