(a) With the aid of a plot, explain what a Phase diagram is for a single pure su
ID: 700777 • Letter: #
Question
(a) With the aid of a plot, explain what a Phase diagram is for a single pure substance, outlining its main features. Explain the terms: (0 Superheated vapour and (ii) degrees of superheat. 8 Marks) (b) Assuming the validity of Raoult's law for the benzene (toluene (2) system, determine the corresponding gas and liquid mole fractions for both components (ie. for both benzene and toluene), given that the temperature of the system is T= 105°C and total pressure is P = 120 kPa. 7 Marks Note: (1) Antoine's equation is given by And the corresponding constants for benzene (1) and toluene(2) are: A; 13.78 , B,-2727 . C.-217.6 As = 13.93 . B, = 3057, G-217.6 (2) Raoult's law c Describe in your own words what a psychrometric chart is and what properties of moist air it helps us determine 5 Marks Consider a moisthumid air at 41°C and 10% relative humidity. Using the given psychrometric chart, determine:() wet bulb temperatures; (i) the devw point temperature and (ii) specific enthalpy of air 5 Marks)Explanation / Answer
Ans b
Temperature of the system T = 105°C
Calculate the saturation pressure P1* of benzene at T
ln P1* = 13.78-[2727/(105+217.6)] = 5.3268
P1* = 205.78 kPa
Calculate the saturation pressure P2* of toluene at T
ln P2* = 13.93-[3057/(105+217.6)] = 4.454
P2* = 85.97 kPa
From the Raoult’s law
P = P1* x1 + P2* (1-x1)
120 = 205.78 x1 + 85.97 - 85.97 x1
120 - 85.97 = 119.81 x1
34.03 = 119.81 x1
x1 = 0.284 = liquid mol fraction of benzene
x2 = 1 - 0.284 = 0.716 = liquid mol fraction of toluene
y1 P = x1 P1*
y1 = 0.284 x 205.78 / 120 = 0.487 = vapor mol fraction of benzene
y2 = 1-y1 = 1-0.487 = 0.513 = vapor mol fraction of toluene
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