PHASE CHANGESPHASE CHANGES

Kinetic TheoryKinetic Theory

Kinetic = motionKinetic = motion

Particles in a gas are Particles in a gas are considered to be hard, small considered to be hard, small spheres with an spheres with an insignificant volume.insignificant volume.

The motion of particles in a The motion of particles in a gas is rapid, constant, and gas is rapid, constant, and random.random.

All collisions All collisions between particles in between particles in a gas are perfectly a gas are perfectly elastic.elastic.

Particles in a gas Particles in a gas only interact when only interact when they collide.they collide.

Temperature (in Temperature (in kelvins, K) is directly kelvins, K) is directly proportional to the proportional to the average kinetic average kinetic energy of the energy of the particles of a particles of a substance.substance.

Objects expand when Objects expand when heated because of heated because of increased vibrational increased vibrational motion.motion.

Gas pressure is caused by the Gas pressure is caused by the collisions of particles with an object collisions of particles with an object (wall).(wall).

Atmospheric pressure results from the Atmospheric pressure results from the weight of air above an object.weight of air above an object.

Higher altitudes have less atmospheric Higher altitudes have less atmospheric pressure.pressure.

Standard atmospheric pressure is:Standard atmospheric pressure is:

1 atm = 101.3 kPa = 760 mm Hg1 atm = 101.3 kPa = 760 mm Hg

A barometer measures atmospheric A barometer measures atmospheric pressure.pressure.

LiquidsLiquids Condensed states of matter – solids Condensed states of matter – solids

and liquidsand liquids

In liquids KE is high enough for In liquids KE is high enough for molecules to flow and take the shape of molecules to flow and take the shape of their container.their container.

Intermolecular attractions give liquids a Intermolecular attractions give liquids a definite volume. definite volume.

Evaporation – changing from liquid to Evaporation – changing from liquid to vapor at the surface - cooling processvapor at the surface - cooling process

Condensation – warming processCondensation – warming process

Vapor pressure – pressure in a bubbleVapor pressure – pressure in a bubble

Boiling point – temperature at which Boiling point – temperature at which the vapor pressure equals external the vapor pressure equals external pressure on the liquidpressure on the liquid

Gas Stoichiometry

1 mol of a gas at standard temperature and pressure (STP) = 22.4 L

Volume – Volume Problems 2NO + O2 2NO2 How many liters of nitrogen dioxide are

produced when 34 L of O2 react?

22

2

2

2

2

22 NOL68

NOmol1

NOL4.22

Omol1

NOmol2

OL4.22

Omol1OL34

What cancels?

22

22 NOL68

OL1

NOL2OL34

Volume – Moles Problems 2NO + O2 2NO2 How many moles of nitrogen dioxide

are produced when 34 L of O2 react?

22

2

2

22 NOmol04.3=×

Omol1

NOmol2×

OL4.22

Omol1×OL34

Solids Phase Changes

The general properties of solids reflect the orderly arrangement and fixed locations of their particles.

Crystal - regular geometric arrangement

Allotropes - (diamond, graphite) 2 or more different molecular forms of the same element in the same physical state

Amorphous - no geometric pattern

Phase changes Sublimation - solid to vapor Vaporization - liquid to vapor

(evaporation or boiling) Solidification - liquid to solid Melting - solid to liquid

A) 0.016C, 0.61 kPa B) S, L, V C) 100C; 0C

Ch 13 Review Notes

Atmospheric pressure affects the boiling point of a liquid.

STP – standard temperature and pressure - 0C and 1 atm

1 atm = 760 mm Hg so…

Hgmm1900atm1

Hgmm760atm5.2

Absolute zero = 0 K is the temperature the motion of

particles theoretically ceases.

Triple point – conditions ( temperature & pressure) at which solid, liquid, and vapor (gas) can exist in equilibrium.

Solids are more dense than liquids and gases.

Sublimation can occur because solids have a vapor pressure.