Grahams Law Thomas Graham studied the effusion and diffusion of
gases. Diffusion is the mixing of gases through each other.
Effusion is the process whereby the molecules of a gas escape from
its container through a tiny hole Thomas Graham studied the
effusion and diffusion of gases. Diffusion is the mixing of gases
through each other. Effusion is the process whereby the molecules
of a gas escape from its container through a tiny hole
Slide 4
Spreading of gas molecules throughout a container until evenly
distributed. Passing of gas molecules through a tiny opening in a
container
Slide 5
Grahams Law states that the rates of effusion and diffusion of
gases at the same temperature and pressure is dependent on the size
of the molecule. The bigger the molecule the slower it moves the
slower it mixes and escapes. Grahams Law states that the rates of
effusion and diffusion of gases at the same temperature and
pressure is dependent on the size of the molecule. The bigger the
molecule the slower it moves the slower it mixes and escapes.
Grahams Law
Slide 6
Slide 7
KE = mv 2 Speed of diffusion/effusion Kinetic energy is
determined by the temperature of the gas. At the same temp &
KE, heavier molecules move more slowly. Larger m smaller v
Slide 8
Consider two gases at same temp. Gas 1: KE 1 = m 1 v 1 2 Gas 2:
KE 2 = m 2 v 2 2 Since temp. is same, then KE 1 = KE 2 m 1 v 1 2 =
m 2 v 2 2 m 1 v 1 2 = m 2 v 2 2 Divide both sides by m 1 v 2 2 Take
square root of both sides to get Grahams Law:
Slide 9
Grahams Law Rate of diffusion of a gas is inversely related to
the square root of its molar mass. The equation shows the ratio of
Gas As speed to Gas Bs speed.
Slide 10
This shows that the velocities of two different gases are
inversely proportional to the square roots of their molar masses.
This can be expanded to deal with rates of diffusion or effusion Or
deal with Molar mass, masses or Density This shows that the
velocities of two different gases are inversely proportional to the
square roots of their molar masses. This can be expanded to deal
with rates of diffusion or effusion Or deal with Molar mass, masses
or Density vAvA vAvA vBvB vBvB = = MBMB MBMB MAMA MAMA
Slide 11
Determine the relative rate of diffusion for krypton and
bromine. Kr diffuses 1.381 times faster than Br 2. Grahams Law The
first gas is Gas A and the second gas is Gas B. Relative rate mean
find the ratio v A /v B . Kr 83.80 36 Br 79.904 35
Slide 12
A molecule of oxygen gas has an average speed of 12.3 m/s at a
given temp and pressure. What is the average speed of hydrogen
molecules at the same conditions? Grahams Law Put the gas with the
unknown speed as Gas A. O 15.9994 8 H 1.00794 1
Slide 13
If equal amounts of helium and argon are placed in a porous
container and allowed to escape, which gas will escape faster and
how much faster? Grahams Law Example problem Rate of effusion of A
= = Rate of effusion of B MBMB MBMB MAMA MAMA
Slide 14
Grahams Law Example Calc. Rate of effusion of He = = Rate of
effusion of Ar 40 g 4 g Helium is 3.16 times faster than
Argon.
Slide 15
Grahams Law Lab of Diffusion HCl NH 3 50 cm NH 4 Cl(s) Choice
1: Both gases move at the same speed and meet exactly in the
middle.
Slide 16
Diffusion HCl NH 3 X cm (Grahams Law Ratio) X cm NH 4 Cl(s)
Choice 2: Lighter gas moves faster; meet closer to heavier
gas.