For the reaction, `A+B to D, DeltaH` is -30 kJ. Suppose, D is prepared from A and B and then it is again converted into A and B by following the stages `D to E A+ B`. Calculate the total enthalpy change in these two stages ?

Explanation

`A+BtoD,DeltaH=-30kJ` . . (1)
The process `DtoEtoA+B` comprises the following two steps: `DtoE` . . . [2] and `E to A+B` . .. [3]
Overall reaction: `D to A+B` . . .[4]
The reaction [4] is the opposite of the reaction [1]. So, the enthalpy change in reaction [4] is +30 kJ. hence, the total enthalpy change in steps [2] and [3] is +30 kJ.