122ch11b - 31 11.47) 11.49) The question refers to Fig...

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Unformatted text preview: 31 11.47) 11.49) The question refers to Fig 11.24 (could also use 11.25, lnP vs. 1/T since it is for ethyl alcohol, i.e. ethanol). The boiling point is the temperature at which the VP of the liquid equals the prevailing atmospheric (barometric) pressure. Barometric pressure varies from day to day and depends on location so the b.p. of a substance can vary. a) The b.p. of ethanol at 200 torr is - 48C. b) The VP of ethanol at 60C is - 350 torr. Thus, when the barometric (external) pressure is - 350 torr ethanol will boil at 60C. c) The b.p. of diethyl ether at 400 torr is - 18C. d) The VP of diethyl ether at 40C is above the normal b.p. at 760 torr. From figure 11.24 the VP would be around 1000 torr at 40C. Thus, when the barometric (external) pressure is - 1000 torr diethyl ether will boil at 40C. 32 11.52) a) b) Also, see Fig 11.27(a). The triple point occurs at 4.58 torr. 33 11.53) See figure 11.27(a) in problem 11.52 above. At a temperature of -0.5C and a pressure of 0.005 atm water is in the vapor (gas) phase since this pressure is well below that of the triple point and the temperature is just below that of the triple point (and normal f.p. of 0C). As the pressure is increased, at a constant temp. of -0.5C, the water vapor would form a solid (deposit) at a pressure of around 4 torr. As the pressure is increased further, the solid would MELT to form liquid water. This occurs because the melting point curve (equilibrium between solid and liquid) leans to the left and the m.p. decreases with increasing external pressure . The fact that s ----> R when P inc. is very unusual. Whenever P inc. the system always goes to the phase with a smaller volume. For most substances the phase with the smaller volume is the solid ( solid is more dense than the liquid ) so the m.p. curve (s ----> R equilibrium line) leans to the right (positive slope) and as P inc. R----> s ( m.p. inc. with inc. pressure ). For H 2 O (and a very few other substances) the phase with the smaller volume is the liquid ( solid H 2 O , ice, is less dense than the liquid ). The m.p. curve (s ----> R equilibrium line) leans to the left (negative slope) and as P inc. s ----> (negative slope) and as P inc....
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This note was uploaded on 06/11/2011 for the course CHEM 122 taught by Professor Zellmer during the Spring '07 term at Ohio State.

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122ch11b - 31 11.47) 11.49) The question refers to Fig...

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