Topic: Topic: Gay-LussacGay-Lussac’’s Laws LawDo Now: Do Now:

Gay-Lussac (1778-1850)Gay-Lussac (1778-1850)•was a balloonistwas a balloonist

•1802: climbed to 1802: climbed to 23,000 feet 23,000 feet record stood for 50 yearsrecord stood for 50 years

•investigated investigated composition of composition of atmosphere as atmosphere as function of altitudefunction of altitude

Gay-LussacGay-LussacExamined relationship between P & T Examined relationship between P & T at constant V and # molesat constant V and # moles

As T : As T : – gas molecules move faster, collide with gas molecules move faster, collide with

walls more frequently & more energeticallywalls more frequently & more energetically

Pressure results from collisions Pressure results from collisions between gas molecules & walls of between gas molecules & walls of containercontainer– So, if T , expect P So, if T , expect P

Based on the last Based on the last slide, explain in slide, explain in your own words your own words why a balloon why a balloon

expands when the expands when the temperature is temperature is

increaseincrease

Which Which temperature temperature scale has a scale has a direct direct relationship to relationship to molecular molecular velocity?velocity?

KelvinKelvin

Typical data from a Gay-Lussac type experimentTypical data from a Gay-Lussac type experiment What kind of relationship is illustrated in this graph?What kind of relationship is illustrated in this graph?

(K)(K)

Gay-LussacGay-Lussac’’s Laws Law

Relationship between P & T Relationship between P & T at constant volume & # molesat constant volume & # moles

P = kT or P/T = kP = kT or P/T = k

– ItIt’’s direct relationships direct relationship– Straight line with y-intercept of zero Straight line with y-intercept of zero

Gay-LussacGay-Lussac’’s Law: wordss Law: words

pressure exerted by confined gas is pressure exerted by confined gas is directly related to Kelvin temperature at directly related to Kelvin temperature at constant volume & # molesconstant volume & # moles

Gay-LussacGay-Lussac’’s Laws Law

PP11 = = PP22

TT11 T T22

REMEMBER ALL TEMPERATURE MUST BE CONVERTED TO KELVIN

When temperature decreases, the When temperature decreases, the pressure of a gas _____________pressure of a gas _____________

(decreases, increases, stays the (decreases, increases, stays the same)same)

When temperature increases, the When temperature increases, the pressure of a gas ___________pressure of a gas ___________

(decreases, increases, stays the (decreases, increases, stays the same)same)

DecreasesDecreases

IncreasesIncreases