Can you solve this?

General Forums Off-topic Chat
#1

Hey, I was wondering if anyone here could solve this chemistry problem, because I got pretty far on it, but now I’m stuck. %|

Anyway, it’s for extra credit, and my chemistry professor said I could use ANY source… :slight_smile:

Okay, here it is:
A cylinder contains 3.00 g of liquid octane(C8H18 and an initial O2 pressure of 1.00 atm. The cylinder is fitted with a piston and initially occupies a volume of 10.00 L at 298 Kelvin. The octane is completely consumed by the reaction. Approximate that the piston is massless and frictionless and that the cylinder neither absorbs or releases heat. Calculate the final volume occupied by the cylinder.

Okay, so I am just assuming that this is an ideal gas, using PV=nRT and such, and I’ve already figured out the initial and final states of the stuff. Here it is:
Initial Volume: 10.00 L
Initial Pressure: 1 atm
Initial Temp: 298 K
Initial # of mols of gas: 0.409 mol

The balanced reaction: C8H18(liquid) + 25/2O2(gas) --> 8CO2(gas) + 9H2O(gas)

Final number of mols of stuff:
O2: 0.0802
CO2: 0.2104
H2O: 0.2367

I can’t seem to figure out how to get the final heat, though…

Anyway, If you think you can solve it, please, try! :smiley:

#2

This is a great idea! Utilizing the extensive Blenderhead knowledge pool to get help with your schoolassignments :slight_smile: Sorry, can’t help you though, Lemmy. Hrm, by the way, you wouldn’t happen to have read Steven Pinker’s "The language instinct, would you? :wink:

#3

Enthapy of combustion of octane is 48.23 kJ/g

So for three grams it is thrice this.

Molar specific heat capacity at constant pressure of an ideal gas is (5/2)kT where k is Boltzmann’s constant.

Integral of energy in over heat capacity w.r.t. temp from T old to T new gives equation. Rearrange to get T new.

Pretty sure that should work, but it is late and I am tired.

Alex

#4

My brain hurts :expressionless:

#5

yay chemistry… wait… oh dang I forgot most of my chemistry… wow in only 6 month!
Anyway being more helpful. I might not remember my chemistry well (not to speack of my physics) but I do remember basic algebra. no I’m pretty sure what I did is probably a mistake… it must be a mistake since it was easy. I just calculated R and used you final data to caculate V. now, from what I remember in this kind of reactions (exothermic) temperature change… and because there are more gas at the end pressure must change… but I really couldn’t remember any formula to calculate this so I just didn’t changed it. assuming this is where youre problem than - good luck. if not and thos thingies are constant that… v=12.8913L. must you remember I didn’t done anything related to chemistry for about 6 month so I don’t really sertify as a big help.

#6

That’s a good book…
most interesting…

#7

Okay, I turned in the assignment, so I’ll await the grade. :slight_smile:

alicopey158: thanks so much. I was doing it wrong before. Thank you. :smiley:
And thanks to everyone else who tried to help. :slight_smile: