Hess's Law

[Alysha Dijamco 3E]

Hello! I was looking over my notes, and I was having a little trouble understanding why we are able to use Hess's Law to find delta H. More specifically, why we are able to add the two reactions in order to get the delta H of a certain formation. Thank you!

[Tricia Tran 1G]

From the lectures, enthalpy is a state function, meaning that you are able to calculate the total change in enthalpy by adding up the enthalpies in each step. Therefore, Hess's Law works since you can find the total enthalpy of the final equation by adding up the enthalpies of multiple reactions together.

[705984987]

hi,
from what I understand, hess's law works because the answer to the problem (no matter how many reactions occur) will always be the same(which in known as a state function). In lecture (as well is in the book), he visualized it with the mountain/elevation analogy, so that may help in understanding.

[Gauri Gusain 3H]

Basically each equation that is given a step in order to the get to the final overall step. When the overall equation is broken down into many parts you can simply add the enthalpy values of those multiple parts to get the overall value.

[205750231]

In a certain reaction, there may be multiple processes that combine to form one reaction. Since enthalpy is a state reaction, we can use Hess' Law to add these enthalpies together to get the total enthalpy of the reaction.