CaSO4·2H2O(s) ⇄ CaSO4(s) + 2 H2O(g) The hydrate CaSO4·2H2O(s) can be heated to form the anhydrous sa — Thermodynamics Chemistry Question

ΔG° = Σ ΔG°f(products) − Σ ΔG°f(reactants)
= −1320.30 + (2 × −228.59) − (−1795.70 kJ mol−1)
= 18.22 kJ mol−1

One point is earned for the mole factor for water.
One point is earned for answer (units are optional).

ΔG° = ΔH° − TΔS°
ΔS° = (ΔH° − ΔG°) / T
= (105 − 18.22) kJ mol−1 / 298 K
= 0.29 kJ K−1 mol−1 OR 290 J K−1 mol−1

One point is earned for the correct substitution of ΔG°, ΔH°, and T.
One point is earned for the correct answer with correct units.

Kp = (p_H₂O)^2

One point is earned for the correct expression (use of partial pressure only).

Kp = (p_H₂O)^2 ⇒ 6.4 × 10^-4
p_H₂O = sqrt(6.4 × 10^-4) = 0.025 atm

One point is earned for the correct partial pressure (units are not required).

The p_H₂O at equilibrium at the new volume will be 0.025 atm.
Equilibrium vapor pressure is dependent on Kp , which in turn is a function of temperature, not volume. Because the temperature is still 298 K, the vapor pressure of H₂O remains 0.025 atm in the new volume.

One point is earned for the correct answer with justification.

molar mass of CaSO4·2H₂O(s) = 172.172 g mol−1
molar mass of CaSO₄(s) = 136.14 g mol−1
2.49 g CaSO4·2H₂O × (136.14 g CaSO₄ / 172.172 g CaSO4·2H₂O) = 1.97 g CaSO₄

One point is earned for the (rounded) correct molar masses.
One point is earned for an answer consistent with the molar masses.