Gas Stoichiometry Question

[man0005]

Consider the combustion of biogas, in excess oxygen, in an engine designed to generate electricity. If the combustion is 100% efficient, CH4 is the only constituent of the biohas and the only products are CO2 and H2O.
a) What volume of gas products will be formed at 927 degrees and 110kPa if 25 kg of CH4 is burnt?
b) If the gas products are then cooled to STP, what volume will they now occupy?>

a) I think water is a gas product, so i got
v ( CO2) = 141,716
v (H2O) = 283,432

b) v ( CO2) = 35,009.3
v (H2O) = 76,430.5

Any help/corrections would be greatly appreciated

[m@tty]

At that temp, H2O is definitely a gas.





And from the reaction CH4 : products = 1:3

So,

(3 sf)

Cooled to STP, T=273K, p=101.3 kPa. Work by ratio:

(3sf)

[simonhu81292]

i got something different ...
but it's very similar to yours..~~
my answers are:
a)
CO2= 141,647L
H2O=283,295L
b)
CO2= 34,992L
H2O=69,984L
 

[simonhu81292]

25000/16= 6250..haha
1562.5..that's what i've got

[m@tty]

Oh lol. I shall rectify that

[man0005]

oh matty
doesnt the pressure change to STP conditions as well when its cooled or is it just the temp?

[m@tty]

Yes, yes it does. How foolish I am. =\

[man0005]

oh okay
how come our answers for water in b) are so different simon O_O

[m@tty]

Mine and simons numbers now agree after I corrected the pressure in b)..

[simonhu81292]

yeah ..i know ...i was surprised as well..
but i double checked ...
let's wait for someone else for confirmation

thanks matty~~!

[man0005]

ah i used R = 8.31 instead of R = 8.314 for a)
and got 141648 L for CO2
think that must be it
does it matter much?

[m@tty]

I only used 8.31?

Not that it matters now, but always use the values given in the data book for the exam (obviously). We also used it for SACs at my school.. Friendly advice from a moderator (atone for my terrible attempt at answering your question haha)

[man0005]

oh okay
yeah I used 8.314 thats why it was different I think
i think i'll leave it since i've used 8.314 for everything else. hopefully teacher isnt too mean considering this is the first piece of hw

if you guys have some time, i have one more quick question
A certain pharmaceutical company produces a medication that contains 40.0 mg of magnesium hydroxide, Mg(OH)2, per ml. This is the only consitituent of the preparation with acid-base properties.

Calculate the concentration of hydroxide ions in the mixture
i got 1.37 M

[m@tty]

In one litre there will be 40g of magnesium hydroxide.

(this is the same as the concentration in M as it is the mol in a litre)

So (3sf) So you're correct.

EDIT: I like my post-count - it was 4040 :coolsmiley:

[man0005]

om goshh, thanks heaps
do you have any time atm to help me with a few physics questions?