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

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

Answer 2

Answer:

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

Explanation:

Lithium iodide has a lattice energy = $\Delta H_{lat}=-7.3\times 10^2 kJ/mol$

Lithium iodide has a heat of hydration = $\Delta H_{hyd}=-793 kJ/mol$

Heat of the solution of lithium iodide :

$\Delta H_{soln}=\Delta H_{lat}+\Delta H_{hyd}$

$=-7.3\times 10^2 +(-793 kJ/mol)$

= -1,523 kJ/mol

Mass of lithium iodide = 10.0g

Moles of lithium iodide = $\frac{10.0 g}{134 g/mol}=0.07462 mol$

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

$Q=Moles\times \Delta H_{soln}=0.07462 mol\times (-1,523kJ/mol)$

Q = -113.6567 kJ

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