Question

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 1

Correct Answer - 3
The given reaction on two solution mixing is
`CaCl_(2)+Na_(2)CO_(3) rarr CaCO_(3)+2NaCl`
Each` 100%` dissociated at infinite dilution, thus
`Ca_((aq.))^(2+)+2Cl_(aq.)^(-)+2Na_((aq.))^(+)+CO_(3(aq.))^(2-)rarr 2Na_((aq.))^(+)+2Cl_((aq.))^(-)+CaCO_(3(s))`
or `CO_(3(aq.))^(2-)+Ca_((aq.))^(2+)rarr CaCO_(3(s))`
`:. Delta_(r)H=Sigma_(Pr od uct)^(@)-Sigma_(reactant)^(@)`
`=Delta_(r)H^(@)Sigma_(CaCO_(3))^(@)-[Delta_(f)H^(@)Sigma_(Ca^(2+))+Delta_(f)H^(@)Sigma_(CO_(3)^(2-))]`
`=-288.46-(-129.80-161.65)`
`=2.99kcal~~3kcal`