Chapter 13

Gases

Kinetic-Molecular Theory of Gases

All particles are in constant motion.As temperature increases kinetic energy

?

increases

As gas particles move apart the volume ? increases

Point Masses

Gas particles are treated as a point with no volume and no mutual attraction

-this is because they’re so small compared to the distances between them.

Ideal Gases

A theoretical gas with no volume and no attraction.

A series of theories will be studied about ideal gases

-standard pressure of 101.32 kPa -standard temperature of 0°C or 273K -standard conditions are abbreviated

STP

Therefore:Kinetic theory explains properties of gases

based on a molecular view.

The assumptions are: The molecules are in continuous, random motion. A molecule has negligible volume. The forces between molecules are negligible. The average kinetic energy depends on the

temperature.

Four Gas Law Variables Are:

V = volumeP = pressureT = temperaturen = number of particles(Upper and Lower Case is important)

Behavior of Gases

CompressionExpansionDiffusion – movement of material from

high to low concentration- lighter particles diffuse faster than heavier particles

Effusion- gas escapes through a tiny opening

Gas Pressure

Pressure = force/areaSnowshoes in the snow – force is spread out over

a larger area Gas particles exert pressure as they collide with

the walls of their containerMore particles in a given space, greater pressureBarometer is tool used to measure atmospheric

pressure – mercury rises or falls

Units of pressure

SI unit is Pascal (Pa)1Pa = 1 N/m2 derived from force1atm = 760mm Hg = 760 torr = 101.3 kPa

=14.7 psi1torr = 1 mm Hg

Dalton’s Law of Partial Pressure

Total pressure of a mixture of gases is equal to the sum of all the pressures of the individual gases

Pg. 392 practice problems

Intermolecular Forces(between molecules)

Dispersion Forces – weak forces between temporary dipoles – electron cloud is in constant motion (sometimes called London Forces).

Dipole – Dipole Forces forces between permanent dipoles (polar molecules).

Hydrogen Bonds - a type of dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to a small highly electronegative atom (oxygen, nitrogen, or fluorine)

LiquidsDenser than gases.Can’t be easily compressed.Fluidity – ability to flow (gases and liquids).Viscosity – measure of the resistance to flow.

Decreases with temperature.Surface Tension – measure of the inward pull

by particles in the interior (molecules at the surface have no attractions from above to balance the attractions from below).

Liquids (continued)

Capillary Action – liquids in a narrow container form meniscus. This is caused by two forces: Cohesion – attraction between identical molecules. Adhesion – attraction between different molecules. Example – Adhesion between glass and water in a

graduated cylinder is greater than cohesion between water molecules. Therefore water rises along the inner walls of the cylinder.

SolidsDensity is greater than liquidsCrystals – orderly, geometric, 3-D structure.

Atomic Molecular Covalent Ionic Metallic

Amorphous – not arranged in regular, repeating pattern

Phase ChangesThat require energy

Melting Vaporization (Evaporation) Sublimation

That release energy Freezing Condensation Deposition