Posted by Samantha on .
How would you calculate delta H for the following reaction:
2P + 5Cl2 > 2PCl5
Given:
PCl3 + Cl2 > PCl5 Delta H=87.9 kJ
2P + 3Cl2 > 2PCl3 Delta H=574 kJ
I have no clue how to do this since I was absent. Can someone help?

Chemistry 
DrBob222,
Look up Hess' Law.
Multiply equation 1 by 2 and add it to equation 2. Multiply delta H for equation 1 by 2 and add to delta H for equation 2.