The Composition of the AtmosphereThe Composition of the Atmosphere

Dry Atmosphere at Sea Level (% by Volume)Dry Atmosphere at Sea Level (% by Volume)

Nitrogen 78.084Oxygen 20.948Argon 0.934Carbon dioxide 0.033 (increasing yearly)Neon 0.00182Hydrogen 0.0010Helium0.0052Methane 0.0002*Krypton 0.0001Xenon 0.000008Carbon monoxide, ozone, ammonia, nitrogen dioxide, sulfur dioxide <0.00001* * = variable depending upon pollution

Water content in the atmosphere isvariable in actualcontexts, rangingto over 5% in hotsteamy climates to <<1% in dryarid environments.

760 mm

Hg

PressurePressure

Atmospheric pressure is measured with a barometer

If a tube is inserted into a container of mercury open to the atmosphere, the mercury will rise 760 mm up the tube (at sea level).

(at sea level)

The Gas LawsThe Gas LawsThe Pressures-Volume Relationship: Boyle’s LawThe Pressures-Volume Relationship: Boyle’s Law

• A plot of V versus P is a hyperbola.

• Similarly, a plot of V versus 1/P must be a straight line passing through the origin.

constant PV

P is inversely proportional to V (at constant T)Mathematically:

The Gas LawsThe Gas LawsThe Temperature-Volume Relationship: Charles’ LawThe Temperature-Volume Relationship: Charles’ Law

(We know that hot air balloons expand when they are heated.)

constant TV

The volume of a fixed quantity of gas at constant pressure increases as the temperature increases.Mathematically:

• A plot of V versus T is a straight line.

• When T is measured in C, the intercept on the temperature axis is -273.15C.

• We define absolute zero, 0 K = -273.15C.

V = constant nat a constant P and T

22.4 L = constant 1 moleat a 1 atm and 273 K

Kinetic-Molecular Theory (KMT)Kinetic-Molecular Theory (KMT)• Theory of moving molecules, explains gas behavior, gives us

an understanding of temperature and pressure effects on the molecular level.

• Assumptions:

(1) Gases consist of a large number of molecules in constant random motion.(2) Volume of individual gas particles is negligible compared to volume of container (point particles).(3) Intermolecular forces (forces between gas molecules) are negligible.(4) All particle collisions with walls are elastic (no loss of energy).(5) All energy and momenta conserved.

Kinetic-Molecular Theory (KMT)Kinetic-Molecular Theory (KMT)

Pressure of a gas results from the number of collisions per unit time on the walls of container. The energy of gas molecules depends only on temperature.Thus, heavier molecules move more slowly (at the same temperature).

Acids and Bases: A Brief ReviewAcids and Bases: A Brief ReviewClassical Acids:Taste sourDonate H+ (called “H-plus” or “proton”)Turn litmus redGenerally formed from H-Z, where Z = nonmetal

Classical Bases:Taste bitter and feel soapy.Donate OH- (called “O-H-minus” or “hydroxide”)Turn litmus blueGenerally formed from MOH, where M = metal

Neutralization:Acid + Base Salt + waterH-Z + MOH MZ + HOH

H+ in water is actuallyin the form of H3O+,“hydronium”

Strong acids: completely ionized in water:HCl, HNO3, H2SO4 (also HBr, HI)

Strong bases: completely ionized in water:MOH, where M = alkaliM(OH)2, where M = alkaline earth

Strong and Weak Acids and BasesStrong and Weak Acids and Bases

Weak acids: incompletely ionized in water:any acid that is not strong - acetic acid, etc.Ka is finite.

Weak bases: incompletely ionized in water:any base that is not strong – NH3, etc.Kb is finite.

The pH ScaleThe pH Scale

Battery acid

Conc. Drano