3.2.1 Energetics - Simple applications of Hess's Law
Students should:
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Hess' Law
Hess' Law states that the total enthalpy change between given reactants and products is that same regardless of any intermediate steps (or the reaction pathway).
This basically means that energy changes can be calculated from other energy changes which may be found experimentally. It is the fundamental basis of nearly all the thermodynamic data that we have available today.
It is not possible in the majority of cases to calculate the formation enthalpy of a substance, whereas it is possible to find the combustion enthalpy by experimentation. In many cases historically it was possible to calculate the enthalpy of formation from the combustion enthalpies using Hess' law.
Any equations can be mathematically manipulated using the four rules of number to construct other equations.
