Answer to Question #21205 in Physical Chemistry for EKANSH

Question

Q. A gas mixture of 3 litres of propane and butane on complete combustion at 25'C produces 10 litres of CO2. Initial composition of propane and butane in the gas mixture is-
(i) 66.66%,33.33% (ii) 33.33%,66.66% (iii) 50%,50% (iv) 60%,40%

Answer 1

The reactions propane and butane with oxygen:

C₃H₈ + 5O₂ --> 3CO₂ + 4H₂O

C₄H₁₀ + 6.5O2 --> 5H₂O + 4CO₂

If volume of propane is x , the volume of butane is 3-x. Than
volume of CO₂ is

x 3x
C₃H₈ + 5O₂ --> 3CO₂ + 4H₂O

(3-x) 5*(3-x)
C₄H₁₀ + 6.5O₂ --> 5H₂O + 4CO₂

Total volume of CO₂ is:

3x + 4*(3-x) = 10
3x + 12 - 4x = 10
-2x = -2
x = 2

Initial composition of propane is 2.0/3*100 = 66.66%
Initial composition of butane is 33.34%