The Gas Laws AP Chemistry

e.g., gasoline vapors Basics on Gases composition of the atmosphere: ~78% N 2, ~21% O 2 properties of gases: expand to fill container compressible form 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: A  N m 2 P  N/m 2 = Pa 1 atm… = 760 mm Hg = 760 torr = kPa = bar (1 bar = 10 5 Pa) At a depth of 350 m (1150 ft), the hull pressure on a submarine is 3.4 x 10 6 Pa (36 tons/ft 2 ).

BAROMETER air pressure mercury (Hg) vacuum mercury barometer Close-up of an early mercury barometer, showing how the mercury column is supported by atmospheric pressure.

An aneroid barometer contains a small, pressure-sensitive metal box that has been evacuated of air. The box is prevented from collapsing by being connected to a spring that is also attached to the dial on the barometer. When the air pressure on the walls of the box changes, the box “flexes,” which moves the spring and the dial.

OPEN END MANOMETER CLOSED END MANOMETER air pressure Hg height difference sealed end confined gas SMALL + HEIGHT = BIGP gas = HEIGHT

The Gas Laws Boyle’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 = – o C)

Gay-Lussac’s law: Joseph Louis Gay-Lussac (1778–1850) P/T = constant (when V is constant) T P

(1876–1956) i.e., Avogadro’s hypothesis: Equal volumes of gas at the same temperature and pressure have the same number of particles. Amedeo Avogadro (1776–1856) Avogadro’s law: Volume of a gas is proportional to the number of moles of gas. e.g., 22.4 L of ANY GAS at STP contains 6.02 x particles Amedeo Avocado

Combined Gas law: merges Boyle’s, Charles’s, and Gay-Lussac’s laws into one equation. **NOTE: For all gas law calculations, use the absolute temperature (in K).

Ideal Gas law: P V = n R T R = L-kPa/mol-K = L-atm/mol-K Conditions of standard temp. and pressure (STP): 0 o C ( K)1 atm Equations for gas density:  = molar mass of gas Other Equations and Constants same gas; two sets of conditions