chapter 6. temperature ◦ is something hot or cold? ◦ relative measure
TRANSCRIPT
Temperature And Heat
Chapter 6
Temperature◦ Is something hot or cold?◦ Relative measure
Temperature
Temperature◦ Molecules of all substances are in constant motion◦ Depends on the kinetic energy of molecules in a
substance
Temperature
Temperature◦ Greater the temperature◦ Greater the motion of its molecules◦ Measure of the average kinetic energy of the
molecules of a substance
Temperature
Thermometer◦ Measuring instrument
Utilizes the physical properties of materials to accurately determine temperature
◦ Thermal expansion Expand with increasing temperature Contract with decreasing temperature
Temperature
Temperature scales◦ Reference points◦ Ice points
Freezing point of water◦ Steam point
Boiling point of water
Temperature
Temperature scales◦ Fahrenheit
Ice point 32 Steam point 212
◦ Celsius Ice point 0 Steam point 100
Temperature
Temperature scales◦ Kelvin
Absolute temperature scale Zero temperature is the absolute lower limit Absolute zero
Temperature
Heat◦ Flows from higher to lower temperature◦ Energy in transit because of a temperature difference◦ When heat is added to a body, internal energy
increases
Heat
Heat◦ SI unit Joule (J)◦ Common unit calorie (cal)
Heat necessary to raise one gram of pure water by one Celsius degree
Heat
Kilocalorie◦ Food calorie (Cal) is equal to one kilocalorie
Heat
British thermal unit (BTU)◦ British system unit of heat◦ Heat necessary to raise one pound of water one
Fahrenheit degree
Heat
Nearly all matter expands when heated and contracts when cooled
Water is an important exception◦ Expands when frozen
Heat
Specific heat◦ Heat necessary to raise the temperature of one
kilogram of a substance one Celsius degree◦ Specific to a particular substance◦ Greater the specific heat◦ Greater its capacity for heat
Specific Heat And Latent Heat
Recall: heat will flow from Hot to Cold ie: from high heat content to low heat
content Until they reach thermal equilibrium
Thermal Equilibrium Heat energy lost = heat energy gained
Specific Heat - Mixtures
hot substance coldsubstance
hot substance coldsubstance
hot substance coldsubstance
hot substance coldsubstance
(hot)
(cold)
(hot)
(cold)
(hot)
(cold)
What’s going to happento the temperatureof the small block?
What’s going to happento the temperatureof the large block?
What’s going to happento the temperatureof the small block?
(warm)
(warm)
(warm)
(warm)
(warm)
(warm)
(warm)
(warm)
Heat is a form ofenergy
that flowsfrom one object
to another(warm)
(warm)
(always fromhot to cold)
(warm)
(warm)
Heat transfer occurs in mixtures too. Consider mixing hot and cold water
Specific Heat – Mixtures
By mixing together, the energy from one is gained by the other.
The result is an increase in T for one and a decrease for the other
Specific Heat – Mixtures
Heat gained = heat lost
Specific Heat – Mixtures
Heat gained Heat lost
mc∆T = Q Q= mc∆T
mc∆T = mc∆T
Practice 500. g of water at 35 ºC is added to 400. g
of water at 85 ºC. What is the temperature of the resulting mixture once equilibrium has been reached?
