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 = Vibrational (vibrate) Liquids = Rotational (rotate) & Vibrational Gases = Rotational, Vibrational & Translational (move freely from one place to another )

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 elastic 4. There are no attractive or repulsive forces between particles 5. As temperature increases, speed and energy of the particles increases **Large molecules move slowly; Small molecules move quickly

KMT

Properties of Gases 1. Most IDEAL when LOW Pressure and HIGH Temperature Why??? At High T, the gas molecules have a higher average kinetic energy (KEavg) which overcomes the attractive forces. At Low P, the gas molecules are spread further apart and can therefore avoid attractive forces. 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

Properties of Gases Diffusion depends on:  Attractive Forces  ↑ Attractive Forces = ↓ Diffusion  Size of Molecule  ↑ Size = ↓ Diffusion  Speed of Molecule  ↑ Speed = ↑ Diffusion

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.

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

Qualitative Description of Gases 1. Volume vs. Pressure 2. Temperature vs. Volume 3. Temperature vs. Pressure

Qualitative Description of Gases 1. Moles vs. Pressure 2. Moles vs. Volume

Pressure and Temperature Units mmHg torr (1 torr = 1 mmHg) atm (1 atm = 760 mmHg) kPa (1 atm = kPa) Pressure units will be given to Academic Classes only Standard Temperature = 0 o C Standard Pressure = 1 atm

Pressure and Temperature Units K = o C o C = K – Temperature Conversion Equations will be given to Academic Classes only

Pressure and Temperature Units Practice Problems:

Measuring Pressure Barometer=A tube filled with Mercury in a “puddle” of mercury – measures atmospheric pressure

Measuring Pressure Barometer

Measuring Pressure Manometers = Measures pressure of a single gas sample in a container Closed Manometer: Gas Closed End – A vacuum U-Tube with Hg Pgas = Hg Level Difference

Measuring Pressure Open Manometers: Pgas = Patm Pgas = Patm + Hg DiffPgas = Patm – Hg Diff Equal Levels:Higher on Atm Side:Higher on Gas Side: UNITS MUST MATCH!!!!

Summary of Manometers

Manometer Problems Examples

10.3 – Quantitative Description of Gases Gas Laws = Numerical descriptions of gas behaviors 1. Boyle’s Law – Volume and Pressure P 1 V 1 = P 2 V 2 (will be given) Examples:

10.3 – Quantitative Description of Gases 2. Charles’ Law – Temperature and Volume *Temps must be in Kelvin!! (will be given) Examples:

10.3 – Quantitative Description of Gases 3. Gay-Lussac’s Law – Pressure and Temperature *Temps must be in Kelvin!! (will be given) Examples:

10.3 – Quantitative Description of Gases 4. Combined Gas Law – A combination of Boyle’s, Charles’, Gay-Lussac’s *Temps must be in Kelvin!! (will be given) Examples:

Dalton’s Law of Partial Pressures – the total pressure of the gas mixture is equal to the sum of the partial pressures of each individual gas in the mixture P total = P 1 + P 2 + P 3 + … (will be given) Examples: 10.3 – Quantitative Description of Gases

Water Displacement (a form of Dalton’s Law) When a gas is collected by water displacement in the lab, the gas contains not only the experimental gas, it also contains WATER VAPOR from the water evaporating! A calculation using Dalton's Law must be used to determine the pressure of the dry gas (the gas with no water vapor). P total P gas + P H2O = ****P total = P atm {Barometric Pressure!} ****P H2O is given – we look it up in a reference book!

Demos 1. Egg + Flask 2. Balloon + Flask 3. Galileo’s Thermometer 4. Handboiler 5. Drinking Bird 6. Vacuum Pump Tricks 1. Shaving cream 2. Peep 3. Balloon video Balloon video 7. Soda Can Crushing 1. Video Video