Table 2.

Thermodynamic Cycle to Calculate (MgSO₄·nH₂O), n=3, 4

Reaction		Enthalpy (kJ·mol−1)
1	α-MgSO4 (cr)= (aq)	−85.52a±0.91b (3)c
2starkeyite	MgSO4·4H2O (cr)= (aq)	−18.45±0.17 (5)
2trihydrate	MgSO4·3H2O (cr)= (aq)	−21.01±0.79 (2)
3	H2O (l)=H2O (aq)	0
4	Mg (cr) + S (cr) + 2O2 (g)=α-MgSO4 (cr)	−1288.5±0.5d
5	H2 (g) + ½O2 (g)=H2O (l)	−285.8±0.1e
6starkeyite	Mg (cr) + S (cr) + 4O2 (g) + 4H2 (g)=MgSO4·4H2O (cr)	−2498.7±1.1
6trihydrate	Mg (cr) + S (cr) + 3.5O2 (g) + 3H2 (g)=MgSO4·3H2O (cr)	−2210.3±1.3

^aAverage.

^bTwo standard deviations of the mean.

^cNumber of measurements.

^dKo and Daut (1979), DeKock (1986).

^eRobie and Hemingway (1995).