What is the sign of △S in the following reaction, CaSO4(s)➡️CaO(s) + SO3(g)

Answer 1

CaSO₄(s) ==> CaO(s) + SO₃(g)

Note that the left side of the equation has only a solid (low entropy).

The right side also contains a solid (low entropy) but in addition also contains a gas (high entopy).

Thus, the entropy of the products would be greater than that of the reactants and ∆S is positive.