Pressure

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Pressure

• Chemistry Modeling 2013

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Pressure Macro-Scale

• Pressure is the amount of force exerted over a
  given area
• The force exerted is caused by particles
  collisions with the surface of a container is a
  PRESSURE EVENT
• Familiar unit is pounds per square inch or psi
  (tire pressure)
• This is how many pounds of force something pushes
  on every 1 square inch of surface contact it has
  with an object
• Changes and effects of Pressure are only
• observed in gases (not liquids or solids)

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Atmospheric Pressure

• Atmospheric pressure is the amount of pressure
  exerted on an object by all the particles in the
  atmosphere directly above that object
• Remember that air is made of particles, which
  have mass. That massive amount of atmosphere is
  pushing down on you at all times
• What affects atmospheric pressure?
• Elevation
• Temperature
• Amount of particles in the gas (water,
  particulate)

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Measuring Pressure

• Units
• Pounds per square inch (psi)
• Kilopascals (kPa)
• Atmospheres (atm)
• Millimeters of mercury (mmHg)

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Measuring Pressure

• Kilopascals
• The standard metric unit for measuring pressure.
• 101.3 kPa is pressure at sea level at 0C
• Atmospheres
• A convenient unit where the pressure at 0C at
  sea level is equal to 1.00 atm.
• mmHg
• A unit based on the amount of liquid mercury that
  can be pushed up a tall column by atmospheric
  pressure.
• 760 mmHg is pressure at sea level at 0C
• Pounds per square inch (psi)
• The unit of pressure used my many industries in
  the US
• 14.7 psi is the pressure at sea level at 0C

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What does this mean?

• 760 mmHg 101.3 kPa 1 atm 14.7 psi
• For every 1 atmosphere there is 760 mmHg
• What are some other for every statements you
  could write?

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How to convert between pressure units

• 3.10 atm ? kPa
• Use equalities to solve.
• What do you know?
• Given 3.10 atm
• What equalities can you use?
• 1 atm 101.3 kPa
• Set up ratios, cross multiply solve
• 3.10 atm 1 atm
• x 101.3 kPa
• (cross multiply to solve for x)
• The answer is 314 kPa

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How to convert between pressure units

• 712 mmHg ? psi
• Use equalities to solve.
• What do you know?
• Given 712 mmHg
• What equalities can you use?
• 760 mmHg 14.7 psi
• Set up ratios, cross multiply solve
• 712 mmHg 760 mmHg
• x 14.7 psi
• (cross multiply to solve for x)
• 760 x (712 14.7) or 760 x 10500
• The answer is 13.8 psi

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STP

• Standard Temperature and Pressure
• a standard set of conditions for experimental
  measurements established to allow comparisons to
  be made between different sets of data.
• Temperature 273 K (0 Celsius, 32 Fahrenheit)
• Pressure 1 atmosphere of pressure (often
  expressed as at sea level)

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KMT The Kinetic Molecular Theory

• Particles of a gas are in Constant Motion, moving
  Randomly until they Collide with another particle
  or a container wall.
• Particles experience Elastic collisions.
• The Speed of the particles is directly related to
  the Temperature
• Pressure of a gas is related to the Number and
  the Strength of the collisions with the sides of
  the container wall.