Question

a gaseous hydrocarbon reacts completely with oxygen gas to form carbon dioxide and water vapor. given the following data, determine (delta)HoF for hydrocarbon:
(delta)Horxn=-2044.5kj/mol hydrocarbon
(delta)HoF CO2= -393.5kj/mol
(delta)HoF H2O = -242kj/mol
denstity of CO2 and H2O product mixture at 1 atm, 200celcius= .751g/L
the density of hydrocarbon is less than the density of Kr at the same cond.

Answer 1

Isn't delta H rxn = (delta H products)-(delta H reactants)? That will give you delta H for the hydrocarbon. Check my thinking.
I think the density information is extraneous information unless there is more to the problem than you posted.