Gas Laws

Gas Laws

The fundamental laws of gases or volumetric laws are the following: gas laws chemistry

  • Avogadro’s Law: gas laws chemistry
    • Avogadro discovers in 1811 that at constant pressure and temperature, the same amount of gas has the same volume regardless of the chemical element that forms it.
    • The volume ( V ) is directly proportional to the amount of gas particles ( n ) independent of the chemical element that forms the gas
    • Therefore: 1 / 1 = 2 / 2
    • Which has the consequence that:
      • If you increase the amount of gas, you increase the volume
      • If the amount of gas decreases, the volume decreases
  • Boyle’s Law:
    • Boyle discovered in 1662 l to pressure exerted by a gas is inversely proportional to its volume at constant temperature and gas amount: P = k / V → P · V = k (k is a constant). gas laws chemistry
    • Therefore: 1 · 1 = 2 · 2
    • Which has the consequence that: gas laws chemistry
      • If the pressure increases the volume decreases 
      • If the pressure decreases the volume increases
    • Note : It is also called the Boyle-Mariotte Law as he discovered it independently in 1676 .
  • Charles Law: gas laws chemistry
    • Charles discovered in 1787 and l volume of gas is directly proportional to the temperature at constant pressure: V = k · T (k is a constant).
    • Therefore: 1 / 1 = 2 / 2
    • Which has the consequence that:
      • If the temperature increases the volume increases
      • If the temperature decreases the volume decreases
    • Note : Also called Charles and Gay-Lussac’s Law.
  • Gay Law – Lussac:
    • Gay-Lussac discovers in 1802 that the pressure of the gas is directly proportional to its temperature at constant volume: P = k · T (k is a constant).
    • Therefore: 1 / 1 = 2 / 2
    • Which has the consequence that: gas laws chemistry
      • If the temperature increases the pressure increases
      • If the temperature decreases the pressure decreases
  • Ideal Gas Law: gas laws chemistry
  • Ideal gases have the following properties:
    • Gas molecules move at high speeds in a linear but disorderly manner
    • The speed of the gas molecules is proportional to their absolute temperature
    • The gas molecules exert sustained pressure on the walls of the container that contains it.
    • The collisions between the gas molecules are elastic so they do not lose kinetic energy
    • The attraction / repulsion between gas molecules is negligible gas laws chemistry
    • For these ideal gases the following law is fulfilled:

P · V = n · R · T

    • Where n are the moles of the gas and R the universal constant of the ideal gases. gas laws chemistry
  • General Gas Law: gas laws chemistry
    • The General Gas Law consists of the union of the following laws:
      • Boyle ‘s law: 1 · 1 2 · 2
      • Gay-Lussac’s Law: 1 / 1 2 / 2
      • Charles Law: 1 / 1 2 / 2
    • All of them are condensed into the following formula:

1 · 1 1 2 · 2 2

  • Graham’s Law: 
    • Formulated by Graham discovered in 1829:
    • The rates of effusion (exit through pores) and diffusion (expansion until occupying the volume of the container) of gases are inversely proportional to the square root of their molar masses: gas laws chemistry

1 2 = ( 2 1 ) -1/2

    • where: 1 , 2 are the diffusion / effusion masses of the gas and 2, M 1 are the molar masses
  • Dalton’s Law:
    • Formulated by Dalton in 1801.
    • The total pressure of a gas mixture is equal to the sum of the pressures exerted by each of the gases that compose it.
    • The pressure exerted by each gas in the mixture is called Partial Pressure. Therefore this law can be expressed as:

Total 1 + 2 + … + n

    • Where 1 , 2 , …, n are the partial pressures of each of the gases in the mixture. gas laws chemistry
  • Henry’s Law: 
    • Made by Henry in 1803.
    • The amount of gas dissolved in a liquid at constant temperature is proportional to the partial pressure of the gas above the liquid.
    • This law is summarized in the following equation:

p H · c

    • Where: p : partial pressure of the gas, c : concentration of the gas and H : Henry’s constant. gas laws chemistry

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