Homework Help: chemistry

Posted by lavonne on Tuesday, November 23, 2010 at 4:52pm.

Ok, I really need to know how to work problems like these so could someone please show me how to set it up?! Given this data:
1. C(graphite) + O2(g) produces CO2(g), delta H = -393.5 kJ
2. H2(g) + 1/2 O2(g) produces H2O(l), delta H = -285.8 kJ
3. Ch3OH(l) + 3/2 O2(g) produces Co2(g) + 2H2O(l), delta H = -726.4 kJ
Given these calculate the enthalpy change for:
C(graphite) + 2H2(g) + 1/2 O2(g) produces CH3OH(l)Please help!

chemistry - DrBob222, Tuesday, November 23, 2010 at 5:52pm
Use equation 1 as is. (delta H as is)
Add 2x equation 2 (and 2x delta H).
Reverse equation 3 and add to the other two (change the sign on delta H).
Then added the equations as noted and confirm you obtain the desired equation; finally, add the delta Hs (with changes as noted).

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