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 + ΔngRT
Where H denotes enthalpy, U is internal energy, Δng 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:
CH4 + O2 → CO2 + 2H2O
Here Δng = ( 1-3)
Hence Δng = -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.