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 butane. In order to get same calorific output, what should be the supply of oxygen (in l/hr) with 1 l/hr supply of butane? Assume that losses due to incomplete combustion, etc., are the same for both fuels and that the gases behave ideally. Enthalpies of combustion; methane = -800 kJ/mol; butane = -3120 kJ/mol.
Answer:
Solution:
For butane, the combustion reaction is:
C4H10 + 6.5O2 tarrow 4CO2 + 5H2O
From this, the optimum oxygen (O2) required is 6.5 × 3 = 19.5 liters per liter of butane.
To achieve equal calorific output, we use the equation y × 3120 = X × 800, which simplifies to y = 0.2564X liters/hour of butane.
The oxygen (O2) supply is then calculated as 19.5 × 0.2564X = 5X liters/hour. If the butane supply is 1 liter/hour (i.e., X=1), then the oxygen (O2) required is 5 liters/hour.
The final answer is 5.
