Question

When 1 mole of methane burns in oxygen , the energy change is -890kJ. How much energy is given out when 1 gram of methane burns.(Ar:C=12,H=1)

Answer 1

Answer:

This is homogeneous combustion reaction i.e. the fuel (methane) and oxidant (oxygen) are in the same aggregate state (gaseous).

The energy value depends on whether the combustion is complete or incomplete.

And there are two values often considered here viz:

The Higher Calorific and

the Lower Calorific Value

For complete combustion, the reaction stoichiometry is

CH₄+ 2O₂ = 2H₂O + CO₂ ………………….(1)

And for incomplete combustion

CH₄+ 2O₂ = 2H₂O + CO, …………………., (2)

CH₄ + O₂ = 2H₂O + C,……………………….(3)

Let us, for simplicity, believe the combustion is complete and that we do not consider internal and external combustion ballasts, hence the Higher Calorific Value obtained from burning 1 gram of methane, applying Dulong’s Formula is:

1 gram of carbon will yield 8.1 kCalories (approximately 34.02 kJ) heat at 2235 oC while

1 gram of Hydrogen yields 30 kCal (approx. 126 kJ) of Heat at above temperature,

Therefore, the Higher Calorific values of burning 1 gram of methane following the reaction stoichiometry for complete combustion is

CH₄+ 2O₂ = 2H₂O + CO₂

Calculating the molar mass of methane CH₄ = C+ H*4 = 12 + 1*4 = 16

Therefore, Carbon constitutes 75% and Hydrogen is 25%

This brings the HCV (Higher or Gross Calorific Value) of methane, applying Dulong’s formular to:

HVC = 34.02[Cp/100] + 126 [Hp/100),

where Cp and Hp are percentage mass composition of Carbon and Hydrogen in Methane respectively

HVC of 1 gram of Methane = 34.02(0.75) + 126(0.25) = 25.515+31.5 kJ

Answer 2

Answer:

…

Explanation: