Part A CaO can be used as a drying agent. One such application occurs when water
ID: 512110 • Letter: P
Question
Part A CaO can be used as a drying agent. One such application occurs when water is added to dry concrete or cement. The reaction that occurs is CaO(s)+H2O(l)Ca(OH)2(s) The product is commonly called slaked lime. Assuming the commonly used standard-state temperature of 25C, calculate Suniv for this reaction using table from the table below. Substance S [J/(Kmol)] Hf (kJ/mol) CaO(s) 39.9 635.1 H2O(l) 69.9 285.8 Ca(OH)2(s) 83.4 986.1 Express your answer to three significant figures and include the appropriate units. Part B A particular solvent with Svap=112.9J/(Kmol) and Hvap=38.0kJ/mol is being considered for an experiment. In the experiment, which is to be run at 75 C, the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not? The solvent would A particular solvent with and is being considered for an experiment. In the experiment, which is to be run at 75 , the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not?1 be suitable because Suniv>0. 2 not be suitable because Suniv>0. 3 be suitable because Suniv<0. 4 not be suitable because Suniv<0.
Explanation / Answer
Express your answer to three significant figures and include the appropriate units
Substance.....S in J/(K*mol)......Delta H f in kJ/mol
CaO (s).......39.9.................... -635.1
H2O(l).........69.9...................... -285.8
Ca(OH)2(s)..83.4.................... -986.1
CaO(s) + H2O(l) <-->Ca(OH)2(s)
Tsurr = 0 deg. C = 273 K
S_surr = -H/Tsurr = : -(-986.1 - 635.1 - 285.8)/298 = 218.8
S_surr = 218.8 J/K
S_total = 218.8 - 26.4
S_total = 192.4 J/K =
particular solvent with Delta S* vap = 112.9 J/(K * mol) and Delta H* vap = 38.0 kJ/mol is being considered for an experiment. In the experiment, which is to be run at 75 C, the solvent must not boil. Based on the overall entropy change associated with the vaporization reaction, would this solvent be suitable and why or why not?
The Solvent Would :
be suitable because S univ>0 .
not be suitable because S univ>0 .-answer
be suitable because S univ<0 .
not be suitable because S univ<0 .
Suniverse=Ssystem+Ssurroundings
Suniverse=Ssystem H system/T
Suniverse=112.9 JK mol 38.0kJ/mol/ (75+273)×1000J1kJ
Suniverse=112.9 J/K mol109.19J/K mol
=3.71 JK mol
bp = Hvap / Svap = (38000 J / mole) / (112.0 kJ/ moleK) = 337 K = 64C solvent would boil and would therefore NOT be suitable b/c Stotal > 0
be suitable because S univ>0 .
not be suitable because S univ>0 .-answer
be suitable because S univ<0 .
not be suitable because S univ<0 .
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