Chapter 10 – Gas Laws. Kinetic Molecular Theory (KMT) Particles of matter are always in motion. The KMT describes any property based on the particle motion.

Chapter 10 – Gas Laws

Kinetic Molecular Theory (KMT)

Particles of matter are always in motion.

The KMT describes any property based on the particle motion

Review: Solids = Rotational

Liquids = Rotational & Vibrational

Gases = Rotational, Vibrational & Translational

KMT

Ideal Gas = A gas that acts “perfectly” as expected. Does not really exist, but it is possible to be close to it.

KMT - Assumptions

1. Gases are made of large numbers of tiny particles

2. Particles of a gas are in random, constant straight line motion

3. Collisions of particles are elastic4. There are no attractive or repulsive

forces between particles5. As temperature increases, speed and

energy of the particles increases

http://mc2.cchem.berkeley.edu/Java/molecules/

KMT

KMT

KE = ½ mv2

**Large molecules move slowly; Small molecules move quickly

Properties of Gases

1. Most IDEAL when LOW Pressure and HIGH Temperature

Why???

2. Expansion – Fill entire container

3. Fluidity – Flow due to minimal external bonds

4. Low Density – d = m/v

Properties of Gases

5. Compressibility – Can push particles together to make smaller total volume

6. Diffusion – Mix / Spread out without stirring

Rate1/Rate2 = √Molar Mass2/√M Mass1

Example: How much faster is Hydrogen compared to Oxygen Gas?

Real vs. Ideal Gases

Real Gas = Gas that disobeys an assumption of the KMT of Gases

1. The particles of a real gas have volume themselves. This is ignored by the KMT.

2. Particles of a real gas have attractive and repulsive forces. These are ignored by the KMT.

Qualitative Description of Gases

• Volume of the gas sample

• Pressure – Caused by gas particles hitting the sides of the container

• Temperature of the gas sample

• Number of moles (particles) of the gas


1. Volume vs. Pressure

2. Temperature vs. Volume

3. Temperature vs. Pressure


4. Moles vs. Pressure

5. Moles vs. Volume

Pressure and Temperature Units

mmHg

torr (1 torr = 1 mmHg)

atm (1 atm = 760 mmHg)

kPa (1 atm = 101.325 kPa)

Pressure conversion chart will be given to Academic Classes only

Standard Temperature = 0oCStandard Pressure = 1 atm

STP =


Temperature Conversion Equations will be given to Academic Classes only

K = oC + 273.15

oC = K – 273.15


Practice Problems:

Measuring Pressure

Barometer=A tube filled with Mercury in a “puddle” of mercury.

Measuring Pressure

Barometer

Measuring Pressure

Manometers = Measures Pressure of a Gas Sample

Closed Manometer:

Gas

Closed End – A vacuum

U-Tube with Hg

Pgas = Hg Level Difference

Measuring PressureOpen Manometers:

Pgas = Patm Pgas = Patm + Hg Diff Pgas = Patm – Hg Diff

Equal Levels: Higher on Atm Side: Higher on Gas Side:

Skip P=F/A

10.3 – Quantitative Description of Gases

Gas Laws = Numerical descriptions of gas behaviors

1. Boyle’s Law – Volume and PressureP1V1 = P2V2 (will be given to Academic)Examples:


2. Charles’ Law – Temperature and Volume*Temps must be in Kelvin!!

(will be given to Academic)

Examples:

1 2

1 2

V V

T T


3. Gay-Lussac’s Law – Pressure and Temperature

*Temps must be in Kelvin!!


Examples:

1 2

1 2

P P

T T


1 1 2 2

1 2

P V P V

T T

1 1 2 2

1 2

P V P V

T T

4. Combined Gas Law – A combination of Boyle’s, Charles’, Gay-Lussac’s


This is really the only one you need to know!


If Temperature is CONSTANT = = P1V1 = P2V2

If Pressure is CONSTANT = =

1 2

1 2

V V

T T

1 1 2 2

1 2

P V P V

T T


4. Combined Gas Law – A combination of Boyle’s, Charles’, Gay-Lussac’s


(will be given to Academic)1 1 2 2

1 2

P V P V

T T

Examples:

More Practice:


Dalton’s Law of Partial Pressures

Ptotal = P1 + P2 + P3 + …


Examples:

Water Displacement (a form of Dalton’s Law)Collecting Gas THROUGH Water

The gas collected contains not only the experimental gas, it also contains WATER VAPOR from the water evaporating!

The container is moved either up or down to make the gas levels EQUAL. This makes the PRESSURE INSIDE = PRESSURE OUTSIDE!

Ptotal = Patm Pgas + PH2O =

Demos

1. Balloon + Flask

2. Galileo’s Thermometer

3. Handboiler

4. Drinking Bird

5. Vacuum Pump Tricks

6. Egg + Flask

7. Soda Can Crushing

Chapter 10 – Gas Laws. Kinetic Molecular Theory (KMT) Particles of matter are always in motion. The KMT describes any property based on the particle motion.

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