I have been racking my brain for some time with this problem, I see what I have to do and I really think I get an answer but it’s continually not right. The problem is as follows:

Propane, C3H8(g), is used in many instances to produce heat by burning: C3H8(g) + 5O2(g) -->3CO2(g) + 4H2O(g) The standard enthalpy of reaction is -2,044 kJ. How many grams of oxygen would be needed to produce 605.0 kJ of heat? The answer needs to be in scientific notation.

I have tried various stoichiometry setups and I get nothing. I am not even sure what units go with what to be honest. I am trying to find grams of oxygen, but I don't even know what I have to start with. I have tried the following:

605.0 kJ x 1 mol x 16.00 g O2 / 2044 kJ x 5 mol O2

605.0 kJ x 1 mol x 32.00 g O2 / 2044 kJ x 5 mol O2

I have tried starting with the 2044 kJ and still nothing. I have also tried:

605.0 kJ x 1 mol x 16.00 / 1 kJ x 5 mol

605.9 kJ x 1 mol x 32.00 / 1 kJ x 5 mol

I have tried other various things with this as well trying to include the C3H8 in there to see what happens including using its formula weight of 44.01, but it seems nothing works.

I am missing something, I know I am. It is right there and I can't see it. I was able to get the other problems for my homework without any problems, even some of the harder Hess' Law problems, but this is just baffling me. Perhaps it’s because its 12:40 A.M. Any guidance or direction anyone could give me would be appreciated.