Question

`100` gm of anhydrous `CuSO_(4)`, when dissolved in excess of water produces `42` kJ of heat. The same amount of `CuSO_(4).5H_(2)O` on dissolving in large excess of water absorbed `4.60` kJ. What is the heat of hydration `CuSO_(4)`?

Answer 1

100 gm of `CuSO_(4)=100/159.5` mole
Heat of solution of `CuSO_(4)` per mole `= - (42xx159.5)/(100)= -66.99 kJ rArr -67 kJ`
`100` gm of `CuSO_(4). 5H_(2)O=(100)/249.5` mole
Heat of solution per mole `(CuSO_(4). 5H_(2)O)=4.6xx 249.5/100 =11.477 kJ`
`{:("Now,",CuSO_(4)(s)+aq. rarr CuSO_(4)(aq)," "Delta_(r)H= -67" kJ mol"^(-1)),(,CuSO_(4)(aq) rarrCuSO_(4).5H_(2)O+aq," "Delta_(r)H=-11.477" kJ mol"^(-1)),(,bar(CuSO_(4)^(s)+5H_(2)O rarr CuSO_(4).5H_(2)O," "Delta_(r)H=-78.477" kJ mol"^(-1))):}`
`:.` Enthalpy of hydration of `CuSO_(4)(s), DeltaH= -78.477 kJ mol^(-1)`