Consider these changes.
(a) Hg (l) ---> Hg(g)
(b) 3O2(g) ---> 2O3(g)
(c) CuSO4 x 5H2O(s) ---> CuSO4(s) + 5H2O
(d) H2(g) + F2(g) ---> 2HF(g)
At constant pressure, in which of the reactions is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done?