State Functions and Bond Enthalpies

[Kathleen Vidanes 1E]

It seems that many of the concepts throughout chapter 8 go back to the idea of state functions. I am still having trouble understanding the meaning of a state function as well as its relationship to enthalpy. Can someone please explain how enthalpy is a state function and why one can use the difference between the standard enthalpy of formation of products - reactants to find the standard reaction enthalpy if bond enthalpies are not available?

[Felicia Fong 2G]

A state property is a value that is determined by its current state and is not dependent on the path taken to obtain that state. You can determine the change in enthalpy by calculating final - initial. So, you only need the enthalpy of the product and the enthalpy of the reactant to find the enthalpy of a reaction. Think of a mountain and calculating the change in altitude. You only need the final altitude(top of the mountain) - initial altitude(bottom of mountain). (and the curve of the path doesn't matter)

[Annalise Eder 2L]

On the other hand, path functions do depend on the path taken from initial to final state. One way to think about state functions is if you had a bank account with $1,000 in it and you took out $100 at once or $25 on four separate occasions, you would have $900 left in your bank account either way and the path taken did not affect this. Enthalpy is a state function and can be thought of mathematically as an integral that depends on the initial and final states but not how it go there.