Question 12 of 23 Three liquid samples of known masses are heated to their boili

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Question 12 of 23 Three liquid samples of known masses are heated to their boiling points with the use of a heater rated at Map 425.0 W. Once the boiling points of each sample are reached, the samples are heated for an additional 5.80 min, which results in the vaporization of some of each sample. After 5.80 min, the samples are cooled and the masses of the remaining liquids are determined. The process is performed at constant pressure. The results are recorded in the table below Boilin Liquid Initial Mass Final Mass Point (OC) (g) (g) 323.49 482.69 C2H5OH 78.3 485.09 36.1 83.93 C5H12 312.05 80.1 653.86 Calculate the molar enthalpy of vaporization, AH and the molar entropy of vaporization, ASvap, for each vap sample. Assume that all of the heat from the heater goes into the sample. Liquid Vap Number Number J mol K kJ mol C2H50H Number Number Scroll down to J. mol- K C5H kJ mol view the second part of this problem Number Number mol kJ mol CGH 16 Previous 3 Give Up & View Solution Check Answer Next Exit Hint

Explanation / Answer

Initial mass of C2H5OH= 482.69 gm , mass of remaining liquid = 323.49 gm, mass of C2H5OH vaporized = 482.69-323.49 =159.2 gm. Moles of C2H5OH= mass/molar mass = 159.2/46= 3.46 moles. This is possible only due to supply of heat 425W for 5.8 seconds.hence heat supplied = 425* J/sec*5*60 joules = 127500 Joules=127500/1000Kj=127.5KJ

Hence latent heat of vaporization = 127.5/3.46 KJ/mole=36.85 Kj/mole

Entropy of vaporization = latent heat/Boiling point in K= 36.85/(78.3+273) KJ/mole.K= 0.1048 KJ/mole.K=104.8 J/mole.K

2. for C5H12, moles of evaporated = (485.09-83.93)/72 =5.57 moles.

Latent heat of vaporization = 127.5/5.57= 22.89 KJ/mole and entorpy of vaporization = 22.89/(36.1+273)= 0.074 Kj/Mole.K=0.074*1000=74 J/mole.K

3. for C6H12, moles evaporated= (653.86-312.05)/78 =4.382 moles. Latent heat of vaporization = 127.5/4.382 =29.09 Kj/mole and entropy of vaporization= 29.09/(80.1273)= 0.082 Kj/mole.K=82 J/mole.K

Entropy change is degree of disorder. Higher the higher the entropy, higher the disorder. Hence lowest entropy suggests highly ordered. Hence highly ordered to low ordered is C5H12, C6H12 and C2H5OH.

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