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: V ₁ / n ₁ = V ₂ / n 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: P ₁ · V ₁ = P ₂ · V 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: V ₁ / T ₁ = V ₂ / T 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: P ₁ / T ₁ = P ₂ / T 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: P ₁ · V ₁ = P ₂ · V ₂
    • Gay-Lussac’s Law: P ₁ / T ₁ = P ₂ / T ₂
    • Charles Law: V ₁ / T ₁ = V ₂ / T ₂

• • All of them are condensed into the following formula:

P ₁ · V ₁ / T ₁ = P ₂ · V ₂ / T 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

v ₁ / v ₂ = ( M ₂ / M ₁ ) ^-1/2

• • where: v ₁ , v ₂ are the diffusion / effusion masses of the gas and M _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:

P _Total = p ₁ + p ₂ + … + p _n

• • Where p ₁ , p ₂ , …, p _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 = k _H · c

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