DF 2 

For some reactions, measuring enthalpy change is evry straightforward, however in some cases it is less simple ( it may need an extremely high temperature for it to occur). In cases like this, enthalpy changes can be measured indirectly using enthalpy cycles

==Hess’ law== – the enthalpy change for any reaction is independent of the intermediate stages, so long as the initial and final conditions are the same for each route