gaseous state

• Gases


  Form of matter that lacks a defined shape or volume
• Gas properties


  • Compressibility - Gases are easy to compress
  • Expandability - expand to completely fill their containers
  • Extremely low density
  • Exert pressure equally in all directions
  • Mix evenly and completely in all proportions
• Number of moles (n)


  One of the key variables that determines the state of a gas
• Temperature (T)


  One of the key variables that determines the state of a gas
• Pressure (P)


  One of the key variables that determines the state of a gas

  
• Volume (V)


  One of the key variables that determines the state of a gas

  
• Pressure


  The force exerted per unit area
• Pascal (Pa)


  SI unit of pressure, equal to 1 N/m^2

  
• Barometer


  Device for measuring atmospheric pressure
• The water column in a barometer would be higher than the mercury column because the density of water is less than the density of mercury

  
• Manometer


  Device for measuring the pressure of a gas or liquid in a vessel

  
• Gases under moderate conditions behave quite simply with respect to T, P, V, and n
• Gases are compressible, i.e. ability to be squeezed when pressure is applied
• Boyle's Law


  The volume of a gas varies inversely with the applied pressure at constant temperature

  
• The volume of a gas is halved when the pressure is doubled, and the volume is reduced to one-third when the pressure is tripled
• Boyle's experiment relating pressure and volume

  1. 1.00-g sample of O2 gas at 0°C placed in container at 0.50 atm, volume is 1.40 L

  2. Pressure doubled to 1.0 atm, volume reduced to 0.70 L

  
• Charles's Law


  The volume of a gas is directly proportional to the absolute temperature at constant pressure

  
• Decrease in temperature results in decrease in volume of a gas
• The temperature -273.15°C is called absolute zero, the temperature at which the volume of a gas is hypothetically zero
• Avogadro's Law


  Equal volumes of any two gases at the same T and P contain the same number of molecules
• Calculating volume change with pressure and temperature change

  Given: Vi = 38.7 mL, Pi = 751 mmHg, Ti = 21°C

  2. Pf = 359 mmHg, Tf = 21°C

  3. Vf = (Pi*Vi)/Pf = 81.0 mL

  
• Standard Temperature and Pressure (STP) is 0°C and 1 atm
• Molar volume at STP

  22.4 L/mol
• Ideal Gas Law


  PV = nRT
• The amount (moles) of gas is proportional to the pressure at constant temperature and volume
• Calculating mass of gas in a cylinder

  Given: V = 50.0 L, P = 17.1 atm, T = 23°C = 296 K

  2. n = PV/RT = 35.20 mol

  3. Mass = n * molar mass of N2

  
• Yellow box


  22.4 L
• To the left of the yellow box

  • A basketball
• Molar gas constant, R

  Constant of proportionality that relates the molar volume of a gas to T/P

  
• Using the Ideal Gas Law

  1. Put varying amounts of a gas into a given container at a given temperature

  2. Show that the amount (moles) of gas is proportional to the pressure at constant temperature and volume

  
• RT/V is constant
• nRT/PV = 1
• Nitrogen, N2


  • 50.0 L cylinder
  • Pressure of 17.1 atm at 23°C
• Calculating the mass of nitrogen in the cylinder

  1. Use the Ideal Gas Law to find the moles

  2. Convert moles to mass using molar mass
• Gas density and molar mass

  • Using the Ideal Gas Law, it is possible to calculate the moles in 1 L at a given temperature and pressure
  • The number of moles can then be converted to grams (per liter)
  • To find molar mass, find the moles of gas, and then find the ratio of mass to moles
• Calculating the density of methane gas, CH4, at 125°C and 3.50 atm

  Use the Ideal Gas Law to find the density

  
• Finding the vapor density of octane

  Use the Ideal Gas Law to calculate the molar mass of octane

  
• The empirical formula of octane is C4H9
• The molecular formula of octane is C8H18
• Stoichiometry and Gas Volumes

  Use the Ideal Gas Law to find moles from a given volume, pressure, and temperature, and vice versa