Cesium chloride has a lattice energy - 657.0 kJ/mol and a heat of hydration of - 639.0 kJ/mol. Determine how much heat is evolved or absorbed when 30.0 g of cesium chloride completely dissolves in water.

Q = 3.21 kJ

Explanation:

First, with the heat of hydration and the lattice energy, we can actually calculate the difference between those two to get the heat evolved per mole. In this case it would be:

657 - 639 = 18 kJ/mol

Now, the expression to get the heat is:

Q = m*ΔE

We already have the energy, now we need to get the moles of the cesium chloride.

The molar mass of cesium chloride is 168.36 g/mol, so the moles:

mole = 30/168.36 = 0.1781 moles

Finally the heat:

Q = 0.1781 * 18

Q = 3.21 kJ