Q4(a). Triple point, stable phase and enthalpy of sublimation of a new drug
A new drug has been synthesized and its phase diagram is explored. It is found that near its triple point, the vapour pressure over the liquid (Pₗ) and over the solid (Pₛ) are given by: ln Pₗ = −3010/T + 13.2 and ln Pₛ = −3820/T + 16.1. Calculate the triple point temperature and pressure. Is the new drug solid, gas or liquid at 1 bar, 298 K? What is ΔHsublimation? Explain.
Answer in brief
Triple point: 279.3 K and 11.3 bar; at 1 bar and 298 K the drug is a gas; ΔHsub = 3820R = 31.8 kJ mol⁻¹.
Part of VKC Basic
Read the key points and the full model answer with VKC Basic
VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coverstriple pointphase diagramClausius–Clapeyron equationenthalpy of sublimationvapour pressure
All parts of Question 4
- 4(a) Triple point, stable phase and enthalpy of sublimation of a new drug15 marks
- 4(b)(i) Polarography and concentration polarisation15 marks
- 4(b)(ii) Concentration cells; fuel cells as energy converters5 marks
- 4(c)(i) Time of maximum concentration of B in A → B → C10 marks
- 4(c)(ii) Yield of P₁ from three parallel paths5 marks