The Gas Laws. Boyle’s Law Charles’ Law Gay-Lussac’s Law Avogadro’s Law. Boyle’s Law. Boyle’s Law – at constant temperature , the volume of the gas increases as the pressure decreases. The volume of the gas decreases and the pressure increases. V ↑ P↓. Volume L. P 1 V 1 = P 2 V 2.
Boyle’s Law – at constant temperature, the volume of the gas increases as the pressure decreases. The volume of the gas decreases and the pressure increases.
P1V1 = P2V2
If you squeeze a gas sample, you make its volume smaller.
Volume is 100 mL at 25°C
Volume is 50 mL at 25°C
In which system is the pressure higher? (Which has the greater number of collisions with the walls and each other?)
Charles’ Law – at a constant pressure, the volume of a gas increases as the temperature of the gas increases and the volume decreases when the temperature decreases.
Steel cylinder (2L)
contains 500 molecules of O2 at 400 K
Steel cylinder (2L) contains 500 molecules of O2 at 800 K
Gay-Lussac’s Law – the pressure of a gas is directly proportional to its absolute temperature at a constant volume.
P T V
Think “Public Tele Vision”
Boyle’s Law – Temperature is constant
Charles’ Law – Pressure is constant
Gay-Lussac’s Law – Volume is constant
The equation is found on Table T. Note that all temperatures must be in Kelvin!
1000 mL = 1L
1 atm = 101.3 kPa
1 atm = 760 mm Hg
1 atm = 760 torr
Avogadro’s Law – equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
1 mole of ANY gas takes up a volume of 22.4 L at STP.
Entropy is the randomness of particles.
Effusion – the passage of gas under pressure through a small opening. (Gases effuse through a hole in your tire!)
Graham’s Law – Particles of low molar mass travel faster than heavier particles.
Hydrogen effuses 4 times faster than oxygen.
Dalton’s Law of Partial Pressure -
In a mixture of gases, each gas exerts a certain pressure as if it were alone. The pressure of each one of these gases is called the partial pressure. The total pressure of a mixture of gases is the sum of all of the partial pressures.
Ptotal = PA + PB + PC
A closed cylinder contains 3L of He, 1L of H2 and the total pressure in the system is 800 torr. What is the partial pressure of the He?
Ptotal = PA + PB + PC
3L + 1L = 4L AND 4L = 800 torr
4L = 800 torr
4 4 → 1L = 200 torr
1L H2 200 torr
3L He 600 torr
4L gas 800 torr