[Zyzz]

Hey,

I have this question regarding Hess law but I haven't been able to wrap my head around it, hopefully someone can enlighten me on how to go about it


An investigation was performed to test Hess's law.  A measured mass of cycloheptane was completely burned in a bomb calorimeter.  The following data was generated.

7C(s) + 7H2(g) --> C7H14(l)            Hf = -156.6 kJ/mol
C(s) + O2(g) --> CO2(g)                    Hf = - 393.5 kJ/mol
H2(g)  ½ O2(g) --> H2O(l)                Hf = - 285.8 kJ/mol

­Using the information from the investigation, what is the predicted molar enthalpy of combustion of cycloheptane?

[opti384]

First of all do you fully understand Hess's Law?

The next step will be writing the equation of combustion of cycloheptane.

[phoenixcelestius]

Basically Hess's Law says that you can manipulate chemical equations and their H_f (a lot like solving algebraic systems of equations with the elimination method) so that you get the final reaction and H_f that you want. That's a clue.