THE HEAT OF COMBUSTION OF METHANE AT CONSTANT VOLUME IS MEASURED IN A BOMB CALORIMETER AT 298K AND IS FOUND TO BE -885KJ/MOL. CALCULATE THE HEAT OF COMBUSTION AT COSTANT PRESSURE.

Heat released at constant pressure is known as enthalpy.

Enthalpy of any substance can be determine with the help of the formula mentioned below:

ΔH = ΔU + Δn_{g}RT

Where H denotes enthalpy, U is internal energy, Δn_{g }denotes change in the number of gases species involved in a reaction, R is the universal gas constant and T is the temperature.

The balanced equation for the combustion of methane is as follow:

CH_{4} + O_{2 }→ CO_{2} + 2H_{2}O

Here Δn_{g} = ( 1-3)

Hence Δn_{g} = -2

On substituting the above value in equation of enthalpy, we get

ΔH = -885 -2RT

ΔH = -885 - 4.95 KJ per mole.

Hence ΔH = -889.95 KJ per mole.

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