Diffusion.pptxppppppppppppppppppppppppppp

Science
Unit:
Diffusion
Solutions

Keywords
random
Brownian motion
medium
diffusion
fluid

Keywords
Something that happens without a clear pattern, making it
unpredictable, is described as random.
Brownian motion is the random movement of particles in a fluid, due to their
collision with particles in the surrounding medium.
A medium is usually a liquid or gas that other substances can mix into or
move through, enabling other substances to mix or interact.
Diffusion is the movement of particles from an area where there are lots, until
there is a random distribution of particles throughout a medium.
A fluid is a substance that flows or takes the shape of its container. Liquids
and gases can be described as fluids.

Lesson outline
Brownian motion
Diffusion
Diffusion
Factors affecting the speed of diffusion

Explanation
Ideas in science have their origins in observations.
Brownian motion
During the 18th century technology improved, and
the use of microscopes became a popular way of
making observations.
Robert Brown was a Scottish botanist
at the turn of the 19th century; he
studied plants using microscopes.
18th century
microscope
Right: M0000212: Nachet collection: Dellebarre microscope, Wellcome Collection, licensed under CC BY 4.0

Explanation
Brownian motion
In 1827, under a microscope, Brown observed pollen grains
moving randomly in water.
Brown’s initial thought was the
movements were because the
pollen grains were alive.

Explanation
To test his hypothesis, Brown observed other tiny
substances, like fine dust and soot particles, under his
microscope.
Brownian motion
Brown noticed these other particles moved
about in a similarly random way but struggled
to explain why.
It wasn’t until the early 20th century that work by various other
scientists confirmed and explained what Brown had observed.

Explanation
Today, the random movements Robert Brown first
observed is known as Brownian motion.
Brownian motion
Brownian motion is the random movement of
particles in a fluid (i.e., a liquid or gas), due to
their collision with particles in the surrounding
medium.
The yellow spot tracks the movement of just one
particle as it collides with the other black particles.
Brownian motion large.gif, Francisco Esquembre, Fu-Kwun and lookang, 2012, licensed under CC BY 3.0 SG

Explanation
Brownian motion
The medium is a fluid (i.e., gas or liquid material) that other
substances can mix into or move through.
medium
(water)
random movement
of another fluid

Explanation
Brownian motion
The key to Brownian motion is that the particles of one
fluid randomly collide with particles of the medium.
This results in the
unpredictable
movement of the
particles in both fluids.
larger blue dots = medium; smaller red dots = another fluid
Simulation by PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 (https://phet.colorado.edu)

True False
Justify your answer
True or false?
T F
Check
a
b
Particles’ movement is not impacted by the movement of
other particles.
Brownian motion is the orderly movement of fluid particles.
Particles can collide, pushing other particles onto a new,
random path.
Brownian motion

Task A
Practice
Brownian colliding random smoke
Brownian motion
Laura attended the theatre at the weekend. She’s
wondering why the smoke seemed to dance around the stage when
there was no wind.
Use the words in the box to complete the explanation
below.
The smoke particles are __________ with air particles
above the stage.
When the and air particles collide, both are
pushed into , unpredictable directions.
This action is known as motion.

Task A
Feedback
Brownian motion
Laura attended the theatre at the weekend. She’s
wondering why the smoke seemed to dance around the stage when
there was no wind.
Use the words in the box to complete the explanation
below.
Brownian colliding random smoke
The smoke particles are colliding with air particles
above the stage.
When the smoke and air particles collide, both are
pushed into random, unpredictable directions.
This action is known as Brownian motion.

Explanation
Brownian motion helps us to understand common
experiences.
Diffusion
smelling flowers
All these experiences occur because of diffusion.
watching water
change colour
smelling freshly
baked bread

Explanation
Diffusion is the process of particles spreading out in a
medium, moving from an area where there are lots of particles
until they are randomly distributed throughout the medium.
Diffusion
● blue dots (start on the left) = particles causing
baking bread smell
● red dots (start on the right) = air particles
For example, smells are noticed when gas particles reach the nose.
Middle: Simulation by PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 (https://phet.colorado.edu)

Explanation
Fluid particles are able to diffuse because they are constantly
moving and colliding with each other and the medium’s particles.
Diffusion
The collisions between particles pushes them in random, new directions.
● blue dots (start on the left) = particles
causing incense smell
● red dots (start on the right) = air particles

Explanation
Diffusion
Diffusion by Brownian motion also occurs in liquids.

