Question

The alkali metals react with chlorine to give salts:

2Li(s) + Cl2(g) → 2LiCl(s)

2 Na(s) + Cl2(g) → NaCl(s)

2 K(s) + Cl2(g) → KCl(s)

2 Rb(s) + Cl2(g) → RbCl(s)

2 Cs(s) + Cl2(g) → CsCl(s)

Using the data in Table 1, compute ∆H°, ∆S°, ∆G° of each reaction and identify a periodic trend, if any.

Answer 1

Lithium

∆H0 =∆Hf (product) - ∆Hf( reactant)

= -408.3KJ/mole - (0)

= -408.3 KJ/mole

∆S0 = S0(product)-S0(reactant)

= 2×58.3J/mole K - (165.2(J/moleK)+ 2×29.12(J/K mole)

= -106.8J / mole K

∆G = ∆H - T∆S

= -408300J - (298.15K ×(- 106.8J/K))

   = -376.5KJ

Sodium

∆H0 = - 411.12 - (0+0)

   = 411.12 KJ / mole

∆S0 =2× 72.11(J/mole K)-( 165.2 (J/mole K)+2×51.3(J/K mole)

= -123.58J/K mole

∆G0 = 411120 J - (298.15× (-123.58))

= -374.2KJ

Similarly you can calculate the value and understand the periodic trend