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The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at

constant pressure at the same temperature


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
which means ΔH = 5133Kj/MOL - 4 * RT

ΔH = 5133 - 9.91 KJ/MOL
hence ΔH = 5142 KJ/MOL
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