Question

144 grams of C5H12 is burnt with 64 grams O2, and 44 grams of CO2 is formed, what is the percentage of excess O2?

(a) 25%

(b) 50%

(c) 75%

(d) 100%

I had been asked this question during an interview for a job.

Query is from Material Balances Involving Combustion in division The Chemical Reaction Equation & Stoichometry, Material Balances for Processes Involving Reaction and Multiple Units of Basic Chemical Engineering

Answer 1

Correct option is (a) 25%

The explanation is: The balanced chemical reaction is C5H12 + 8O2 -> 5CO2 + 6H2O, => Extent of reaction = (44/44 – 0)/5 = 0.2. Moles of O2 entered the process = 64/32 = 2, Moles of O2 required = 0.2*8 = 1.6, => Percentage of excess oxygen = 100*(2 – 1.6)/1.6 = 25%.