Gases…..

Have neither shape nor volume

Are highly compressible

Diffuse (move spontaneously throughout any

available space until equally distributed)

Temperature affects either the volume or pressure of a gas or both

Pressure

is defined as a force per unit areaSince force can be measured in NewtonsAnd area can be measured in m2

Then N/m2 is the unit which is the SI definition of a pascal

we measure pressure in kilopascal (kPa)

Pressure

Atmospheric pressure is the force per unit area exerted by air on ALL objects

Standard conditions

STP

0 oC101.325 kPa

SATP – more convenient25 0C100kPa

Other pressure units!!

Manometer

Effusion

Boyle’s Law

As pressure on a gas increases, the volume of the gas decreases proportionally, provided that that temperature and the chemical amount(moles) of gas remains constant

So

PV

1

Boyle’s Law

2211

2211

:

:

:

PVPV

Summarized

PVkPVthen

kPVSince

Boyles Law

Volume

Pre

ssu

re

Temperature

is defined as the average kinetic energy of particles

We usually measure it in oC but for gases we will use the absolute or

Kelvin temperature scaleTo convert from celsius simply add 273

Charles’ Law

As temperature of a gas increases, the volume of the gas increases proportionally, provided that that pressure and the chemical amount(moles) of gas remain constant TV

TV

Charles’ Law

2

2

1

1

2

2

1

1

:T

V

T

VCombined

T

Vk

T

Vthen

kT

VSince

Charle's Law

Temperature

Vo

lum

e

14

Combined Gas Law

2

2 2

1

1 1

T

Vx P

T

Vx P

• Combination of Boyles and Charles’ Law and (Gay Lussac)

• Unchanging conditions drop out of the equation• Remember temp MUST be in Kelvin

Molar Volume

Molar volume is the volume that one mole of a gas occupies at a specified temperature and pressure…..At STP 22.4 litres in one mole of a gasAt SATP 24.8 litres in one mole of a gas

How do you convert between moles and volume??

How do you convert between mass and volume….one extra step!

Example problem 1

What is the volume of 0.24moles of CO2 (g) at STP??

Example Problem 2

What is the volume of 6.8g of Hydrogen gas at SATP??

Perform the following conversions (all at SATP).

1. 4.00 mol CH4(g) to L

2. 2.25 mol NO(g) to L

3. 4.275 g CO2(g) to L

4. 1.27 g H2(g) to L

5. 5.00 L O2(g) to mol O2(g)

6. 3.50 L H2(g) to mol H2(g)

7. 4.35 L CH4(g) to g CH4(g)

8. 5.45 L N2(g) to g N2(g)

Practice

Section questions #5-10 p. 171

How can you get an egg in and out of a flask?????

Ideal Gas Law

What makes an “ideal gas” hypothetically???

They obey ALL gas laws perfectly under ALL conditions

SO….they do not condense

….graphs of v/T and p/T are straight lines

….particle size is negligible with NO intermolecular attractions between them

REAL gases are most ideal when

Pressure is ? LOW Because…..at high pressure molecules are forced

together and their size becomes significant relative to the empty space in container

Temperature is ? HIGH Because…..at low temperature molecules are

closer together, moving slower and thus experience intermolecular attraction (they condense)

Simulation for Gas Laws

TV

PV

1

nV

pTnV

1

Therefore

24

Ideal Gas Law

PV = nRT

R is called the gas constant (combined gas law constants)

R = 8.314 kPa.L mol.K

Pressure MUST be in kPa and Volume in L and temp in Kelvin

25

So many gas laws eh?

26

Sample problem 4.4Predict the volume of 0.78g of Hydrogen gas at 22°C and 125kPa

Practice #3-5 p.175 and SQ #8,9,11, p. 176

Explaining Gas Properties

What is kinetic molecular theory??

Kinetic molecular theory

solid(vibrational

)

liquid(vibrational, rotational,

and translational)

gas(translational)

29

Kinetic Molecular Theory

30

Gas PressurePressure = total force applied to a certain area larger force = larger

pressuresmaller area = larger

pressure

• Gas pressure is caused by gas molecules colliding with the container or surface

• More forceful collisions or more frequent collisions mean higher gas pressure

31

Compressing a gas!

Law of combining volumes

1809….Joseph Gay-Lussac

Law of combining volumes

1811…Amedeo Avogadro

e.g.

http://science.nelson.com/ABchem20-30/teacher/protect/audio/unit2ch4.html#4.2

Practice Questions #4-7, p.166 and p168 #1-5