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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Tensdale on March 25, 2012, 06:25:23 AM

Title: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: Tensdale on March 25, 2012, 06:25:23 AM: I have to calculate the balanced formula for gasoline; C8H18 (I know it's a extremely simplified formula) when it has been burned.

And I'm completely lost here. I have no idea how to calculate how much O is needed to calculate the difference between a complete and uncomplete combustion.
Do I just chose a number or?

EDIT: Okay, so I've sort of figured out how many O molecules I need.
I need 16 O to make CO2 out of the 8 carbon. And I need 9 O to make H2O out of the 18 H. So 25 in all. How do I write this? Because I'm pretty sure I need dioxygen. But I can't really write C8H18 + 12,5 O2.
And C8H18 + 25O, looks.... Off.
Title: Re: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: Borek on March 25, 2012, 06:56:08 AM: 12.5O₂ is OK - at least during balancing. Final step is to change coefficients so that they become the smallest possible integers. In this case just multiply everything by 2, yielding 2C₈H₁₈ + 25O₂...
Title: Re: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: Tensdale on March 25, 2012, 06:57:21 AM: Ah, yes. That's what I forgot.

THANK YOU ;D

EDIT: Oh, wait. Before I forget, why exactly is it that I need dioxygen? Why will it not work with just 25O?
Title: Re: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: Borek on March 25, 2012, 07:05:17 AM: Oxygen (as several other gases - N₂, halogens) is present at STP as diatomic molecules.
Title: Re: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: Tensdale on March 25, 2012, 07:11:41 AM: And what does that mean in english?
(I'm being teached in another language, so if you don't spell it out for me, I have have no idea what you're talking about)
Title: Re: How do I know how many oxygen molecules are needed in a redox reaction?
Post by: XGen on March 25, 2012, 11:45:26 AM: Instead of existing as singular O atoms, they exist as O₂ where the oxygen forms a double bond with another oxygen. This is how it occurs naturally.