chemistry help?

Question

im stuck on this question:

Octane (C8H18) burns in oxygen to produce carbon dioxide gas and water vapour.
(i) Write a balanced chemical equation for this process.
(ii) Calculate the volume of carbon dioxide produced at 25 °C and a pressure of
1.01×105 Pa when 9.85 g of octane is used up in the combustion reaction.
(R = 8.314 J K-1 mol-1; Atomic masses: C = 12.01, H = 1.01, O = 15.99)

i got the balenced equation (C8H18----> 8CO2 +9H2O)
and the second part i was using the formula pV=nRT but it gives you grams of octane and asks for the volume of CO2...im totally confused. can anyone help me?

Answer 1

From equation 1 mole Octane produces 8 moles CO2

Therefore 114g Octane producles 352 CO2

So 9.85g Octane produces 9.85/114 x 352 g CO2

= 30.414 g CO2

Number of moles CO2 = Mass/ Mass in 1 mole

= 30.414/44 g CO2

= 0.691 moles CO2

V = (nRT)/P

V = (0.691x8.314x298)/1.01x10^5

V = 0.017 cm^3

Temperature has to be converted to kelvin by adding 273.

Answer 2

I think the question wants you to assume that all of the octane combusts. From the balanced equation if you have 1 mole of octane you can end up with 8 moles of CO2. So what you need to do is figure out how many moles 9.85g of octane is. Then figure out how many mole of CO2 you could get if all the 9.85 grams combusts. Solve pv =nrt for v and plug in the numbers.

p is given
r is given
t is given
all you need to figure out is n which is the number of moles of CO2.

Answer 3

mols octane = 9.85/(12*8+18) = 86.4*10^-3mol

we know that 1 mole of octane produces 8 mols of CO2 so:

mols CO2 = 9*86.4*10^-3 = 0.7776mols

V = nRT/P = 0.7776*8.314*298)/(1.01*10^5) = 19.1*10^-3 m^3

Answer 4

Knowing the mass of Octane convert to moles of Octane by dividing by its Mr (114).
Frrom your eq'n the molar ratios are 1:8; that is one mole of octane produces 8 moles of CO2.
So whatever value for moles of octane multiply that value by 8. This is the moles of CO2 produced.
The substitute the answer (moles CO2) for 'n' in the Ideal Gas Eq'n.
The 'p' is given
V is to be found
R is given
T is given but convert to Kelvin
The answer should be in m^3 (cubic metres).
pV = nRT is algebraically re-arranged to
V = nRT/p

Answer 5

convert the amount of grams of octane into moles. then use the ratios from the balanced equation to find the number of moles of carbon dioxide. Then use the pv=nRT equation to find the volume...

Answer 6

Im not doing your homework for you! You need to work out (at 25 degrees) what the volume of the CO2 produced is based on the number of molecules you have.

Answer 7

Why don't you do your own homework?