Part I: Hybridization and Multiple Bonds, Gases and Pressure

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Part I Hybridization and Multiple Bonds, Gases
and Pressure

• CHM 102
• Wednesday, June 27th

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Hybridization and Multiple Bonds

• With polyatomic molecules, sigma (s) bonds are
  the single bonds, and are formed by interactions
  between hybrid orbitals (i.e. sp, sp2).
• Pi (p) bonds form everything past the single
  bond, and are formed by interactions between the
  atomic orbitals (i.e. s, p, d, etc.) left over
  after hybridization.

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Hybridization Example Ethene

• How many s and p bonds are there in ethene?
• What is the hybridization on the carbons in
  ethene?
• How many p orbitals on each carbon form the p
  bond(s)?

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Ethenes Multiple Bond

• With sp2 hybridization on each C, but 3 available
  p orbitals originally, this means we have 1
  remaining p orbital on each C. This remaining p
  orbital on each C leans in and forms the p bond.

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How many sigma and pi bonds are present? What is
the hybridization of the circled nitrogen? How
many free p orbitals are on the circled carbon?
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Gases

• Gases have no definite shape and no definite
  volume.
• Gas takes the shape of its container.
• (Think about this does liquid?)
• Think about it Dry Ice Fog-why does it float
  as it does? Why did it put out the candle?
• Think about it Soda Bottle- Is it empty?

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Air

• What is in air?
• 78 ________________
• 21 ________________
• 0.9 ________________
• Other gases such as CO2 are present, but in
  smaller relative percentages.
• So that empty soda bottle wasnt really empty
  in the truest sense of the word!

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Redefining Empty Space

• While the soda bottle wasnt empty, only roughly
  0.1 of the soda bottle volume is taken up by
  molecules.
• Each gas molecule can essentially behave as if it
  was on its own, with no neighbors anywhere
  nearby.
• If you were a gas molecule, the next closest gas
  molecule would be over near Target or Hooters!

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Why do we care about gases?

• Zepplin video
• The point being not understanding the chemistry
  of gases can have deadly effects in many fields,
  a.k.a. engineering.
• Methane Bubbles (a.k.a. scientifically combusting
  flatulence SAFELY)
• The point being some gases (i.e. propane,
  octane) are combustible, and are used as fuels.
• Mythbusters
• The point being some gases have medicinal
  purposes.

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Do water and gasoline mix?

• Heres one place where gases behave differently
  than liquids!
• When gasoline (an oil) is mixed in water, theyre
  said to be imiscible in one another (they form
  layers and dont really mix).
• When gas vapor and water vapor come into contact,
  they form homogenous mixtures and do not
  separate.
• Gas mixtures in general form homogenous mixtures
  when placed together, regardless of their
  identities.

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Pressure

• Pressure is a force that acts on a given area. P
  F/A
• In real world speak, pressure is the force exerts
  on the walls of its container.
• The Push-up Demo

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Ways of measuring pressure

• When checking tires, you use the tire gauge
  stick.
• When in the lab, you may use something similar to
  a manometer.

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Sample Manometer Problem

• If the Dh of the columns is .142 meters, what is
  the pressure of the gas?

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Units of Pressure to know!
1 atm 760 mmHg 760 Torr 1.01325 105 Pa
101.325 kPa
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Part II Gas Laws and the Ideal Gas Equation

• CHM 102
• Wednesday, June 27th

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Gas Laws

• Used for changing conditions!
• Boyles- relates pressure and volume.
• Charles- relates temperature and volume.
• Combined Gas Law (just as it sounds)
• Avagadros- relates moles to volume.

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Boyles Pressure-Volume

• Boyle showed that P and V are inversely related
  P constant (1/V)
• So as volume goes up, pressure goes down, and the
  opposite holds true.
• Try replacing P with y and V with X, and you
  get y1/x. What does this look like?

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• Using Boyles Law

• In practice, youll be using
  P1V1 P2V2
• Lets say weve got gas A at 1 atm and 1L, and we
  expand the volume of the container to 4L, holding
  temperature constant throughout. What happens to
  the pressure of the gas?
• ANSWER (1atm)(1L) (x atm)(4L)
• Result ¼ atm. The pressure went down from 1
  atm to ¼ atm.

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Charles Temperature-Volume

• Charles showed that T and V are directly related
  V constant (T) or V kT
• So as volume goes up, temp goes up, and the
  opposite holds true.
• Try replacing V with y and T with x, and you
  get ykx. What does this look like?

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• Using Charles Law

• In practice, youll be using
  V1/T1 V2/T2 Lets say weve got gas A at
  2 L and 150 K, and we raise the temperature of
  the gas to 300 K, holding pressure constant
  throughout. What happens to the volume of the
  gas?
• ANSWER (2 L)/(150 K) (x L)(300 K)
• Result 1 L. The volume went down from 2 L to
  1 L.

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Combined gas Law

• You can combine Charles and Boyles into the
  combined gas law
• (P1V1)/T1 (P2V2)/T2
• This is still used for changing condition
  problems, and works the same way as the previous
  laws!

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• Using the Combined Gas Law

• In practice, youll be using
  (P1V1/T1) (P2V2/T2) Lets say weve got gas A
  at 2 L and 150 K, and we raise the temperature of
  the gas to 300 K, holding pressure at 1 atm.
  What happens to the volume of the gas?
• ANS (1atm2 L)/(150 K)(1atmx L)(300 K)
• Result 1 L. The volume went down from 2 L to
  1 L.

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• The Ideal Gas Equation

• The ideal gas equation can predict the behavior
  of an ideal gas based on pressure (P), volume
  (V), temperature (T), moles (n), and R (constant,
  0.0821 Latm/molK)
• PV nRT
• Real gases may vary from ideal behavior, (well
  talk about this later), but for the most part
  gases adhere well to this equation.

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STP!! Remember this!

• Some gas problems may refer to STP. This stands
  for Standard Temperature and Pressure.
• This just provides a set of conditions that is
  universally known to be at 0 oC and 1 atm.
• 1 mol of an ideal gas occupies 22.4 L at STP!
• So how many moles of an ideal gas are present in
  11.2 L at STP?