The experimental result of the standard change in enthalpy for the combustion reaction is 281.93 kJmol^{-1} at 1200K. Find its standard change in enthalpy at 298.15K given:

According to Hess’ law,

At 1200K,

At 298.15K,

Subtracting eq71 from eq70,

Since all species in the reaction are in the gaseous state from 298.15K to 1200K, we can substitute eq66 in eq72,

Substituting eq68 in the 1^{st} integral on the RHS of eq73,

Substituting the relevant values from the table above in eq73 and evaluating the integral (using the form expressed by eq74 for each integral in eq73),

and

Combining eq66 and eq69, for a reaction