Honors Chemistry B - Unit 3: Gas Laws

"you have mass so you matter" - steward

welcome back.

let’s play a game of “some, none, or all” (flip me!)

i give you a statement, you tell me if that statement is true for all, some, or no gases

gases are matter

all

gases are flammable

some

gases are visible

some

gases react

some (REMEMBER: noble gases!)

yay you did it! next section

hi

true or false: gases weigh differently depending on their molar mass

true!

how do gases move?

process called diffusion

• gas moves from high to low concentration

• ie: when you burn a candle you can smell it

why do gases move at different speeds?

• the more weight, the slower the gas is

• or vice versa, the less it weighs the speedier it is

what is the law that relates the speed of gases to their molar mass?

graham’s law

what are the four parts of kinetic molecular theory

gases…

1. are made of tiny particles, travelling in straight lines

2. do not occupy volume

3. collisions between molecules are perfectly elastic

4. no attractive or repulsive forces between the particles

temperature

measure of kinetic energy

volume

amount of space an object occupies

what determines volume for gases?

size of container

pressure

force of gas particles hitting the container

if particles are rapidly and frequently hitting the sides of the container, would the pressure be higher or lower?

higher

how does area affect pressure?

higher area → lower pressure

lower area → higher pressure

magic.

what is STP?

Standard Temperature & Pressure

• pressure → 1 atm

• temperature → 273 K

now we get into the actual gas laws :D

yay

Dalton’s Law, what’s the tea?

Dalton’s Law - Partial Pressure

• the total pressure of a gas mixture = the sum of the different gas components

• not dependent on the weight of the gas, only the amount (it’s why we use moles!)

Example Problem: A mixture of 4.5% H2, 76% O2, and 19.5% N2 has a total pressure of 2.3 atm. What is the partial pressure of each of the gases?

PH2= 0.10 atm; PO2 1.75 atm; PN2= 0.45 atm

Next: Boyle’s Law

Boyle’s Law

• changes pressure and volume

• when moles and temperature are constant, presuure and volume have an inverse relationship

  • when one goes up, other goes down, and vice versa

what kind of container would gas have to be in to undergo Boyle’s Law?

flexible container (like a balloon) because the volume is changing

Example Problem: a gas occupies 1.65L at 1.00 atm what will be the new volume if the pressure becomes 3.00 atm?

0.520L

Charles’ Law

Charles’ Law

• V1/T1=V2/T2

• V and T change, directly related

• n and P are constant

Example Problem: When 10.5 L of gas at 20C is heated, the volume increases to 21 L. What is the new temperature in Celsius? Assume no other changes in the gas.

313 C

Gay-Lussac’s Law

Gay-Lussac’s Law

• P1/T1=P2/T2

• P and T change, directly related

• n and V constant

When a gas has a pressure of 500 mmHg at 25C and is expanded to standard pressure, what happens to the temperature?

The temperature would rise to 452.96 K because the pressure and temperature are directly related

Combined Gas Law

Combined Gas Law

• P1V1/T1 = P2V2/T2

• amount of gas (moles) is the only constant

Ideal Gas Law

PV=nRT

• predicts behavior of gas

• used to find one missing variable when you have the other three

what does the “R” stand for?

“R” → universal gas constant

• 0.0821 (atm x L)/(K x mol)

what is the formula(s) to find molar mass?

M=m/n

• M → Molar Mass

• m → mass

• n → mols

M=dRT/P

how do you find density?

d=m/v