The Gas Laws

1.Boyle’s Law 2.Charles’ Law 3.Gay-Lussac’s Law 4.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↓

V 1 1 2 2 o P V = P V l u If you squeeze a m gas sample, you e make its volume L smaller.

Pressure (kPa) Now . . . a container where the volume can Moveable change (syringe) piston ↕

Same temperature

Volume is 100 mL at Volume is 50 mL at 25°C 25°C

In which system is the pressure higher? (Which has the greater number of collisions with the walls and each other?) Charles’ Law

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. V1 V2 = T1 T2 • increase AKE V • increase the speed of o the particles l • the walls of a flexible u m container expand – e think of hot air balloons! L

Temperature (K) Steel cylinder (2L) Steel cylinder (2L) contains 500 contains 500 molecules of O2 at molecules of O2 at 400 K 800 K

1. In which system do the O2 molecules have the highest average kinetic energy? B 2. In which system will the particles collide with the container walls with the greatest force? B 3. In which system is the pressure higher? B Gay-Lussac’s Law Gay-Lussac’s Law – the pressure of a gas is directly proportional to its absolute temperature at a constant volume.

P1 P2 Pressure = (atm) T1 T2

Temperature (K) To remember how these work. . .

P T V

Think “Public Tele Vision” To remember which constants go with which law . . .

Boyle’s Law – Temperature is constant BLT

Charles’ Law – Pressure is constant Cheese Pizza

Gay-Lussac’s Law – Volume is constant Green Veggies Combined Gas Law

P1V1 = P2V2 T1 T2

The equation is found on Table T. Note that all temperatures must be in Kelvin! Units used to describe gas samples:

Volume Temperature Pressure Liter (L) Kelvin ONLY Atmosphere (atm) Milliliter (mL) Kilopascale (kPa) 1000 mL = 1L 1 atm = 101.3 kPa 1 atm = 760 mm Hg 1 atm = 760 torr Avogadro’s Law Avogadro’s Law – equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

2 H O2 CO2

1 mole of ANY gas takes up a volume of 22.4 L at STP.  YouTube - Chemistry Music Video 7: Rock Me Avogadro

Kinetic Molecular Theory - continued  Gas temperature is proportional to average kinetic energy.

 Heat increases the energy of random motion of a gas. Not all molecules are traveling at the same speed. As a result of multiple collisions, the molecules have a range of speed. Ideal Gases • Gases whose behavior can be predicted by the kinetic molecular theory are called ideal, or perfect, gases. No gases are truly ideal because no gas totally obeys all of the gas laws.

• An ideal gas is an imaginary gas that is perfect and does follow everything perfectly. Ideal Gases, continued

 An ideal gas does not condense to a liquid at low temperatures  An ideal gas does not have forces of attraction or repulsion between particles  An ideal gas is composed of particles that have no volume. Real Gas Vs. Ideal Gas

 A real gas is most like an ideal gas when the real gas is at a low pressure and a high temperature.  The gases that act most like ideal gases are the small mass ones – hydrogen and helium. Diffusion

• movement of particles from areas of high concentrations to areas of low concentration. •Gases diffuse and mix with other gases very rapidly due to their rapid motion. (Think ammonia, tuna or skunk smell.) •It eventually reaches equilibrium and the mixture is homogeneous.

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!) Two More Laws!!

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 Example:

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

 YouTube - MythBusters - Fun With Gas