Homework Help: ap chem

Posted by Anonymous on Tuesday, March 15, 2011 at 12:09am.

The heat of combustion of propane is -2,220.1 kJ/mol
calculate the heat of formation, delta Hf, of propane given that delta Hf of H20= -285.3 kJ/mol and delta Hf of CO2 = -393.5 kJ/mol

ap chem - DrBob222, Tuesday, March 15, 2011 at 12:25am
C3H8 + 5O2 ==> 3CO2 + 4H2O
-2220.1 kJ/mol = (n*sum delta Hfproducts) - (n*sum delta Hfreactants).
The only unknown is delta Hf C3H8. You have the values for H2O and CO2. O2, of course, is zero.
ap chem - Anonymous, Tuesday, March 15, 2011 at 12:44am
so we multiply the sum by the total number of moles, or by moles of reactant and product separately?
ap chem - DrBob222, Tuesday, March 15, 2011 at 1:05am
The products are CO2 and H2O.
So it's [(3*deltaH CO2) + (4*deltaH H2O)] - (1*deltaH C3H8) = -2220.1 kJ and solve for deltaH propane.

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