The Gas Laws

APChemistry

e.g., gasoline vapors

Basics on Gases

composition of the atmosphere: ~78% N2, ~21% O2

properties of gases: expand to fill containercompressibleform homogeneous mixtures

vapors: gases of substances that are normally liquids or solids

-- due to gas particles being…

1)

2)

far apart

in constant, random motion

F Equation for pressure:

AF

P A

N

m2

P N/m2 = Pa

1 atm… = 760 mm Hg= 760 torr= 101.325 kPa= 1.01325 bar

(1 bar = 105 Pa)

At a depth of 350 m (1150 ft), the hull pressure on a submarine

is 3.4 x 106 Pa (36 tons/ft2).

BAROMETER

airpressure

mercury (Hg)

vacuum

mercurybarometer

Close-up of an early mercury barometer,

showing how the mercury column is

supported by atmospheric pressure.

An aneroid barometer containsa small, pressure-sensitive

metal box that has beenevacuated of air. The box is

prevented from collapsing bybeing connected to a spring

that is also attached to the dialon the barometer. When

the air pressure on the wallsof the box changes, the box

“flexes,” which moves thespring and the dial.

OPEN END MANOMETER

CLOSED END MANOMETER

air pressure

Hg heightdifference

sealed end

confinedgas

SMALL + HEIGHT = BIG Pgas = HEIGHT

The Gas LawsBoyle’s law:

Robert Boyle(1627–1691)

PV = constant

(when T is constant)

P

V

V

1/P

Charles’s law:

Jacques Charles(1746–1823)

V/T = constant

(when P is constant)

T

V

**T in K

(0.00 K = –273.15oC)

Gay-Lussac’s law:

Joseph LouisGay-Lussac(1778–1850)

P/T = constant

(when V is constant)

T

P

(1876–1956)

i.e.,

Avogadro’s hypothesis:

Equal volumes of gas at thesame temperature andpressure have the samenumber of particles.

Amedeo Avogadro(1776–1856)

Avogadro’s law:

Volume of a gas isproportional to thenumber of moles of gas. n V

e.g., 22.4 L of ANY GAS at STP contains 6.02 x 1023 particles

Amedeo Avocado

Combined Gas law: merges Boyle’s, Charles’s, and Gay-Lussac’s laws into one equation.

2

22

1

11

T VP

T VP

**NOTE:

For all gas lawcalculations, use

the absolutetemperature (in K).

Ideal Gas law:

P V = n R TR = 8.314 L-kPa/mol-K = 0.08206 L-atm/mol-K

Conditions of standard temp. and pressure (STP): 0oC (273.15 K) 1 atm

Equations for gas density:

T R

P D

22

2

11

1

D T

P

D T

P

M = molar mass of gas

Other Equations and Constants

same gas; twosets of conditions