Bio

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Lecture 37
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Bio

• Robert Boyle

Father of Modern Chemistry"
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Boyle

• was the first prominent scientist to perform
  controlled experiments and to publish his work
  with elaborate details
• He assembled what we would today call a
  "research group"

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• described experiments using a new vacuum pump
• bell jar and sound of bell
• mouse in jar
• pressure - volume inverse relationship

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He was a shy man with deep religiousconvictions.
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Go over homework
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We talked about the kinetic molecular theory that
explained the properties of gas pressure

• Ke ½ MV2

Where Mass is the number of atoms more particles
more pressure Velocity is the temperature more
temperature more pressure
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We Imagined a sheet being levitated by tennis
balls
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Increase the temperature

• Increase the kinetic energy

Increase the pressure
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Heat balloon over hot water
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So how do we measure Gas pressure
Pressure gauge

• Movement of a 1)needle 2)marker as a spring or
  3)material deforms

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monometer
We use kpa

• The gas pushes against a spring or gas that
  indicates the pressure in the vessel

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Open Monometer
Teeter totter
Instead of a spring or enclosed gas the open
manometer uses the weight of the air around us as
the apposing force
When the fluid is level then the gas inside
equals air pressure
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As we said last lecture,ambient air pressure
pushes against vapor pressure

• If
• ambient pressure vapor pressure
• Then Boiling of liquid

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What is ambient air pressure and what does it
consist of.

• Ambient air pressure is also called atmospheric
  air pressure
• 101 kpa

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So how much does the atmosphere over your head
weigh
The top of your head is 25 square inches and 14.7
pound per square inch so the air weighs 367.5
pounds
Guess how much 1 cubic meter of air weighs
1.3 kg
The air in your kid sisters room weighs more
than your kid sister
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Can a fish feel the water pressure all around it
If it weighs that much why cans we feel the
pressure
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atmospheric pressure
The weight of the atmosphere
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Barometer
Torricelli

• Air pressure compresses the mercury the same way
  my hand compressed the water balloon sending it
  upward
• The air pressure is fighting against gravity
  pulling down on the mercury

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Units on pressure
Write these numbers down
Pascals Millimeters of mercury Torr

• 1 atm 101 k pascals
• 1 atm 760 mm mercury
• 1 torr 1 mm mercury
• 1 atm 760 torr

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less
Less dense makes balloon lighter than air
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when you cool a gas it gets becomes less
voluminous and more dense
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Drinking bird
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So the kinetic molecular theory describes how the
pressure applied by a gas is dependent on the
atoms or molecule's kinetic energy.
It all makes sense if we assume a 4 things
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assumptions when dealing with the
kinetic-molecular theory of gases

• the walls of the container are perfectly elastic
  losing no energy in the collision
• 2) Gas particles are in straight line motion
• 3) the molecules take up relatively no space
• 4) there are no forces of attraction or repulsion
  between molecules
• 5) The Kinetic energy of the particles increase
  with temperature

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In an open container the pressure inside is only
as great as the atmospheric pressure
If the pressure inside is grater then high energy
atoms leave until pressure equality
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In a closed system the pressure increases because
the walls of the container contain the force of
the gas
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Do the can demo
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How does a Vacuum work
Creating a Pressure imbalance
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We discussed the fact that air pressure is all
around us

• air pressure is a combination of the weight of
  Oxygen, nitrogen, Carbon dioxide, water

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Atmospheric pressure is the pressure from
everything in the air

• O2 CO2 Smog

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The pressure exerted by a trapped gas is both
the pressure of the gas and the water vapor
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When calculating the pressure of a system you
must take all these pressures into account. 
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There are vapor pressure tables that tell what
pressure a given off by a particular amount of
water generates
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Partial pressures are like putting rocks in a
book bag. additive
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Dalton figured out that the pressure of a gas is
equal to the sum of all the little gasses that
make up the gas.

• Ptotal P1 P2 P3

Daltons law of Partial pressures
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If you cool something down really cold the atoms
come together and everything slows down
At what temperature does all matter stop
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Jacques Charles studied the relationship between
temp, volume, pressure.

• He was hoping there was a direct relationship and
  there was.

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Use bulb to generate graph
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But notice that the graph does not go through the
origin!!!

• At what temperature does the volume go to zero

Charles extended the graph and found that all
matter should have 0 volume at !!!!!!!
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Zero volume was at 273 degrees Centigrade
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Back in the 1650s there were two temperature
scales

• Fahrenheit
• based on freezing point of water
• Celsius
• based on freezing and boiling point of water

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So Charles set up a solid mathematical
relationship between volume and temperature he
had to move the y axis so when volume was 0
temperature was 0
He made a new temperature scale you run all gas
law problems on and wrote a equation
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To do this the y axis was moved 273 degrees from
the basis of Celsius and the new temperature was
called Kelvin

• Celsius 273 Kelvin K

The equation to predict vol from pressure is
called Charless Law
Dont memorize this
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To use the simple math equations for pressure
volume and temp you must use the Kelvin
temperature Scale where Kelvin equals to
Celsius 273 then
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So if we know the volume is 50cm3 at 200 Ko
degrees then what is the volume at 400 degrees
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Example 1What temp is need to change 30ml of a
gas at 14oC to 22ml

• Example 2
• What temp is need to change
• 1 ml of a gas at 20oC to 3ml of a gas