Kinetic TheoryKinetic Theory

All matter consist of small particles. All matter consist of small particles. The molecules are in constant, The molecules are in constant,

random, rapid motion.random, rapid motion. All collisions are elastic (no net loss All collisions are elastic (no net loss

of energy).of energy).

As temperature increases, the As temperature increases, the molecules’ velocity increases, molecules’ velocity increases, increasing the pressure on the increasing the pressure on the

container.container.

Mean free pathMean free path

The average distance traveled The average distance traveled between collisionsbetween collisions

To calculate (for the curious)To calculate (for the curious)

=(average speed)x(average time =(average speed)x(average time between collisions)between collisions)An oxygen molecule will collide with other molecules 4.5 billion times per second!!

The temperature of a substance is The temperature of a substance is a measure of the average kinetic a measure of the average kinetic

energy of its particles.energy of its particles.

05

1015202530354045

100 200 300 400

temperature(K)

Kin

eti

c energ

y

Absolute zero- the temperature at which all molecular motion stops. -273.15°C

Gas PressureGas Pressure Caused by gas molecules colliding Caused by gas molecules colliding

with the sides of a container. with the sides of a container. Force per unit areaForce per unit area Units: pascal= 1Newton/mUnits: pascal= 1Newton/m22

1 atmosphere=101.325 kPa1 atmosphere=101.325 kPa

= 760 mm Hg = 760 mm Hg (torr)(torr)

How many mm Hg (or torr) is one kPa?How many mm Hg (or torr) is one kPa?

1.0 kPa x 1.0 kPa x 760 mm Hg760 mm Hg

101.325 kPa101.325 kPa

= 7.5 mm Hg= 7.5 mm Hg

Measuring PressureMeasuring Pressure

Open manometer- atmosphere exerts Open manometer- atmosphere exerts pressure on one side and gas sample pressure on one side and gas sample exerts pressure on the other side.exerts pressure on the other side. Add, if gas pressure is greater Add, if gas pressure is greater Subtract, if air pressure is greaterSubtract, if air pressure is greater

Closed manometer (barometer)- Closed manometer (barometer)- vacuum on one side, gas pressure on vacuum on one side, gas pressure on other side.other side. No addition or subtraction necessaryNo addition or subtraction necessary

States of MatterStates of Matter

StateState ShapeShape VolumVolumee

CompressiblCompressible?e?

Flows?Flows?

SolidSolid

LiquidLiquid

GasGas

DefiniteDefinite DefiniteDefiniteNoNo

IndefiniteIndefinite DefiniteDefinite NoNo

IndefiniteIndefinite IndefiniteIndefinite yesyes

NoNo

yesyes

yesyes

Vapor pressureVapor pressure The pressure produced when vapor The pressure produced when vapor

particles above a liquid collide with the particles above a liquid collide with the container walls; a dynamic equilibrium container walls; a dynamic equilibrium exists between the liquid and vapor.exists between the liquid and vapor.

Vapor pressure increases with temperature.Vapor pressure increases with temperature. A substance with A substance with weakweak intermolecular intermolecular

forces has a high vapor pressure and low forces has a high vapor pressure and low boiling point (volatile)- alcohols, ether.boiling point (volatile)- alcohols, ether.

A substance with A substance with strong strong intermolecular intermolecular forces has a low vapor pressure and high forces has a low vapor pressure and high boiling point (nonvolatile)- water, molasses, boiling point (nonvolatile)- water, molasses, glycerol.glycerol.

Phase Diagram

Critical point- above this temperature, no amount of pressure can liquefy it.

Triple point- all three phases are at equilibrium

“Normal” boiling and freezing points are those at standard pressure.

Paraffin Water