Consider these changes. (In notes) 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?

Question

(a) Hg(l) --> Hg(g)

(b) 3O2(g) --> 2O3(g)

(c) CuSO4 · 5H2O(s) --> CuSO4(s) + 5H2O(g)

(d) H2(g) + F2(g) --> 2HF(g)

Answer 1

Work is done when there is expansion or contraction. In these examples you are looking for formation of gas or more moles of gas for work done by the system. Work iby system 1, 3 and work on system 2