Enthalpy of a substance can be determined with the help of the formula mentioned below :

ΔH = ΔU + ΔngRT

where H denotes enthalpy , Δng denotes the changes in the number of gas species involved ibn a reaction , R is the universal gas constant and T is the temperature.

the balanced equation for the combustion of naphthalene is as follows:

C10H8 + 12O2 = 10 CO2 + 4 H2O

Here Δng = ( 10-14 )

Δng = -4

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

ΔH = ΔU

which means ΔH = 5133Kj/MOL - 4 * RT

ΔH = 5133 - 9.91 KJ/MOL

hence ΔH = 5142 KJ/MOL