kinetic molecular theory and the the nature of fluids a model for liquids/evaporation vapor...
TRANSCRIPT
Kinetic Molecular Kinetic Molecular Theory and the the Theory and the the
Nature of FluidsNature of Fluids
A model for liquids/EvaporationA model for liquids/EvaporationVapor PressureVapor PressureBoiling PointBoiling Point
Kinetic Molecular TheoryKinetic Molecular Theory
States that that all substances are made States that that all substances are made of tiny particles (atoms and molecules) of tiny particles (atoms and molecules) that are in constant motionthat are in constant motion
The kinetic energy and motion of these The kinetic energy and motion of these particles can help us to understand the particles can help us to understand the nature of fluids and phase changesnature of fluids and phase changes
A model for Liquids and A model for Liquids and gases- Kinetic Theorygases- Kinetic Theory
Liquids and Gases have kinetic energy---allows Liquids and Gases have kinetic energy---allows flowflow
No attraction between gas particlesNo attraction between gas particles Intermolecular attraction between liquid Intermolecular attraction between liquid
particles keeps them togetherparticles keeps them together Interplay between disruptive motions of Interplay between disruptive motions of
particles in a liquid and attractions among particles in a liquid and attractions among particles determines physical properties of particles determines physical properties of the liquid.the liquid.
Phase Changes using Kinetic Theory
Solid Liquid Gas
Low KE Medium KE Highest KE
IM Forces greater than KE so substance stays together
KE Forces overcome the IM forces to escape
Density and PressureDensity and Pressure
Liquids much more dense than gas due Liquids much more dense than gas due to intermolecular attractionto intermolecular attraction
Increased pressure has little effect on Increased pressure has little effect on liquids and solids volumeliquids and solids volume
Solids and Liquids are then called Solids and Liquids are then called condensed states of mattercondensed states of matter
EvaporationEvaporation
Conversion of liquid to gas = Conversion of liquid to gas = vaporizationvaporization Most molecules don’t have enough kinetic Most molecules don’t have enough kinetic
energy to break free energy to break free When vaporization is at the surface without When vaporization is at the surface without
boiling = boiling = evaporationevaporation During evaporation only those molecules During evaporation only those molecules
with a certain minimum kinetic energy can with a certain minimum kinetic energy can escape from the surface of the liquidescape from the surface of the liquid
Further EvaporationFurther Evaporation
Some escaping particle rebound back in Some escaping particle rebound back in off of air particlesoff of air particles
Heating increases kinetic energy which Heating increases kinetic energy which increases evaporationincreases evaporation
Removal of these higher energized Removal of these higher energized particles leaves a lower average energyparticles leaves a lower average energy
THEREFORE: evaporation is a cooling THEREFORE: evaporation is a cooling processprocess
Evaporation exampleEvaporation example
Sweating uses evaporation as a cooling Sweating uses evaporation as a cooling processprocess
Liquid on your skin takes heat energyLiquid on your skin takes heat energy Liquid evaporates taking that energy with Liquid evaporates taking that energy with
itit Leaves you with a lower temperatureLeaves you with a lower temperature
Vapor PressureVapor Pressure
Vapor Pressure – measure of the force Vapor Pressure – measure of the force exerted by the gas leaving the surface of exerted by the gas leaving the surface of a liquida liquid
Over time they increase and particles Over time they increase and particles condense ---eventually return to liquid condense ---eventually return to liquid statestate
Vapor PressureVapor Pressure
In a system of constant vapor pressure, a In a system of constant vapor pressure, a dynamic equilibrium exists between dynamic equilibrium exists between vapor and liquidvapor and liquid
Equilibrium because Equilibrium because rate of evaporation = rate of condesation rate of evaporation = rate of condesation
Vapor PressureVapor Pressure
As temperature increases, vapor pressure As temperature increases, vapor pressure increasesincreases
Particles in liquid have increased kinetic Particles in liquid have increased kinetic energyenergy
More KE, able to escape surfaceMore KE, able to escape surface Collide with “walls” Collide with “walls” Vapor pressure measured with a manometerVapor pressure measured with a manometer Vapor increases, difference between levels Vapor increases, difference between levels
increasesincreases
Boiling PointBoiling Point
Rate of evaporation increases as a liquid Rate of evaporation increases as a liquid is heatedis heated
KE increases as temperature increasesKE increases as temperature increases When a liquid is heated to a When a liquid is heated to a
temperature at which particles in the temperature at which particles in the liquid have enough KE to vaporize, the liquid have enough KE to vaporize, the liquid begins to boil.liquid begins to boil.
Boiling PointBoiling Point
Boiling point- temperature at which the Boiling point- temperature at which the vapor pressure of the liquid is equal to vapor pressure of the liquid is equal to the external pressure on the liquidthe external pressure on the liquid
Not all liquids have same boiling pointNot all liquids have same boiling point Changes in altitude also affect boiling Changes in altitude also affect boiling
pointpoint
Boiling PointBoiling Point
Boiling similar to evaporationBoiling similar to evaporation Particles with most KE rise to surface and Particles with most KE rise to surface and
break freebreak free
Temperature of boiling liquid never rises Temperature of boiling liquid never rises above boiling pointabove boiling point Escaping particles take growing energy with Escaping particles take growing energy with
themthem
Boiling PointBoiling Point
Interesting fact:Interesting fact: Burn from steam more severe than a burn Burn from steam more severe than a burn
from waterfrom water Steam particles can carry more energy than Steam particles can carry more energy than
water particleswater particles Collides with skin harderCollides with skin harder
Boiling PointBoiling Point NORMAL BOILING POINT tableNORMAL BOILING POINT table
ASSESSMENTASSESSMENT
What factors determine the physical What factors determine the physical properties of liquids?properties of liquids?
ASSESSMENTASSESSMENT
Explain how evaporation lowers the Explain how evaporation lowers the temperature of a liquid.temperature of a liquid.
ASSESSMENTASSESSMENT
What is vaporization?What is vaporization?
ASSESSMENTASSESSMENT
Define vapor pressure.Define vapor pressure.
ASSESSMENTASSESSMENT
What is a normal boiling point?What is a normal boiling point?