Using Hess law

[arielle_cunanan3K]

I thought since enthalpy is a state function, we only care about it’s final and initial value, not the intermediate steps. If that’s so, why are we using Hess law to calculate the delta H of reaction by adding the delta H at the intermediate steps in a multi step reaction?

[Chris Korban 1D]

We are able to do this because those may be intermediate values for the whole equation, however the Enthalpies we get for each individual reactant and product are the basic foundations for the total Enthalpy of the Reactants and the total Enthalpy of the products and they are the final Enthalpies for those steps, so it is like adding final values of the building blocks of the whole reaction

[RobinFong_2B]

For a state function, we are only concerned with the variable's current state. So in order to find the value of the current state we have to add or subtract the intermediate steps. A characteristic of a state property is that they can be added or subtracted.

[Nishan Reddy 3K]

Hess' law further emphasizes the fact that enthalpy is a state variable because we can simply add or subtract the enthalpy of two or more reactions to find the enthalpy of the overall reaction. Thus, we do not need to know how the final enthalpy was achieved, it doesn't matter how the steps occurred only that the steps resulted in the final composition we want.

[gracebinder3I]

Hi!
A state property does mean that the path taken doesn’t matter, but does not specify that intermediate steps do not matter. Those steps are still important because their enthalpies help us use addition to form the net reaction from the multi-step process of Hess’s Law.
I hope this helps!

[Omer_Abdelrahim_1B]

I believe that the problem solving based around Hess's law is finding those intermediate steps so that you can take the final and initial values and subtract them from themselves.

[Riya Sawhney 1C]

The reactions we add up when using Hess's law are not necessarily intermediate reactions. Yes, the components will cancel out like intermediates, but since the change in enthalpy is pathway independent, the reaction does not have to be carried out just like this for it to happen.

[Isabelle Kim 3E]

To start off with, Hess’s Law states that it doesn’t matter what path is taken to reach the final enthalpies in a chemical reaction. And so, we can solve for the TOTAL enthalpy in more than one way (if needed). We can solve for it directly or break down the chemical reactions into smaller ones and get the sum of all the calculated enthalpies.

[lily_oneal_2B]

I don't think it is that we are neccesarily trying to find the enthalpy for the intermediate steps. Rather, we are using the smaller steps in order to find the final enthalpy, which is what we are concerned with.

[Lawrence Tran 2H]

We use those intermediate steps to find what the total enthalpy change would be, and it is still a state function since those order of steps and the path it took doesn't really matter, the intermediate steps are just the constituent parts of the whole reaction

[Samir Panwar]

Since a characteristic of a state property is that they can be added or subtracted, we can then use the intermediate steps to calculate the enthalpy change, as the path to get the final enthalpy in a reaction does not matter.

[Kimberly_martinez2I]

Because a state property can be added or subtracted, in order to find the final enthalpy we can use the intermediate steps.

[Myra Goraya Dis 2E]

we utilize the intermediate steps by adding them together, which is only possible because enthalpy is a state function

[SerenaSabedra]

State properties aren't defined by anything other than its current state, so if you wanted to calculate the enthalpy of a system with multiple molecules, you can add together all of the enthalpies because they make up the total system.

[Lesley Kim 1K]

Intermediate steps are also helpful when you don't know the value of enthalpy of the final step of a reaction, but are given the value of enthalpy for all the needed intermediate steps.