Hess's Law - Chemical Ideas 4.1
Hess's Law
Hess's Law states as long as the start and end points of the reaction are the same, the enthalpy change for the chemical reaction will be the same, which ever route is taken from start to finish. This is useful for calculating unknown enthalpy change alongside other known enthalpy change.
Hess Cycles
Hess's Law states as long as the start and end points of the reaction are the same, the enthalpy change for the chemical reaction will be the same, which ever route is taken from start to finish. This is useful for calculating unknown enthalpy change alongside other known enthalpy change.
Hess Cycles
The picture above shows the calculated enthalpy change for the formation of hexane. The calculated value is -204.0 KJmol-1 and this is done by getting the two known enthalpy change values and adding them. Hess's law states that the enthalpy change in the formation of hexane is equal to using the alternate route enthalpy change.