Answer to Question #6461 in Physical Chemistry for Smirky

Question

Molar volume of an ideal gas at S.A.T.P. (25oC and 1.00 bar is 24.8 dm3 mol-1. Assume that gases are at 225oC and P=1.00 atmosphere before and after the combustion and behave as ideal gases.
The chemical equation for the combustion of butane is:
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(l)

At 225oC, we ignite a mixture of 5.00 dm3 of butane and 75.0 dm3 of O2

i. Is there enough oxygen for the complete combustion of the butane present?
ii. What gases are present in the resulting mixture after combustion?
iii. Calculate the final volume of the mixture after combustion (3 sig. fig).
Iv. Calculate the amounts (number of moles) of O2 and butane consumed using the molar volume of an ideal gas at S.A.T.P (3 sig. fig).
v.The final mixture is cooled down from 225oC to 25oC. Calculate the volume of the resulting gaseous mixture (3 sig. fig.).

Answer 1

5.00 dm3 x1 x2
2C₄H₁₀(g) + 13O₂(g) → 8CO₂(g) + 10H₂O(l)
2 13 8

Volume of O₂ x₁ = 5*13/2 = 32.5
Volume of CO₂ x₂ = 5*8/2 = 20

1. Yes ,we need 32.5 and we have 75
2. O₂ and CO₂ (C₄H₁₀ burns completely)
3. x₁ + x₂ = 75 - 32.5 + 20 = 57.5
4. For O₂ it 32.5/24.8 = 1.31 moles and for C₄H₁₀ it 5/24.8 = 0.202 moles
5. P = const; V₁/T₁ = V₂/T₂
42.4*(273 + 25)/(273 + 225) = 25.43