Question

Ethene is burnt with 50% of excess air, what is the percentage of CO2 in the products?

(a) 11.11%

(b) 36.36%

(c) 66.66%

(d) 72.72%

This question was addressed to me during a job interview.

My enquiry is from Material Balances Involving Combustion topic in section The Chemical Reaction Equation & Stoichometry, Material Balances for Processes Involving Reaction and Multiple Units of Basic Chemical Engineering

Answer 1

The correct choice is (b) 36.36%

For explanation I would say: The reaction is C2H4 + 3O2 -> 2CO2 + 2H2O. Basis: 10 moles of C2H4, => moles of O2 reacted = 30, => moles of O2 entered the process = 45, => moles of CO2, H2O and O2 in products are 20, 20 and 15 respectively, => percentage of CO2 = 20/55*100 = 36.36%.