One kg of graphite is burnt in a closed vessel. The same amount of graphite is burnt in an oepn vessel. Will the heat evolved in the two cases be the same ? If not, in which case it would be greater?

Explanation

Burning of graphite involves the following reaction
C(graphite)`+O_(2)(g)toCO_(2)(g)`.
In an oepn vessel, if a reaction is carried out, it occurs at constant atmospheric presses. So, in the reaction, the heat change in the samme as the enthalpy change `(DeltaH)`. the heat change in a reaction carried out in a closed vessel at constant volume is the same as the internal energy change `(DeltaU)`.
For the above reaction, `Deltan=1-1=0`. thus, according to the relation, `DeltaH=DeltaU+DeltanRT`, we have `DeltaH=DeltaU`. therefore burning of 1 kg of graphite will produce the same amount heat irrespective of whether the reaction is carried out constant volume or at constant pressures..