Specific Heat –Mixtures
Phases of matter◦ Solids◦ Liquids◦ Gases
Latent heat◦ Heat associated with a phase change
Specific Heat And Latent Heat
Latent heat of fusion◦ Heat required to change solid into liquid
Specific Heat And Latent Heat
Latent heat of vaporization◦ Heat necessary to change a liquid into a gas
Specific Heat And Latent Heat
Sublimation◦ Changing directly from the solid to the gaseous phase
Deposition◦ Changing directly from the gaseous to the solid phase
Specific Heat And Latent Heat
Boiling◦ Process by which energetic molecules escape from
liquid◦ Energy is gained from heating◦ Increasing pressure increases the boiling point of
water
Specific Heat And Latent Heat
At mountain altitudes◦ Decreased air pressure◦ Boiling point of water lower that at sea level
Specific Heat And Latent Heat
Evaporation◦ Slow phase change of liquid to gas◦ Major cooling mechanism
Evaporation of perspiration has a cooling effect Energy is lost
Specific Heat And Latent Heat
Evaporation◦ Moving air promotes evaporation by carrying away
water molecules◦ Cooling effect
Specific Heat And Latent Heat
Relative humidity◦ Amount of moisture in the air◦ Humid environment◦ Little evaporation of perspiration◦ Hot feeling
Specific Heat And Latent Heat
Methods of heat transfer◦ Conduction◦ Convection◦ Radiation
Heat Transfer
Conduction◦ Transfer of heat by molecular collisions◦ Kinetic energy of molecules is transferred from one
molecule
Heat Transfer
Thermal conductivity◦ Measure of a substance’s ability to conduct heat
Metals◦ Good conductors
Liquids and gases◦ Poor conductors◦ Molecules farther apart◦ Less collisions
Heat Transfer
Convection◦ Transfer of heat by the movement of a substance, or
mass, from one position to another◦ Movement of heated air or water
Heat Transfer
Radiation◦ Process of transferring energy by means of
electromagnetic waves◦ Dark colors absorb radiation better than light colors
Heat Transfer
Three common phases of matter◦ Solid◦ Liquid◦ Gas
Phases Of Matter
Solid◦ Definite shape and volume◦ Crystalline solid
Molecules arranged in a particular repeating pattern
Phases Of Matter
Heating◦ Molecules gain kinetic energy◦ Vibrate about their positions in the lattice◦ Move farther apart◦ Lattice becomes distorted
Phases Of Matter
Liquid◦ Slight lattice structure◦ Molecules relatively free to move◦ Definite volume but no definite shape
Phases Of Matter
Liquid◦ Individual molecules gain kinetic energy when heated◦ Liquid expands as a result◦ Gas phase
Occurs when molecules are completely free from each other
Phases Of Matter
Gas◦ Rapidly-moving molecules◦ Exert little or no force on another except when they
collide
Phases Of Matter
Continued heating of a gas◦ Molecules and atoms ripped apart by collisions with
one another Plasma
◦ Hot gas of electrically charged particles◦ Ionosphere◦ Lightning strikes◦ Neon and fluorescent lamps
Phases Of Matter
Kinetic theory◦ Pressure rises as temperature increases◦ Gases diffuse in air
The Kinetic Energy Of Gases
Kinetic theory◦ A gas consists of molecules moving independently in
all directions at high speeds◦ Higher the temperature, the higher the average speed
The Kinetic Energy Of Gases
Ideal gas◦ Molecules are point particles (have no size at all)◦ Interact only by collision
Collisions exert only a tiny force on the wall
The Kinetic Energy Of Gases
Pressure◦ Force per unit area, p = F/A◦ SI unit is N/m2 or pascal (Pa)
The Kinetic Energy Of Gases
Pressure◦ Directly proportional to number of gas molecules
present◦ Directly proportional to the Kelvin temperature◦ Inversely proportional to volume
The Kinetic Energy Of Gases
The ideal gas law
The Kinetic Energy Of Gases
Thermodynamics◦ Dynamics of heat
Production Flow Conversion to work
Thermodynamics
Heat added to a closed system◦ Internal energy◦ Doing work
Thermodynamics
First law of thermodynamics◦ Positive heat values (heat is added to the system)◦ Positive work values (work done by the system)◦ Negative values indicate the opposite
Thermodynamics
Heat engine◦ Converts heat into work◦ Some input energy is lost or wasted
Thermodynamics
Second law of thermodynamics◦ Impossible for heat to flow spontaneously from a
colder body to a hotter body◦ No heat engine operating in a cycle can convert
thermal energy completely into work
Thermodynamics
Third law of thermodynamics◦ It is impossible to attain a temperature of absolute
zero◦ Would require all of the heat to be taken from an
object
Thermodynamics
Heat Pump◦ Uses work input to transfer heat◦ Low temperature to high temperature◦ Reverse of a heat engine
Thermodynamics
Entropy◦ Does a process take place naturally?◦ The entropy of an isolated system never decreases◦ Measure of the disorder of a system
Thermodynamics
Entropy◦ Disorder increases as natural processes take place◦ Total entropy of the universe increases in every
natural process
Thermodynamics