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At 25^(@)C, 1 mole of MgSO_(4(s)) was dissolved in sufficient water, the heat evolved was found to be 91.2 kJ. One mole of MgSO_(4).7H_(2)O_((s)) on dissolution gives a solution of the same composition, accompanied by an absorption of 13.8 kJ heat. Calculate the enthalpy of hydration of MgSO_(4(s)). MgSO_(4(s))+7H_(2)O_((l))to MgSO_(4).7H_(2)O_((s))

Answer»

`-105` kJ/mole
`-77.4` kJ/mole
`+105` kJ/mole
`+77.4` kJ//mole

Solution :`(DeltaH_("SOL."))_("of ANHYDROUS salt")=(Delta H_("hyd."))_("of anhydrous")+(Delta H_("sol."))_("of HYDRATED salt")`
`-91.2=(Delta H_("hyd."))_("of anhydrous salt")+13.8`
`(Delta H_("hyd."))_("of anhydrous salt")=-91.2-13.8`
`=-105` kJ/mole


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