UPSC Civil Services (Mains), Chemistry optional · 2024 · Paper I
Q3(a)(i). Viscosity of air at 298 K and at 0 K
Question
Calculate the coefficient of viscosity of air at temperatures: (I) 298 K and (II) 0 K. Assume that the collision cross-section (πσ²) of air is 0.28 nm² and the average molar mass of air is 29 g mol⁻¹.
Answer in brief
η = 1.89 × 10⁻⁵ kg m⁻¹ s⁻¹ at 298 K, and η = 0 at 0 K.
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Coversviscosity of gaseskinetic theory of gasescollision cross-sectionmean free pathmean speed
All parts of Question 3
- 3(a)(i) Viscosity of air at 298 K and at 0 K10 marks
- 3(a)(ii) Boyle temperature of Ar, CH₄ and C₆H₆5 marks
- 3(b)(i) Surface tension: ethanol or dimethyl ether5 marks
- 3(b)(ii) Pressure difference across a water droplet of radius 150 nm5 marks
- 3(c)(i) Change in Helmholtz energy on reversible isothermal compression10 marks
- 3(c)(ii) Why a tyre gets hot when it is pumped5 marks
- 3(c)(iii) Pressure of O₂ over NiO at 25 °C5 marks
- 3(c)(iv) Final temperature after Joule–Thomson expansion5 marks