Gases. Gases - Concepts to Master What unit of measurement is used for temperature when solving gas law problems? Why? Summarize the Kinetic Molecular.

Gases

Gases - Concepts to Master• What unit of measurement is used for

temperature when solving gas law problems? Why?

• Summarize the Kinetic Molecular Theory.

• What’s the difference between an ideal gas and a real gas?

• Be able to recognize when to use Boyle’s Law and solve problems using the formula.

• Be able to recognize when to use Charles’ Law and solve problems using the formula.

• Be able to recognize when to use Gay-Lussac’s Law and solve problems using the formula.

• Be able to recognize when to use the Combined Gas Law and solve problems using the formula.

• What is the mathematical relationship between pressure and volume?

• What is the mathematical relationship between pressure and temperature?

• Be able to recognize when to use the Ideal Gas Law and solve problems using the formula.

• How does the Kinetic Molecular Theory relate to Boyle’s Law?

• How does the Kinetic Molecular Theory relate to Charles’ Law?

• How does the Kinetic Molecular Theory relate to Avogadro's Law?

• Be able to recognize when to use Avogadro's Law and solve problems using the formula.

• Be able to determine the density of gas based on molar volume.

• Understand Graham’s Law and determine rates of diffusion.

• What is the volume of 1 mole of any gas?

• What is the mathematical relationship between temperature and volume?

• How is Boyle’s law related to breathing?

Vocab• atm• Celsius• Density• Diffusion• Gas constant• Ideal Gas• Kelvin• Kinetic Energy• kPa• mm Hg• Molar volume• Mole• Pressure• Real Gas• STP• Temperature • Volume

Lab• Gas Laws

Properties of Gases

• Often transparent• They can be compressed easily.• They expand to fill their containers.• They take the shape of the container.• Flows easily• Particles have complete freedom of motion

(disordered)• Particles are far apart• They exert pressure on the walls of the

container.• Radon is a radioactive gas that is a problem

in this region.

Kinetic Molecular Theory of Gases1. Gases are composed of a large number of molecules that

behave like hard, spherical objects in a state of constant, random motion.

2. These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space. This is why they can be compressed so easily.

3. There is no force of attraction between gas particles or between the particles and the walls of the container.

4. These particles move in a straight line until they collide with another particle or the walls of the container. These collisions are perfectly elastic. None of the energy of a gas particle is lost when it collides.

5. The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else. 0oC does not correspond with 0 kinetic energy so temperature is measured in Kelvin only.

Boyle’s Law

• Relates Pressure and Volume of a gas

• Temperature MUST be constant to use this law.

• As pressure on the gas increases, the volume decreases.

• FORMULA: P1V1 = P2V2

Breathing and Boyle’s Law

Inhale – Diaphragm LowersVolume increasesPressure decreasesAir rushes in

Exhale – Diaphragm raisesVolume decreasesPressure increasesAir rushes out

Example

Charles’ Law• Relates Temperature and Volume of a gas• Pressure MUST be constant to use this law.• As Temperature of the gas increases, the

volume increases.• FORMULA:

V1 = V2

T1 T2

Charles and Balloons

Pressure is constant (since balloon can stretch).

As air is heated, volume of balloon increases.

As the volume increases, the air inside is less dense thanthe air outside so it rises.

Example

Gay-Lussac’s Law

• Relates Temperature and Pressure of a gas• Volume MUST be constant to use this law.• As Temperature of the gas increases, the

pressure increases. • FORMULA:

P1 = P2

T1 T2

Example

Combined Gas Law

• Relates Temperature, Volume, and Pressure of a gas• Combination of all 3 previous gas laws• Does not require memorization. NONE of the laws do!!!• FORMULA:

P1V1 = P2V2

T1 T2

Example

Graham’s Law• Gases expand to occupy the volume that is available to it.• This is Diffusion – movement from high concentration to

lesser concentration.• Diffusion occurs a different rates depending on the density

of the gas.– T and P are constant– A denser (“heavier”) gas diffuses more slowly.– A less dense (“lighter”) gas diffuses faster.

Hydrogen because it is the lightest with an formula mass of 1g/mol

Water because it is the heaviest with an formula mass of 18g/mol

How the Kinetic Molecular Theory

Explains Boyle’s Law

• Gases can be compressed because most of the volume of a gas is empty space.

• Decreasing volume compresses the gas into a smaller space, but temperature and the number of particles remains constant

• This means that the particles will hit the walls more often. Any increase in the frequency of collisions with the walls of the container must lead to an increase in the pressure of the gas.

How the Kinetic Molecular Theory

Explains Charles Law

• Gas particles move faster as the they become warmer. So they will exert a greater force on the walls of the container each time they hit. This leads to an increase in pressure.

• Since pressure must remain constant, the walls of the container must be flexible.

• The volume of the gas becomes larger as the temperature of the gas increases.

How the Kinetic Molecular Theory

Explains Gay-Lussac’s Law

• If volume is held constant and temperature increases, each particle has a greater speed.

• This increase in speed means that each particle will hit the walls of the container with a greater force.

• This increase in force leads to an increase in the pressure of the gas.

How the Kinetic Molecular Theory Explains Graham’s Law

• If temperature and pressure are held constant, each particle will diffuse based on its density only.

• The more dense gas will diffuse more slowly expands to fill the container.

• The less dense gas will diffuse more quickly as it expands to fill the container.

Avogadro's Law• Relates # of particles in gas sample (n) to

Volume of the sample• T and P are constant• Equal volumes of gases contain equal # of

particles (n).• 1 mole of ANY gas contains 6.02 x 1023

particles.• This corresponds with 22.4 L at STP only!• So 1 mole of ANY gas equals 22.4 L.

V1 = V2

n1 n2

• The volume of the gas is proportional to the number of gas particles.

Avagadro’s Law

Example

Determining Density of a Gas

• D = m/V

• For 1 mole of a substance– D = formula mass/ molar volume– Molar volume = 22.4 L

Example

Ideal Gases vs Real Gases• Ideal Gases behave exactly as predicted by the

Kinetic Molecular Theory.

• Real gases do NOT behave exactly as the theory predicts because:– Gases DO have Volume.– Gases DO attract and/or repel one another.

• Real gases behave MOST LIKE Ideal gases when:– High Temp– Low Pressure– Gas itself is lighter

Real Gas Law

[P+an2] (V-nb) = nRTV2

Correction Factors:

b = measured volum

a = attractive / repulsive forces between the molecules