Molar Volume

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Molar Volume
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Molar Volume

• There is a way to relate the volume of a gas to
  the amount of gas in moles.
• The volume of a gas is related to both its
  temperature and its pressure
• This must be considered to understand the
  relationship between volume and moles

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Temperature and Pressure

• Both affect the volume of gases
• Example-Balloon in freezer
• If temperature decreases, volume of gas decreases
• Example-Diver in deep ocean
• If pressure is increased, volume of gas is
  decreased

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Standard temp and press

• Standard conditions
• -The average pressure of the atmosphere at sea
  level is taken as standard pressure which is
  101.3kPa
• -The freezing point of water is defined as
  standard temperature, which is 0C or 273K
• Together these conditions are known as standard
  temperature and pressure or STP

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Avogadros Hypothesis

• Used the findings of Guy-Lussac and Dalton
• Avogadro said equal volumes of all ideal gases
  at the same temp. and press. contain the same
  number of molecules
• Mathematically
• naV or nkV or n1/V1n2/V2
• Based on the law, one mole of gas occupies the
  same volume as one mole of another gas at the
  same temp and pressure
• Molar volume of a gas us the space that is
  occupied by one mole of the gas. UnitsL/mol

Where n of moles, Vvolume, and ka constant
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Standard Molar Volume

• The molar volume of a gas at STP is 22.4L/mol
• Can use this number to solve gas problems
  involving moles and volume at STP

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Example

• What is the volume of 3.0mol of nitrous oxide,
  NO2(g), at STP?

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Solution

• We know 1.00mol of gas occupies 22.4L at STP so
  this tells us that n11.0mol and V122.4L
• The question tells us that the n2 is 3.0mol of
  NO2
• All we have to do is use the equation (avogadros
  law)and solve for V2

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Solution

• n1/V1n2/V2
• V2n2V1
• n1
• V2(3.0mol)(22.4L)
• 1.0mol
• V267L

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Example

• Suppose you have 44.8L of methane gas at STP
• a) How many moles are present?
• b) What is the mass of the gas?(g)
• c) How many molecules of gas are present?

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Solution

• Using Avogadros law
• n2n1V2
• V1
• 1.00mol x 44.8L
• 22.4L
• 2.00mol