CatalystReview your Mock AP exam score and complete

the reflection sheetTurn into bin when completed.

Overall Score Distribution

Period 5

Period 2

Where We Are At

We have made huge gains, but we have more

work to do!

Score Distribution

Heel Spurs

How Painful Are Those Shoes?

Lecture 4.1 – Pressure and Gas Laws

Today’s Learning TargetsLT 4.1 – I describe what the pressure of a gas

indicates and I can calculate the pressure of a given substance.

LT 4.2 – I can discuss the four gas laws (Gay – Lussac, Charles, Boyle, and Avogadro) and solve complex equations that integrate one or more of these using calculations.

LT 4.3 – Using the four gas laws, I can derive the Ideal Gas Law. Additionally, I can solve and apply this equation to a wide variety of situations (density, molar mass, etc.)

GasesRecall, gases are moving in constant random

motionThey fill the entire container that they are

contained in.

PressurePressure is the force

exerted over a given areaForce is measured in

Newtons ( ).Area is measured in m2

Pressure is measured in Pascals (Pa)Other units of pressure

include atmospheres, mm Hg, torr, and bar

€

P =F

A

€

kg⋅ms2

Atmospheric PressureThe atmosphere exerts a

pressure on all objectsGas molecules are constantly

colliding with our bodies, create the observed pressure.

Less gas molecules the higher you go up in the atmosphere, therefore atmospheric pressure drops

At sea level atmospheric pressure is:100 kPa1 atm1 barr760 mm Hg

Converting Between Pressure Units

1 atm = 1.01325 bar 1 atm = 760 mm Hg 1 atm = 760 torr 1 atm = 100 kPa

Measuring PressurePressure is measured using a barometerAt atmospheric pressure, a tube without any

gas, open at one end and immersed in mercury will have the mercury rise 760 mm.

MonometersThe sample gas is

placed at one end of the tube filled with mercury.

The height is added to the initial mercury reading to get the pressure of the gas of interest.

Class ExampleAn open end manometer

with atmospheric pressure at 760. mmHg, and the mercury level was 120. mm higher on the right side than the left. What was the gas pressure in atm?

Table TalkOpen end manometer,

atmospheric pressure 755 mmHg, Hg level 75 mm higher on the right. What was the gas pressure in torr?

Standard Temperature and Pressure (STP)Many problems are run

at standard temperature and pressure.

Standard Temperature = 273.15 K or 0 oC

Standard Pressure = 1 atm

Around the WorldAround the room, there are 8 questions.Answer all 8 questions and check your answers

on the back side of the sheet.

Boyle’s LawIf we keep temperature constant, then

volume and pressure are inversely related. As one goes up the other goes down

Therefore, we can describe this relationship as:

€

V α 1

P

Boyle’s Law

Graph of Boyle’s Law

This is an inverse relationship! As one goes up the other

goes down!

Charles LawAs you heat up gas molecules they move

quicker and this causes them to hit the sides of the container with greater frequency.

If the container is capable of expanding,, then the volume will increase as the temperature increases.

Therefore, we can describe this relationship as:

€

V α T

Charles Law Graph

This is a direct relationship!

Gay – Lussac’s LawGas molecules move quicker the more we

heat them up and increase the temperature.This means that they will be hitting the sides

of the container more often and the pressure will also increase as the temperature increases.

We describe this by:

€

P α T

Gay-Lussac’s Law

Gay-Lussac’s Law

Absolute Zero

This is an direct relationship! As one goes up the other goes up!

Avogadro’s LawRecall that if you have 1 mole of any gas, then

it occupies 22.4 LThis means that

€

V α n

Ideal GasAn ideal gas is a theoretical gas that is made of

randomly moving particles that do not interactMost real gases behave like ideal gases at

atmospheric pressure and 0 oC.

Deriving the Ideal Gas LawWe know:

€

V α 1

PV α T

V α n

The Ideal Gas Law

P = PressureV = Volumen = MolesT = TemperatureR = Gas Constant = 0.08206

€

PV = nRT

€

L⋅ atmmol⋅K

Class ExampleCalcium carbonate decomposes upon heating

to CaO and CO2. A sample of CaCO3 is decomposed, and the carbon dioxide is collected in a 250 mL flask. After decomposition is complete, the gas has a pressure of 1.3 atm at a temperature of 31 oC. How many moles of CO2 gas were generated?

Table TalkTennis balls are usually filled with either air or

N2 gas to have a pressure above atmospheric pressure to increase their bounce. If a tennis ball has a volume of 144 cm3 and it contains 0.33 g of N2 gas, what is the pressure inside the ball at 24 oC? HINT – 1 mL = 1 cm3.

Ideal Gas Law and DensityDensity is calculated by:

We also know that if we have moles and want grams, then we use the molar mass to convert:

Therefore, we can calculate the density of our gas by:€

d =m

V

€

n =m

MW

€

Density =n⋅Molar Mass

V=P⋅Molar Mass

RT

Class ExampleWhat is the density of carbon tetrachloride

vapor at 714 torr and 125 oC

Table TalkThe mean molar mass of the atmosphere at

the surface of Titan, Saturn’s largest moon, is 28.6 g/mol. The surface temperature is 95 K, and the pressure is 1.6 atm. Assuming ideal behavior, calculate the density of Titan’s atmosphere.

Molar Mass and Ideal Gas LawWe can rearrange our density equation to

calculate the molar mass of a gas:

€

Molar Mass =dRT

P

Class ExampleCalculate the molar mass of a gas if 2.50 g

occupies 0.875 L at 685 torr at 25 oC

Table TalkCalculate the molar mass of a vapor that has a

density of 7.135 g/L at 12 oC and 743 torr

White Board Races

Question 1At what temperature does 16.3 g of nitrogen

gas have a pressure of 1.25 atm in a 25.0 L tank?

Question 2What mass of CO2 is needed to fill an 80.0 L

tank to a pressure of 150.0 atm at 27.0°C?

Question 3Calculate the density of HCl at STP

Question 410 L of an unknown gas has a mass of 10.8

grams at a temperature of 310 K and 1.2 atm. What is the molar mass of this mass? What is the identity of the gas?

Question 5A gas mixture of helium and argon has a

density of 0.704 g/L. What is the percent composition of the mixture by mass.

Closing TimeClosing TimeRead 10.1 – 10.5 and answer essential

questions on reading guideComplete book questions: 10.2, 10.4, 10.5,

10.13, 10.21 (skip e), 10.25, 10.33, 10.36, 10.38, 10.39, 10.53, and 10.54