Kinetic Energy, Temperature, Kinetic Energy, Temperature, Phase ChangesPhase Changes

Chapter 13 ConceptsChapter 13 Concepts

Kinetic Energy• particles have a wide range of K.E.• use the average kinetic energy of all

particles• substances in different states of matter

can have the same average K.E.– table salt, water, helium at room

temperature• the Kelvin temp. of a substance is directly

proportional to the average K.E. of the particles in a substance– 200 K has twice as much K.E. as 100 K

Temperature vs. Heat

• temperature is a measure of the average kinetic energy in a system

• heat is the energy transfer between two systems

Absolute Zero

• particles would stop moving at a very low temperature

• zero Kelvin is the temperature where motion of particles theoreticaly ceases

• closest we have come is 0.5 x 10 –9 K

Phase Changes

LIQUID

GAS SOLID

meltingvaporization**evaporation*boiling

sublimation

condensationfreezing

or solidification

= taking away heat (cooling down)= adding heat (heating up)

Vapor Pressure

• measure of the force exerted by a gas above a liquid

• dynamic equilibrium is reached when condensation equals evaporation

• an increase in temperature increases the vapor pressure of the liquid

• molecules have increased KE– more molecules will

“escape”

EvaporationEvaporation

• a type of vaporization – the conversion of a liquid to a gas or vapor

• evaporation is vaporization at the surface

• only molecules with a certain amount of KE can escape from the surface

• particles left behind have a lower KE

• thus, evaporation is a “cooling process”

• think of what happens when you sweat

Boiling Point• a type of vaporization

where the vapor pressure of liquid is equal (to the external pressure on the liquid (atmospheric pressure)

• when a liquid is heated to a temperature at which particles throughout the liquid have enough KE to vaporize

Boiling point and pressure

• BP will change due to vapor pressure

• different elevations will result in different BP

• normal BP is at STP (101.3 kPa)

Why must you cook things longer at higher elevations?

MeltingMelting Point Point

• temperature at which a solid changes into a liquid

• disruptive vibrations overcome attractive forces holding particles together

Sublimation• change from solid

directly to liquid• when solid’s vapor

pressure exceeds atmospheric pressure at room temperature

• example: iodine, dry ice, air fresheners, freeze dried coffee

Condensation

• conversion of a gas to a liquid

• molecules with lower KE go back into liquid form

Freezing or Solidification

• process in which a liquid turns into a solid when cold enough

• most liquids freeze by crystallization

• for most liquids, the freezing point and melting point are the same temperature

Phase Diagrams

• provides conditions of pressure and temperature at which a substance can exist as a solid, liquid, and vapor

• the triple point is where all three phases exist at once

Review of ConceptsReview of Concepts