Question

Look for the Sº of the reactants and products. Compute for the AS of the reactions.

1. 4Al(s) +302(g) → 2Al2O(s)

2. Agz Sis) 2Ag* (aq) + S²² (aq) 3. C₂H) +502(g) → 3C02(g) + 4H2O(g)

Answer 1

The standard entropy change, $\Delta S^o$ , for the following reaction :

${\Delta S^o_{rexn}=\Delta S^o_{pro}-\Delta S^o_{rec}}$

1)

4Al(s) + 3O₂(g) → 2Al₂O₃(s)

Given:

S^o[Al(s)] = 28.32 , s°[O₂(g)] = 205, Sº[Al₂O₂(s)] = 51.0 J /mol K

=51-(205+28.32)

=182.32

2)Ag2S(s)= 2Ag* (aq) + S²- (aq

S^o (J/Mol K)

Ag₂S=144

Ag+(aq)=72.6

S^2-=-14.6

$\Delta_rS=(2\times72.6-14.6)-144$

=-13.4

3)C3H8 +502(g) → 3C02(g) + 4H2O(g)

Given:

S^o (J/Mol K)

C₃H₈ = 269.9

O₂ = 205

CO₂ = 214

H₂O = 70

$∴ Δ r S = ( 3 × 214 + 4 × 70 − 1 × 269.9 − 5 × 205 ) \\ = -373 J/K$