Ca3(PO4)2 (s beta) + 3 H2SO4 (aq) → 2 H3PO4 (aq) + 3 CaSO4 (s)

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Stoichiometry

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Ca3(PO4)2      Mass: g
H2SO4          Mass: g  or Solution Volume: mL of Concentration: mol/L
H3PO4          Mass: g  or Solution Volume: mL of Concentration: mol/L
CaSO4          Mass: g

Enthalpy of Reaction

[2ΔHf(H3PO4 (aq)) + 3ΔHf(CaSO4 (s))] - [1ΔHf(Ca3(PO4)2 (s beta)) + 3ΔHf(H2SO4 (aq))]
[2(-1277.38) + 3(-1434.5)] - [1(-4120.82) + 3(-909.27)] = -9.63000000000102 kJ
-9.63 kJ     (exothermic)

Entropy Change

[2ΔSf(H3PO4 (aq)) + 3ΔSf(CaSO4 (s))] - [1ΔSf(Ca3(PO4)2 (s beta)) + 3ΔSf(H2SO4 (aq))]
[2(-221.75) + 3(106.5)] - [1(235.98) + 3(20.08)] = -420.22 J/K
-420.22 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[2ΔGf(H3PO4 (aq)) + 3ΔGf(CaSO4 (s))] - [1ΔGf(Ca3(PO4)2 (s beta)) + 3ΔGf(H2SO4 (aq))]
[2(-1018.8) + 3(-1322)] - [1(-3884.84) + 3(-744.63)] = 115.129999999999 kJ
115.13 kJ     (nonspontaneous)

From ΔG = ΔH - TΔS:
115.66 kJ     (nonspontaneous)

Equilibrium Constant, K (at 298.15 K)

6.74488156715118E-21
This process is not favorable at 25°C.

Reference(s):

Swaddle, T.W. Inorganic Chemistry; Academic Press: San Diego, 1997; p 186.

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