Verified answer

It's products minus reactants. And yes, there is a situation where it changes

I have a discussion of products minus reactants right here:

http://www.chemteam.info/Thermochem/HessLawIntro2....

"Sometimes it changes and i get so confused"

The change happens when bond enthalpies are used. I have a discussion here:

http://www.chemteam.info/Thermochem/HessLawIntro3....

In the discussion, I solve a problem and n the problem discussion, I discuss how Hess' Law gets changed around to be reactants minus products. I then solve the exact same problem again using the now-changed formulation of Hess' Law.

I hope this helps with your confusion.

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is always sum of PRODUCT minus sum of REACTANT