Mg3(PO4)2 (s) → 3 Mg+2 (aq) + 2 PO4-3 (aq)

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Reaction Type:

Dissociation of an ionic compound in water

Enthalpy of Reaction

[3ΔHf(Mg+2 (aq)) + 2ΔHf(PO4-3 (aq))] - [1ΔHf(Mg3(PO4)2 (s))]
[3(-466.85) + 2(-1277.38)] - [1(-3780.66)] = -174.650000000001 kJ
-174.65 kJ     (exothermic)

Entropy Change

[3ΔSf(Mg+2 (aq)) + 2ΔSf(PO4-3 (aq))] - [1ΔSf(Mg3(PO4)2 (s))]
[3(-138.07) + 2(-221.75)] - [1(189.2)] = -1046.91 J/K
-1,046.91 J/K     (decrease in entropy)

Free Energy of Reaction (at 298.15 K)

From ΔGf° values:
[3ΔGf(Mg+2 (aq)) + 2ΔGf(PO4-3 (aq))] - [1ΔGf(Mg3(PO4)2 (s))]
[3(-454.8) + 2(-1018.8)] - [1(-3538.83)] = 136.83 kJ
136.83 kJ     (nonspontaneous)

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

Equilibrium Constant, K (at 298.15 K)

1.06435687458039E-24
This process is not favorable at 25°C.

Enter an initial concentration for the ionic compound. Upon hitting submit, Ksp (1.06435687458039E-24) will be used to calculate the equilibrium concentration for all species.

Mg3(PO4)2 Mg+2 PO4-3
Initial M   0 0
Change -x +3x +2x
Equilibrium