課程名稱︰普化丙
課程性質︰
課程教師︰鄭淑芬
開課系所︰機械系
考試時間︰2006年6月8日
試題 :
Problems:
17. Briefly explain the three laws of thermodynamics, and give one
representative equation for each of them: (9%)
18. A reference book lists the following values for gallium at 298k
_______________________________________________________________
Substance △Hf(kJ/mol) △Gf(kJ/mol) S(J/mol K)
_______________________________________________________________
Ga(s) 0 0 x
Ga(l) 5.578 0.0888 59.25
Ga(g) 271.96 233.76 169.03
_______________________________________________________________
(a) Estimate the normal boiling point of gallium (4%)
(b) Gallium metal has a melting point of 29.8。C.
Estimate the S value of Ga(s) (4%)
19. The equilibrium constant for
NH4HS(s)←→NH3(g) + H2S(g)
at 25。C is Kc=1.6x10^-4
(a) What is the Kp value at this temperature? (4%)
(b) When solid NH4HS and 0.450 mol of gaseous NH3 were placed into a 2.0L
vessel at 25。C, what are the partial pressures of NH3 and H2S at
equilibrium? (4%)
(c) The van't Hoff equation shows the relationship between the equilibrium
constant and the absolute temperature:
ln(K1/K2) = -(△Hvap/R)(1/T1 - 1/T2)
Knowing that Kc is 2.96x10^-4 at 40。C , estimate the enthapy of this
reaction. (3%)
20. Consider an aqueous solution that contains 0.015M in Cd2+ ion and 0.020M
in Zn2+ ion. In order to seperate them by precipitating one of them as
sulfide without precipitating the other, what should be the pH value of
the saturated H2S ([H2S]=0.10M) solution? Show your calculation to
justify your answer.
(Ksp of CdS = 3.6x10^-29) (Ksp of ZnS = 1.1x10^-21)
(Ka1 and Ka2 of H2S = 1.1x10^-7 and 1.1x10^-19, respectively) (10%)
21. The decompositon of dimethy1 ehter at 504。C is a first-order reaction
with a half-life of 27.2 min.
(CH3)2O(g) → CH4(g0 + H2(g) + CO(g)
(a) What will be the partial pressure of (CH3)2O(g) after 1.50h if its initial
pressure was 650mmHg? (5%)
(b) What will be the total gas pressure after 1.50h ? (2%)
22. The following mechanism has been proposed for the reaction for the
reaction chlorine and dichloromethane, CH2Cl2:
Step 1. Cl2←→2Cl (forward and its reverse both fast)
Step 2. CH2Cl2 + Cl → CHCl2 + HCl (slow)
Step 3. CHCl2 + Cl → CHCl3 (fast)
(a) What is the overall reaction equation ? (2%)
(b) Indicate the intermediate species. (2%)
(c) Write the rate law implied by this mechnism, and show your assumption. (6%)
23. Consider the titration of 25.0mL of 0.100 M CH3COOH with 0.100M NaOH
solution (Ka of CH3COOH = 1.80x10^-5)
(a) Calculate the pH values after the following volumes of NaOH have been
added: 0mL ; 5mL; 10mL before the equivalence point ;
at equivalence point; 5.0mL after the equivalence point;
and 10mL after the equivalent point. (18%)
(b) Draw the titration curve (4%)
(c) What is the pKa range of the indicator which will be needed? (2%)
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