Entropy

• It is the measure of randomness of the system or disorder of the system.
• More the disorder, more the entropy of the system

Types of Entropy Change

The change of one state of matter to another is called Phase Transition . Therefore, entropy change is of different types.

(1) Entropy of Fusion- The change in entropy when 1 mole of solid substance changes into its liquid state at its melting point is known as entropy of fusion & it is represented by

Δs = (q/t)      Δfusion S = (q(fusion) / T) = (ΔH/T)

Q. Calculate the entropy of fusion of ice, its latent heat of fusion is 6 KJ/mol. At its melting point.

ΔS_fusion = (ΔH_f /T)

ΔS_fusion = 6000/273 = 21.97 JK^-1 mol^-1

(2) Entropy of Vaporization → The change in entropy when 1 mole of a liquid changes into its vapour at its boiling temp.

 ΔS_Vaporization = (ΔH_Vaporization / T)

Question. The enthalpy change for the transition of liquid water to steam. ΔH_Vap = 40.8 KJ/mol at 373 K .Calculate the entropy change associated with vaporization

ΔS_Vaporization = 40800/373

                                                    = 109.3 JK^-1 mol^-1

(3) Entropy of Sublimation → The change in entropy when 1mole of a solid changes into vapour at a particulate temp. is known as entropy of sublimation.

 ΔS_Sublimation = (ΔH_Sublimation / T)

Question. Predict in which of the following entropy Increases or decreases. What entropy measure.

1. A liquid crystallizes into solid → decreases

2. Temperature of crystalline solid is raised from or to 115K → increases

Because with increases in temp., Kinetic Energy Increases, thus randomness also increases.

3. 2NaHCO₃ → Na₂CO₃ + CO₂ (g) + H₂O → increases

4. H₂ (g) → 2H (g) → increases

5. H₂O (s) → H₂O (L) → increases

6. O₂ (g) + 2SO₂ (g) → 2SO₃ (g) decreases

7. 2H₂ (g) O₂ (g) → 2H₂O (L) decreases

8. NH₄CL (s) + aq → NH₄ (aq) + CL^- (aq) → increases