AL chem equilibrium (15)

(a)
NH4HS(s) = NH3(g) + H2S(g)
This is an heterogeneous equilibrium. The concentration/pressure of NH4HS solid should NOT be considered in the equilibrium expression.

KP' = PNH3•PH2S

For the decomposition of NH4­HS(s), equal amount of NH­3 and H2S is formed.
Hence, PNH3 = PH2S.

At 10oC:
T1 = (273 + 10) K = 283 K .. and .. K1 = (0.22 atm)2 = 0.0484 atm2

At 25oC:
T2 = (273 + 25) K = 298 K .. and .. K2 = (0.64 atm)2 = 0.4096 atm2

ln(K1/K2) = -(ΔH/R)(1/T1 - 1/T2)
ln(0.0484/0.4096) = -(ΔH/8.314)(1/283 - 1/298)

ΔH = +99830 J mol-1 = +99.83 kJ mol-1


(b)
(i)
H2(g) + CO2 = CO(g) + H2O(g)

(ii)
KP = PCO•PH2O/PH2•PCO2

For Experiment 1:
KP = (70)(46)/(23)(140) = 1

For Experiment 2:
KP = (80)(48)/(32)(120) = 1

For Experiment 3:
KP = (50)(80)/(40)(100) = 1

Average KP = (1 + 1 + 1)/3 = 1
KC = KP = 1

2009-07-19 19:00:20 補充：
第一題下半部更正如下：

At 10°C: T1= 283 K
P(NH3) + P(H2S) = 0.22 atm
Hence, P(NH3) = P(H2S) = 0.11 atm
K1 = P(NH3)•P(H2S) = (0.11)^2 atm^2 = 0.0121 atm^2

At 25°C: T2= 298 K
P(NH3) + P(H2S) = 0.64 atm
Hence, P(NH3) = P(H2S) = 0.32 atm
K2 = P(NH3)•P(H2S) = (0.32)^2 atm^2 = 0.1024 atm^2

2009-07-19 19:00:34 補充：
ln(K1/K2) = -(ΔH/R)(1/T1 - 1/T2)
ln(0.0121/0.1024) = -(ΔH/8.314)(1/283 - 1/298)

ΔH = +99830 J mol^1 = +99.83 kJ mol^1

回版主: 首先.氣體分子mole並非1:1:1, 而是0:1:1
因為NH4HS(s)係solid唔計入eqm eqt

至於2次方既問題, 我同樓上既諗法有d唔同
因為無論任何時候,
NH3(g) 同 H2S(g) 的 partial pressure應該相同
(因為mole數相等)
而 total pressure是兩氣體pressure相加
因此, 各氣體pressure應為total pressure的一半.

然後 K1=P(NH3) X P(H2S)
=(0.22/2)(0.22/2)
而非樓上所說的(0.22)^2
之後求出K1/K2的比例, 再代入公式即成.

完整解答:

(a)
Eqm Equation:

Kp=P(NH3)xP(H2S)

at 10 C,
P(NH3)=P(H2S)=(0.22)/2=0.11
K1=(0.11)^2=0.0121 atm^2

at 25 C,
P(NH3)=P(H2S)=(0.64)/2=0.32
K1=(0.32)^2=0.1024 atm^2

K2/K1=8.463

ln(K2/K1)=-(deltaH)/Rx(1/T2-1/T1)
ln(8.463)=-(deltaH)/(8.314)x(1/298-1/283)
deltaH=+99.83kJ/mol

(b)(i)
H2+CO2 <=> CO2+H2O

(ii)
From Expt 1, Kp=(23)(140)/((70)(46))=1
From Expt 2, Kp=(32)(120)/((80)(48))=1
From Expt 3, Kp=(40)(100)/((100)(80))=1
All three Expts agree that Kp=1

在NH4HS(s) = NH3(g) + H2S(g)
的氣體分子mole 是 1 : 1: 1
為何K1 和 K2要用2次方?
K1 = (0.22 atm)2 K2 = (0.64 atm)2

2009-07-20 22:46:29 補充：
第一位回答者在補充答案內更正了答案，
補充後的答案, 概念上正確.

第二位回答者在的答案, 概念上也正確.
但(b)(i)是錯的
因為題目有說明:
CO 要在product side