GASESGASES

Importance of GasesImportance of Gases

• Airbags fill with NAirbags fill with N22 gas in an gas in an accident. accident.

• Gas is generated by the Gas is generated by the decomposition of sodium decomposition of sodium azide, NaNazide, NaN33..

• 2 NaN2 NaN33 ---> 2 Na + 3 N ---> 2 Na + 3 N22

THREE STATES OF MATTERTHREE STATES OF MATTERTHREE STATES OF MATTERTHREE STATES OF MATTER

General Properties of GasesGeneral Properties of Gases

• There is a lot of “free” space There is a lot of “free” space in a gas.in a gas.

• Gases can be expanded Gases can be expanded infinitely.infinitely.

• Gases fill containers uniformly Gases fill containers uniformly and completely.and completely.

• Gases diffuse and mix rapidly.Gases diffuse and mix rapidly.

Properties of GasesProperties of GasesGas properties can be modeled using Gas properties can be modeled using

math. Model depends on—math. Model depends on—• V = volume of the gas (L)V = volume of the gas (L)• T = temperature (K)T = temperature (K)– ALL temperatures MUST be in ALL temperatures MUST be in

Kelvin!!! No Exceptions!Kelvin!!! No Exceptions!– K = C + 273K = C + 273

• n = amount (moles)n = amount (moles)• P = pressureP = pressure

(atmospheres) (atmospheres)

Boyle’s LawBoyle’s LawP P αα 1/V 1/VThis means Pressure and This means Pressure and

Volume are INVERSELY Volume are INVERSELY PROPORTIONALPROPORTIONAL

(mass and Temp are (mass and Temp are constant)constant)

PP11VV11 = P = P22 V V22

As P goes up , V goes As P goes up , V goes down.down.

As P goes down, V goes upAs P goes down, V goes up

Robert Boyle Robert Boyle (1627-1691). (1627-1691). Son of Earl of Son of Earl of Cork, Ireland.Cork, Ireland.

Boyle’s LawBoyle’s LawBoyle’s LawBoyle’s Law

A bicycle pump is a A bicycle pump is a good example of good example of Boyle’s law. Boyle’s law.

As the volume of the As the volume of the air trapped in the air trapped in the pump is reduced, pump is reduced, its pressure goes its pressure goes up, and air is up, and air is forced into the forced into the tire.tire.

Charles’s Charles’s LawLaw

If n and P are constant, If n and P are constant, then V then V αα T T

V and T are directly V and T are directly proportional.proportional.

VV11 V V22

==

TT11 T T22

• If temperature goes If temperature goes

up, the volume goes up, the volume goes up!up!

Jacques Charles (1746-Jacques Charles (1746-1823). Isolated boron 1823). Isolated boron and studied gases. and studied gases. Balloonist.Balloonist.

Charles’s original balloonCharles’s original balloon

Modern long-distance balloonModern long-distance balloon

Gay-Lussac’s LawGay-Lussac’s LawIf n and V are constant, If n and V are constant,

then P then P αα T TP and T are directly P and T are directly

proportional.proportional.PP11 P P22

==

TT11 T T22

• If temperature goes If temperature goes

up, the pressure goes up, the pressure goes up!up!

Joseph Louis Gay-Joseph Louis Gay-Lussac (1778-1850) He Lussac (1778-1850) He was a ballonist.was a ballonist.

Combined Gas Law

• The good news is that you don’t have to remember all three gas laws! Since they are all related to each other, we can combine them into a single equation. BE SURE YOU KNOW THIS EQUATION!

P1 V1 P2 V2

= T1 T2

Combined Gas Law

If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law!

P1 V1

T1

P2 V2

T2

Boyle’s Law

Charles’ Law

Gay-Lussac’s Law

=