[Amina]

I've looked around and I'm finding it hard to grasp Hess' Law. I need to find the heat of combustion for Methanol and use delta H = -239.2
I am also using this equation:
2CH3OH + 3O2 --> 2CO2 + 4H2O

If anyone can help and take me through it step by step?
Thanks.

[Vidya]

write equations for the heats of formations of CH3OH ,CO2 and H2O

Enthalpies of formations of these compounds can be taken from the reference tables .
Combine the equations to get the desired equation
Try it 

[Amina]

I've tried writing the equations, but I don't think I've done them right:

2CH3OH --> 2C + 2H2 + 02 = H +478.4
2C + 2O2 --> 2CO2 = H -787
4H2 + 2O2 --> 4H2O = H - 967.2

They just seem wrong when I go to cross them out.

[Amina]

I've tried writing the equations, but I don't think I've done them right:

2CH3OH --> 2C + 2H2 + 02 = H +478.4
2C + 2O2 --> 2CO2 = H -787
4H2 + 2O2 --> 4H2O = H - 967.2

They just seem wrong when I go to cross them out.

I see what I did wrong there :3 Never mind, I've answered it. And sorry, I don't know how to edit the post