Lithium iodide has a lattice energy of -7.3 x 10 2 kJ·mol -1 (this much heat is

Question

Lithium iodide has a lattice energy of -7.3 x 102 kJ·mol-1(this much heat is released when a mole of LiI forms) and a hydration energy of -793 kJ·mol-1(this much heat is released with 1 mole of LiI formula units are hydrated). (These signs are negative, indicating exothermic processes.) Find the heat of solution for LiI in kJ·mol-1, and determine how much heat is evolved or absorbed when 15.0 g of LiI dissolves in 100 mL of water. If the water started out at 25 °C, what will the final temperature of the water be?

Explanation / Answer

Hsoln= H lattice(positive)+ H hydration(negative)=730 - 793= -63kJ/mole

Molar mass of LiI=7+127=134g

H soln for 15g LiI=63*15/134=-7.052kJ(exo)

Specific heat of H2O at 25°C(C)=4.1813J/g-K

Q=m*C*T

T=Q/m*C

=7.052 * 1000J/15*4.1813=112.4

T=112.4°C(change is equal in both °C and K)

Final temperature= 25 +112.4=137.4°C

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