1. To do or not to do?---------That is a question too….
Qn. 10
To do or not to do? That is a question too….
Liu Jiani Sherry (14)

2. a) L.E.:
It is the energy evolved when 1 mole solid ionic compound formed from its gaseous constituents.
WHY?

3. Standard conditions Why solid?
Recall what is missing from the definition?
Ionic compounds are operationally defined as solids at stp, with the exceptions of a few composed of cation and anionic complex….
Standard conditions

4. Why gaseous constituents?
L.E. refers to the energy released from a bond formation. In gaseous state, ions have minimal interaction when they form the solid. So they bond energy evolved is then a good indication of the actual strength.

5. b) LE is proportional to (q+ * q-)/ (r+ + r-)
Charges of Li =Na
Ionic radius of Li > Na
smaller inter-ionic distance between LiCl and bigger electrostatic forces of attraction between its ions
Thus, larger magnitude and more exothermic.

6. When a bond forms, PE is released as KE.

7. -L.E: Solid ionic compound to gaseous ions
Delta E of solution: dissolution of ionic compound in water to get aqueous ions
Delta E of Hydration: hydration of individual gaseous ions to form Ion-Dipole interactions with water

8. Energy/ KJ per mol Li+ (g)+ Cl- (g) ∆H hyd (Li+) =-499
∆H hyd (Li+) =-499
L.E of LiCl=-848
Li+ (aq)+ Cl- (g)
∆H hyd (Cl-) =-381
LiCl (s)
∆H sol LiCl(s) =-36
Li+ (aq)+ Cl- (aq)
∆H sol LiCl(s) = -L.E.+∆H hyd (Li+) + ∆H hyd (Cl-)
=848 + (-499) + (-381)
= -36KJ/mol

9. Energy/ KJ per mol Na+ (g)+ Cl- (g) L.E of NaCl=-776
L.E of NaCl=-776
∆H hyd (Na+) =-390
Na+ (aq)+ Cl- (g)
∆H hyd (Cl-) =-381
Na+ (aq)+ Cl- (aq)
∆H sol NaCl(s) =+5
NaCl (s)
∆H sol NaCl(s) = -L.E.+∆H hyd (Na+) + ∆H hyd (Cl-)
=776 + (-390) + (-381)
= +5KJ/mol

10. Last part… Final temp. solution=? Q=mc ∆T
-36000J/mol * [1.0/( )]mol
= (100*4.2* ∆T)J
∆T=2.02 degree celsius
Final temp.=298K+2.02K
=300.02K
=300K (3sf)