calculating enthalpy?

Question

Calculate the enthalpy change of the following reaction between nitrogen gas and oxygen gas, given thermochemical equations 1, 2 ,and 3 .

2N(2) + 5 0(2) ----->2H(2)0(5) AH = ?

1. 2H(2) + 0(2) ------>2H(2)0 AH = -572 kj/mol
2. N(2)0(5) + H(2)0 ---> 2HNO(3) AH = -77 kj/mol
3. 1/2 N(2) + 3/2 0(2) + 1/2 H(2) ---->HNO(3) AH = -174 kj/mol

Additional Details


Thanks for answering , and I follow u up to that point..I know what to do with equations #2 and #3 ... but I'm not sure what to do to equation #1 and why ?? How do i figure that out..I want to multiply it all by 5 , but this doesnt seem right ....help ! thanks

Answer 1

You multiply -572 by 5 because in the equation 5O2 reacts with 2H2and in the 1. equation there is only 1mol of O2.