so here's a more complicated kind of hess's law problem so what we want to do is we want to figure out what the heat of En or the enthalpy is uh for this reaction over here so let's first look at this and and kind of given these three fundamental reactions so first of all we look at these reactions and we know that we have Florine gas on the reactant side there's only one equation that has Florine gas in it so in this case we're going to have to go ahead and reverse this one and when we reverse this reaction we end up getting I'll write this over again 2f2 + O2 yield uh 20 F2 and our Delta H knot for 2 equals - 49.4 but we also know that we only need one Florine over here we have two here so we have to take this whole thing and cut it in half uh on here so if we end up cutting this in half we end up getting Florine plus2 yields o F2 and our Delta H KN of I I now equals um oh and the other thing is we also have to change a sign up here so we have to change a sign of this and then we end up cutting it in half is we end up getting a positive 2 uh uh 24.7 KJ so we reversed it and cut it in half so reversing it changes the sign and then we can cut our Delta H in half and that is purely because it's a state function then we look at this reaction we now know that we have um O2 and kind of uh thinking about this we know we want cf3 as a product we look over here the cf3 is there but we need to reverse that reaction so when we go ahead and reverse that reaction we end up getting uh 1 12 cl2o plus 3es o F2 ends up yielding CF uh CL F3 + O2 gas and our Delta H since we didn't change anything uh we reversed it it now becomes a negative to 36.2 K on here and then we can go ahead and take the third the other uh reaction oops sorry this was reaction four then we can look at our final our reaction three and we can take that reaction as is except we need to cut that in half so we end up getting um two clf plus O2 yeld cl2o plus o f 2 if we want to get rid of some of those kinds of reaction we know that we have to cut this in half so our Delta H now equals we did not change the direction so so we can still keep it as positive 24.0 we divided by that by two we end up getting 107 k 107.0 then what we can do is we can go ahead and take all these reactions and add them up if you actually add them all up you will find out that you get clf plus F2 yield clf3 and then our Del H now it's going to be the sum of all the reactions after we make the manipulations of all those reactions so this Delta H now equals 104.5 K so that is a more difficult kind of problem uh for hess's law