The enthalpy for a reaction depends only on the difference between the enthalpy of the products and the enthalpy of reactions. It is independent of the route by which the reaction may occur.
The enthalpy change for a reaction is the sum of the individual enthalpy changes for each step.
H1 = H2 + H3 = H4 + H5 + H6
Hess's law is particularly useful for determining the enthalpy change for a reaction that is difficult to measure directly.
It is important to realize that a reaction can be reversible and the enthalpy simply changes sign. Furthermore, take notice on the different moles. If a reaction requires two moles, simply times the reaction enthalpy by two.
These are a few examples:
No comments:
Post a Comment