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Calculate the standard enthalpy of precipitation of CaCO3(s) in kcal/mol for the reaction: Ca²+(aq) + CO3²-(aq) -> CaCO3(s). Given: delta_f H(Ca²+, aq) = -130 kcal/mol, delta_f H(CO3²-, aq) = -160 kcal/mol, delta_f H(CaCO3, s) = -285 kcal/mol.
- -25
- -35
- -45
- -55
Correct answer: -25
Solution
The enthalpy of the precipitation reaction equals the standard enthalpy of formation of CaCO3 minus the sum of enthalpies of formation of the ionic reactants.
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