Calculate the enthalpy change when infinitely dilute solutions of `CaCl_(2)` and `Na_(2)CO_(3)` are mixed. `Delta_(f)H^(@)` for `Ca_((aq.))^(2+),CO_(3(aq.))^(2-)` and `CaCO_(3(s))` are `-129.80,-161.65` and `288.46kcal//mol` respectively.

Answer

4 KCAL

Explanation

On mixing `CaCl_(2) (aq)` and `Na_(2)CO_(3)`
`CaCl_(2) + Na_(2)CO_(3) rarr CaCO_(3) + 2NaCl`
solutions are very dilute and thus, 100 % dissociation occurs. `Ca^(2+) (aq) + 2Cl^(-) (aq) + 2Na^(+) (aq) + CO_(3)^(2-) (aq) rarr`
`CaCO_(3) darr + 2Na^(+) (aq) + 2Cl^(-) (aq)` or
`Ca^(2+) (aq) + CO_(3)^(2-) (aq) rarr CaCO_(3) (s)`
`:. DeltaH = SigmaH_("Products")^(0)` or `Delta H = DeltaH_(f CaCO_(3))^(0) - [Delta H_(f ca^(2+))^(0) + Delta H_(f CO_(3)^(2))^(0)]`
`:. H^(0)` of a compound
`= H_("Formation")^(0) = - 288.45 - (-129.80 - 161.65) = 3 k cal`