ThermochemistryHard

Question

The lattice energy of Na2CO3(s) is 205 kJ/ mol and the hydration energies of Na+ and CO32− ions are −80 and −40 kJ/ mol, respectively. The correct prediction about the solubility of Na2CO3 in water is (Assume that ΔH is independent of temperature)

Options

A.increases with increase in temperature.
B.decreases with increase in temperature.
C.unaffected by the change in temperature.
D.first increases and then decreases with increase in temperature.

Solution

$\Delta_{solution}H = 205 + \left\lbrack ( - 80) \times 2 + ( - 40) \right\rbrack = + 5\text{ kJ/mol}$

As the solubility is endothermic, it should increase with increase in temperature.

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