Chemistry - Thermochemistry Question with Solution | TestHub
In order to get maximum calorific output, a burner should have an optimum fuel to oxygen ratio which corresponds to 3 times as much oxygen as is required theoretically for complete combustion of the fuel. A burner which has been adjusted for methane as fuel (with 'X' l/hr of methane and '6X' l/hr of oxygen) is to be adjusted for propane. In order to get same calorific output, what should be the supply of oxygen (in l/hr) with 1 l/hr supply of propane? Assume that losses due to incomplete combustion, etc., are the same for both fuels and that the gases behave ideally. Enthalpies of combustion; methane = -880 kJ/mol; propane = -2200 kJ/mol.
Answer:
Solution:
For propane, C3H8 + 5O2 → 3CO2 + 4H2O, so optimum O2 = 3 × 5 = 15 l per l of propane. Equal calorific output: y × 2200 = X × 880 gives y = 0.4X l/hr propane. O2 supply = 15 × 0.4X = 6X l/hr, i.e. 6 l/hr per l/hr of propane. Answer: 6.
