If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)

Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

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 7:28pm

#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 8:34pm

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