Support NeoGAF

[Ronald_mcd]

The complete combustion of octane, a component of gasoline, is
represented by the equation:
2 C8H18(l) + 25 O2(g) 16 CO2(g) + 18 H2O(l)
How many liters of CO2(g), measured at 63.1 C and 688 mmHg, are
produced for every gallon of octane burned? (1 gal = 3.785 L; density of
C8H18(l) = 0.703 g/mL)


anyone know how to do this?

The choice of answers are


a. 7.48 L
b. 7.11 102 L
c. 5.68 103 L
d. 5.68 L
e. 1.07 103 L

 

[BlackSalad]

funny, we just did something similar in class today, I think it goes something like...


(1 L Octane) * (703g Octane / 1 L octane) * (1 mol Octane / 114.22g Octane) * (18 mol CO2 / 2 mol Octane) = mol of CO2

Then we use the ideal gas forumla V = (nRT/P)

688 torr == .902 atm
63.1 C == 336.25 K
so you can just plug in and find out the volume of CO2 produced by 1 L of octane, then multiply by 3.785 L / gal

I didn't actually do the problem but I think that's how it is done

 

[Dilbert]

funny, we just did something similar in class today, I think it goes something like...


(1 L Octane) * (703g Octane / 1 L octane) * (1 mol Octane / 114.22g Octane) * (18 mol CO2 / 2 mol Octane) = mol of CO2

Then we use the ideal gas forumla V = (nRT/P)

688 torr == .902 atm
63.1 C == 336.25 K
so you can just plug in and find out the volume of CO2 produced by 1 L of octane, then multiply by 3.785 L / gal

I didn't actually do the problem but I think that's how it is done

The procedure would go something like this:

1) Figure out how many moles are in one gallon of gasoline. This calculation will involve molar weight (g/mol) and density.

2) Use the mole ratio in the equation to figure out how many moles of CO2 are created from the available moles of octane. (Multiply by 8 since it's a 2:16 ratio.)

3) Convert moles to liters using the ideal gas law.

I'm pretty sure the stuff he just said is right, but my coffee hasn't kicked in yet, and I can't read what he just wrote with a clear understanding. (Jet lag sucks.)

 

[Ronald_mcd]

The procedure would go something like this:

1) Figure out how many moles are in one gallon of gasoline. This calculation will involve molar weight (g/mol) and density.

2) Use the mole ratio in the equation to figure out how many moles of CO2 are created from the available moles of octane. (Multiply by 8 since it's a 2:16 ratio.)

3) Convert moles to liters using the ideal gas law.

I'm pretty sure the stuff he just said is right, but my coffee hasn't kicked in yet, and I can't read what he just wrote with a clear understanding. (Jet lag sucks.)

Thats it. Thanks guys

 

[Overseer]

I had Chem 1 last year. I didn't have the courage to move on to Chem 2 though.

 

[Loki]

Always good to get to these topics late and save myself the finger work.


What Black Salad said above is correct as far as I can tell; hopefully you're ok with dimensional analysis (conversion of units and equivalence of units as derived from the balanced equation etc., as seen in Black Salad's post)-- it's actually one of the biggest time savers in physical chemistry problems, and it also helps you avoid a lot of confusion with units.


EDIT:

I had Chem 1 last year. I didn't have the courage to move on to Chem 2 though.

If you did well in chem 1, don't let chem 2 intimidate you. In my opinion, the only somewhat challenging part of the course was buffer solutions (and the factors that affect them); chem 1 is more qualitative for the most part, whereas chem 2 is more qualitative (problems take a lot longer due to the numbers involved). Chem 2 does introduce a lot of important concepts, however, most notably Gibbs free energy and voltaic cells/batteries (easiest topic in the course imo, but also very relevant to the "real world", and interesting). Most of the other stuff is an elaboration on the basic concepts introduced in chem 1. Give it a shot.

 

[Draff]

Hm who's your prof? Rashmi?
I'm not sure who first year chem profs are this year.

Or maybe Teitelbaum

Looks like WebCT assignments.

Organic > Inorganic