Question

Given the following chemical reactions and their respective enthalpy changes

C2H2 + 5/2 O2-------- 2CO2 +H2O -1299.6 KJmol
C + 1/2 O2----------CO2 -393KJmol
H2 + 1/2 O2--------H2O -285.9KJmol

Calculate the Delta H for the reaction

2C + H2--------C2H2

Answer 1

Note your equation 2 is not balanced. It should be C + O2 ==> CO2. I don't know if dH is correct or not. Check it. This is eqn 2.
What you want to do is this.
Add 2 times eqn 2 to eqn 3 and to the reverse of eqn 1. If you multiply an equation you must multiply the dH value too. If you reverse an equation you must use the negative of dH for that eqn.
Check to make SURE that these manipulations will give you the new eqn you want.

Answer 2

11113