Gay-Lussac’s Gay-Lussac’s LawLaw

Pressure vsPressure vs TemperatureTemperature

Gay-Lussac (1778-1850)Gay-Lussac (1778-1850)•balloonistballoonist

•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 function atmosphere as function of altitudeof altitude

Gay-LussacGay-Lussacexamined relationship between P & T at examined relationship between P & T at constant V and # molesconstant 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 between pressure results from collisions between gas molecules & walls of containergas molecules & walls of container– so, if T , expect P so, if T , expect P

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

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

Gay-Lussac’s LawGay-Lussac’s Law

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

P/T = kP/T = k

Gay-Lussac’s Law: Gay-Lussac’s Law: mathematicallymathematically

PP11 = = PP22

TT11 T T22

OR OR

PP11TT22 = T = T11PP22

Gay-Lussac’s Law:Gay-Lussac’s Law: verbally verbally

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-Lussac’s Law:Gay-Lussac’s Law: graph graph

(K)

what kind of relationship is this? direct

graph: straight line with y-intercept of zero

P vs T of a gas