Calcium hydroxide dissolves slightly in water according to the equation
Ca(OH)₂(s) → Ca²⁺(aq) + 2 OH⁻(aq)
Standard molar entropies at 298 K are given below.
Species S° (J·mol⁻¹·K⁻¹)
Ca(OH)₂(s) 83.4
Ca²⁺(aq) −53.1
OH⁻(aq) −10.5
Assume that the activities of all aqueous species are unity.
a. Part 1: Write the balanced dissolution equation shown above in words, identifying the physical state of each species.
b. Part 2: Calculate the standard entropy change ΔS∘ for the dissolution process at 298 K.
c. Part 3: The standard enthalpy change for dissolution is ΔH∘=+16.7kJmol−1. Compute the standard Gibbs free-energy change ΔG∘ at 298 K and determine whether the dissolution of Ca(OH)₂ is thermodynamically favorable under standard conditions.
d. Part 4: Discuss two factors, other than the sign of ΔG∘, that influence the observed solubility of Ca(OH)₂ in water at room temperature.