有關化學平衝常數的問題

The answer is : (B) (1/7)p

The key point of this question is that :
The system is under "constant pressure p" and "constanttemperature", both initially and at equilibrium.

X(g) ⇌ Y(g) + Z(g)

At eqm :
PX = (1/7)p
PY = PZ = [p - (1/7)p]/2 = (3/7)p

Hence, KP
= PY•PZ / PX
= [(3/7)p]² / (1/7)p
= (9/7)p

2012-05-18 09:15:54 補充：
題目重點是 constant pressure （定壓）。

可能你和 male mature 的計算都用了 constant volume （定體積），仗 pressure 改變，於是

Total pressure at eqm = (1/7)p + (6/7)p + (6/7)p = (13/7)p ≠ initial pressure

2012-05-18 09:17:19 補充：
發問時點數改扣除，得到答案後刪除問題只會選人不利已。

A gas X dissociates on heating to set up the following equilibrium:
X(g) Y(g) + Z(g)
A quantity of X was heated at constant pressure, p, at a certain temperature. The equilibrium partial
pressure of X was found to be 1/7 p. What is the equilibrium constant, Kp at this temperature?
A 6/7 p
B 9/7 p
C 36/7 p
D 6 p
E 9 p
Sol:X(g) →Y(g) + Z(g)反應前: P
反應後: P/7 6P/7 6P/7Kp=[Y(g)]*[Z(g)/[X(g)] =(6P/7)*(6P/7)/(P/7) =36P/7 你的答案是正確的(Kp=36P/7)
B是錯誤的答案