Let say capacitance of two identical capacitors be
C and they are charged through a potential
V1 and
V2, respectively.
After connecting in parallel,
Net potential difference,
= Which is not equal to the sum of individual initial potential difference, i.e.
VC≠V1+V2.
For an isolated system, charge remains always conserved.
i.e. sum of initial charge
= sum of final charge
Since, potential difference across each capacitors are different and connected in parallel, so charge redistribution will take place from higher potential capacitor to lower potential capacitor. As we know that if charge flow, then there is some loss of energy in form of heat.
i.e.,
Uf<Ui