Check
a
b
c
Diffusion
dissolving
diffusion
Brownian motion
What name is given to the process of particles spreading out, moving from
an area where there are lots of them until they are randomly spread
throughout a medium?

Practice
Task B
On his way to his history lesson, Lucas could smell cupcakes. The
food technology room is at the other end of the corridor from the
history classroom.
Diffusion
The particles spread throughout the
air in the corridor (via Brownian
motion), to where….
There are many particles
causing the cupcake smell
in the food tech room.
This process is known
as diffusion.
As the food tech
door opens, they
collide with air
particles in the
corridor.
…there are fewer particles
causing the cupcake smell.
Put Lucas’ thoughts into a sensible order to explain why he can
smell the cupcakes.

Task B
Feedback
On his way to his history lesson, Lucas could smell cupcakes.
The food technology room is at the other end of the corridor
from the history classroom.
Put Lucas’ thoughts into a sensible order to explain why he can
smell the cupcakes.
Diffusion
There are many particles causing the cupcake smell in the
food tech room.
As the food tech door opens, they collide with air particles
in the corridor.
The particles spread throughout the air in the corridor (via Brownian
motion) to where there are fewer particles causing the cupcake smell.
This process is known as diffusion.

Explanation
Some factors affect the speed at which particles
undergo diffusion:
● the number of particles
● the amount of energy the particles have
(affected by the temperature of the substances)
● the size of the particles
These factors relate to the particles of both the medium and
the diffusing fluid.

Explanation
Recall that diffusion depends upon collisions that occur
randomly via Brownian motion.
more particles = more collisions
fewer particles = fewer collisions
Simulations by PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 (https://phet.colorado.edu)

Explanation
More particles colliding means diffusion can occur faster,
but only to a point…
…too many particles can slow
diffusion

Explanation
Smaller particles diffuse quickly because they are lightweight.
smaller particles = faster diffusion
Larger particles require collisions with more energy to move at speed.
larger particles = slower diffusion

Explanation
An increase in temperature means particles have more
energy. As such, the particles move faster, colliding more
often and with more force. This results in faster diffusion.
colder particles = slower diffusion hotter particles = faster diffusion

True False
Justify your answer
True or false?
Check
a
b
T F
Having more particles involved in diffusion always speeds up the
process of diffusion.
More particles means there are fewer collisions, pushing
particles into new positions; therefore, diffusion is faster.
If too many particles are colliding, this can make it difficult
for particles to spread out (i.e., diffuse) quickly.

Check
In which temperature water will the tea diffuse fastest?
60°C 75°C 90°C

Practice
Task C
Sam’s bus passes a sewage treatment works on
the way to school. The smell from the facility is more
noticeable in June than it is in February. Explain why that is.

Task C
Feedback
Sam’s bus passes a sewage treatment works on
the way to school. The smell from the facility is more noticeable
in June than it is in February. Explain why that is.
Your answer may include:
● The temperature is warmer in June than in
February.
The smell is more
noticeable in June
because…
● At higher temperatures, particles have
more energy and can collide more often.
● This means that the diffusion of particles
causing the sewage smell happens faster
when the temperature is higher (i.e. in
June).

Summary
● Particles released into a fluid (i.e., gas or liquid), move around
due to Brownian motion. This motion is caused by particles
randomly colliding into each other.
Diffusion
● Diffusion occurs via Brownian motion. It is the movement of
particles from an area where there are lots, until there is a
random distribution of particles throughout a medium.
● The speed of diffusion is affected by the number and size of the
particles colliding, and the energy the particles have when they
collide.

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