Phy-gases - Ans.fyi 參考答案

Phy-gases

Larry

2010-12-31 6:45 am

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Two contains A and B with volumes 100cm^3 and 400cm^3 respectively are shown. The tap X connecting the two containers is closed initially. Container A contains oxygen at a pressure of 4x10^5 Pa while there is a vacuum in container B. The temperature of both containers is maintained at 25度

(a) Find
(i) the number of moles of oxygen in container A, and
(ii) the root-mean-square speed of the oxygen molecules in A.

(b) Tap X is open and container B is heated to 100度, find
(i) the pressure in both containers, and
(ii) the number of moles of oxygen in container B.

回答 (1)

用戶25975

2010-12-31 5:00 pm

✔ 最佳答案

a i) Using PV = nRT, we have:

n = PV/(RT) = 4 x 105 x 100 x 10-6/(8.314 x 298) = 0.0161

ii) Mean k.e. of oxygen molecules = 3kT/2 = 3 x 1.38 x 10-23 x 298/2

= 6.6186 x 10-21 J

Mass of each oxygen molecule = 0.032/(6.02 x 1023) = 5.316 x 10-26 g

So:

0.5 x 5.316 x 10-26 x v2 = 6.6186 x 10-21

v = 482 m/s

b i) After opening the tap, the pressure of both containers is common, implying:

PA = PB

298 x 8.314 x nA/(100 x 10-6) = 373 x 8.314 x nB/(400 x 10-6)

1192nA = 373nB

nA = 0.313nB

Using the result from (a i):

nA + nB = 0.161

0.313nB + nB = 0.161

nB = 0.123

So the common pressure is 373 x 8.314 x 0.123/(400 x 10-6) = 95335 Pa

ii) See (b i)

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