(1) The value of entropy change, Sβ – Sα (in J mol^–1 K^–1), at 300 K is ____.

Question

The entropy versus temperature plot for phases α and β at 1 bar pressure is given.

S_T and S₀ are entropies of the phases at temperatures T and 0 K, respectively.

The transition temperature for α to β phase change is 600 K and C_p,β – C_p,α = 1 J mol^–1 K^–1. Assume (C_p,β – C_p,α) is independent of temperature in the range of 200 to 700 K. C_p,α and C_p,β are heat capacities of α and β phases, respectively.

(1) The value of entropy change, S_β – S_α (in J mol^–1 K^–1), at 300 K is ____.

[Use: In 2 = 0.69

Given: S_β – S_α = 0 at 0 K]

(2) The value of enthalpy change, H_β – H_α (in J mol^–1), at 300 K is _____.

Answer 1

(1)

(2) ∆H₆₀₀ – ∆H₃₀₀ = 1 × (C_p,β – C_p,α) (600 – 300)

Now, at transition temperature,

∆H₆₀₀ = T∆S₆₀₀

= 600 × (6 – 5) 

= 600 J mol^–1

600 – ∆H₃₀₀ = 1 × 1 × 300

∆H₃₀₀ = 600 – 300

= 300 J mol^–1