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271. The equation which perfectly represents Gibbs Phase Rule for a process where the pressure is also a variable is expressed as : (a) F = P – C + 2 (b) F = C + P – 1 (c) F = P – C – 1 (d) F = C – P + 2 BHEL ET 2019 . (d) : Gibbs phase rule- P + F = C + 2 or F C P 2 = − + P = Number of phase C = Number of chemical components n = number of non-compositional variable (i.e. n=2) h = 2 i.e., pressure and temperature F = Degree of freedom Answer 272. Which relationship defines Gibbs free energy G: (a) G = H + TS (b) G = H - TS (c) G = U + TS (d) F = U + TS SJVN ET 2013 APPSC AEE 2016 . (b) : Gibbs free energy 'G' G H TS = − Answer 273. Joule-Thomson coefficient is defined as : (a) h T P   ∂     ∂ (b) T H P   ∂     ∂ (c) P H T   ∂     ∂ (d) h P T   ∂     ∂ MPPSC AE 2016 BPSC AE Mains 2017 Paper - V : (a) Joule thomson co-efficient:- ...

81. The density of water is maximum at   (a) 20 ºC             (b) 4 ºC  (c) 0 ºC               (d) -4 ºC  UPPSC AE 12.04.2016 Paper-II  Ans : (b) The maximum density of water occurs at 4  ºC because, at this temperature two opposing effects are in balance. In ice, the water molecules are in a crystal lattice that has a lot of empty space. When the ice melts to liquid water, the structure collapses and the density of the liquid increases. Thus, the density of water is a maximum at 4 ºC                                 82. A perfect gas at 27 °C is heated at constant pressure so as to triple its volume. The final temperature of the gas will be.  (a) 81 °C           ...