Lesson 33 questions - Kinetic theory and Pressure
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1. (a)
What do you see when looking at Brownian motion in air?
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(b)
What changes do you see if the air is heated?
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2. Define pressure and give its units.
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3. List six assumptions that you have to make about molecules when deriving the
equation for the kinetic theory of gases.
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4. (a)
A molecule of mass 3x10-26 kg moving at 4x102 ms-1 collides
elastically with a wall. What is the change of momentum of the molecule?
Change in momentum = …………………. Unit………… (3)
(b)
How long would it take this molecule to travel a distance of 0.4 m?
Time = …………….. s (2)
MOST
5.
(a)
What is meant by the root mean square speed of gas molecules?
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(b)
What is the difference between the root mean square of a group of
gas molecules and their average speed?
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6.
of 105 Pa:
Calculate the root mean square speeds for the following gases at a pressure
(a)
(b)
(c)
(d)
(e)
air
carbon dioxide
density 1.29 kgm-3
root mean square speed = …………….. ms-1 (2)
density 1.98 kgm-3
nitrogen
root mean square speed = …………….. ms-1 (2)
density 1.25 kgm-3
chlorine
root mean square speed = …………….. ms-1 (2)
density 3.21 kgm-3
hydrogen
root mean square speed = …………….. ms-1 (2)
density 0.09 kgm-3
root mean square speed = …………….. ms-1 (2)
7.
Calculate the pressure of three samples of air of density 1.29 kgm-3 with
different root mean square speeds:
(a) 4.0x102 ms-1
pressure = ……………..Pa (2)
(b) 5.0x102 ms-1
pressure = ……………..Pa (2)
2
(c) 6.0x10 ms
-1
pressure = ……………..Pa (2)
9.
A sample of gas of volume 0.1 m3 and at a pressure of 2.0x105 Pa is
enclosed in a cylinder. If the root mean square speed of the gas molecules is 5.5x102
ms-1 and the mass of each molecule is 3.5x10-26 kg calculate the number of gas
molecules in the cylinder.
Number of gas molecules = ……………… (3)
10.
A sample of gas at a pressure of 1.5x105 Pa is contained in a cylinder with a
volume of 0.05 m3. If there are 1.2x1025 molecules of gas in the cylinder with a root
mean square speed of 350 ms-1 calculate the mass of one gas molecule.
Mass of one gas molecule = ………………kg
(3)
SOME
11.
Suppose there are N molecules in a
rectangular box of dimensions a, b and l and
suppose that the molecule has a velocity v with
the components as shown.
vy
b
a)
What is the change in velocity
of the particle when it hits the shaded face if
the collision is totally elastic?
vx
vz
a
(1)
L
b)
i)
What is the time interval before the same molecule makes a 2nd
collision at the same face?
(1)
ii)
An therefore what is the frequency of collisions?
(1)
c)
From the definition of Pressure and by finding the rate of change of
momentum for one molecule show that for N molecules:
P  Nmv2 / 3V .
(6)