Question

Lithium iodide has a lattice energy of −7.3×102kJ/mol and a heat of hydration of −793kJ/mol. Find the heat of solution for lithium iodide. Determine how much heat is evolved or absorbed when 10.0g of lithium iodide completely dissolves in water.

Answer 1

113.6567 kiloJoules of heat is evolved or absorbed when 10.0 g of lithium iodide completely dissolves in water.

Step-by-step explanation:

Lithium iodide has a lattice energy =
`\Delta H_(lat)=-7.3* 10^2 kJ/mol`

Lithium iodide has a heat of hydration =
`\Delta H_(hyd)=-793 kJ/mol`

Heat of the solution of lithium iodide :

`\Delta H_(soln)=\Delta H_(lat)+\Delta H_(hyd)`

`=-7.3* 10^2 +(-793 kJ/mol)`

= -1,523 kJ/mol

Mass of lithium iodide = 10.0g

Moles of lithium iodide =
`(10.0 g)/(134 g/mol)=0.07462 mol`

Heat of the solution of lithium iodide when 0.07462 mol is dissolved: Q

`Q=Moles* \Delta H_(soln)=0.07462 mol* (-1,523kJ/mol)`

Q = -113.6567 kJ

(Negative sign indicates that energy released which means that temperature of the solution after dissolving lithium iodide will increase.)

Answer 2

Delta H of solution = -Lattice Energy + Hydration
Delta H of solution=- (-730)+(-793)
Delta H of solution= -63kJ/mol

Now we find moles of LiI:
10gLiI/133.85g=.075moles
multiply moles to the delta H of solution to cross cancel moles. .75moles x -64kJ/mol =4.7