Chapter 6

 Temperature ◦ Is something hot or cold? ◦ Relative measure

 Temperature ◦ Molecules of all substances are in constant motion ◦ Depends on the kinetic energy of molecules in a substance

 Temperature ◦ Greater the temperature ◦ Greater the motion of its molecules ◦ Measure of the average kinetic energy of the molecules of a substance

 Thermometer ◦ Measuring instrument  Utilizes the physical properties of materials to accurately determine temperature ◦ Thermal expansion  Expand with increasing temperature  Contract with decreasing temperature

 Temperature scales ◦ Reference points ◦ Ice points  Freezing point of water ◦ Steam point  Boiling point of water

 Temperature scales ◦ Fahrenheit  Ice point 32   Steam point 212  ◦ Celsius  Ice point 0   Steam point 100 

 Temperature scales ◦ Kelvin  Absolute temperature scale  Zero temperature is the absolute lower limit  Absolute zero

 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 ◦ SI unit Joule (J) ◦ Common unit calorie (cal)  Heat necessary to raise one gram of pure water by one Celsius degree

 Kilocalorie ◦ Food calorie (Cal) is equal to one kilocalorie

 British thermal unit (BTU) ◦ British system unit of heat ◦ Heat necessary to raise one pound of water one Fahrenheit degree

 Nearly all matter expands when heated and contracts when cooled  Water is an important exception ◦ Expands when frozen

 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

 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

hot substance cold substance

hot substance cold substance

hot substance cold substance

hot substance cold substance

(hot) (cold)

(hot) (cold)

(hot) (cold)

What’s going to happen to the temperature of the small block?

What’s going to happen to the temperature of the large block? What’s going to happen to the temperature of the small block?

(warm)

Heat is a form of energy that flows from one object to another (warm)

(always from hot to cold) (warm)

 Heat transfer occurs in mixtures too.  Consider mixing hot and cold water

 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

Heat gained = heat lost Heat gained Heat lost mc∆T = QQ= 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?

 Phases of matter ◦ Solids ◦ Liquids ◦ Gases  Latent heat ◦ Heat associated with a phase change

 Latent heat of fusion ◦ Heat required to change solid into liquid

 Latent heat of vaporization ◦ Heat necessary to change a liquid into a gas

 Sublimation ◦ Changing directly from the solid to the gaseous phase  Deposition ◦ Changing directly from the gaseous to the solid phase

 Boiling ◦ Process by which energetic molecules escape from liquid ◦ Energy is gained from heating ◦ Increasing pressure increases the boiling point of water

 At mountain altitudes ◦ Decreased air pressure ◦ Boiling point of water lower that at sea level

 Evaporation ◦ Slow phase change of liquid to gas ◦ Major cooling mechanism  Evaporation of perspiration has a cooling effect  Energy is lost

 Evaporation ◦ Moving air promotes evaporation by carrying away water molecules ◦ Cooling effect

 Relative humidity ◦ Amount of moisture in the air ◦ Humid environment ◦ Little evaporation of perspiration ◦ Hot feeling

 Methods of heat transfer ◦ Conduction ◦ Convection ◦ Radiation

 Conduction ◦ Transfer of heat by molecular collisions ◦ Kinetic energy of molecules is transferred from one molecule

 Thermal conductivity ◦ Measure of a substance’s ability to conduct heat  Metals ◦ Good conductors  Liquids and gases ◦ Poor conductors ◦ Molecules farther apart ◦ Less collisions

 Convection ◦ Transfer of heat by the movement of a substance, or mass, from one position to another ◦ Movement of heated air or water

 Radiation ◦ Process of transferring energy by means of electromagnetic waves ◦ Dark colors absorb radiation better than light colors

 Three common phases of matter ◦ Solid ◦ Liquid ◦ Gas

 Solid ◦ Definite shape and volume ◦ Crystalline solid  Molecules arranged in a particular repeating pattern

 Heating ◦ Molecules gain kinetic energy ◦ Vibrate about their positions in the lattice ◦ Move farther apart ◦ Lattice becomes distorted

 Liquid ◦ Slight lattice structure ◦ Molecules relatively free to move ◦ Definite volume but no definite shape

 Liquid ◦ Individual molecules gain kinetic energy when heated ◦ Liquid expands as a result ◦ Gas phase  Occurs when molecules are completely free from each other

 Gas ◦ Rapidly-moving molecules ◦ Exert little or no force on another except when they collide

 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

 Kinetic theory ◦ Pressure rises as temperature increases ◦ Gases diffuse in air

 Kinetic theory ◦ A gas consists of molecules moving independently in all directions at high speeds ◦ Higher the temperature, the higher the average speed

 Ideal gas ◦ Molecules are point particles (have no size at all) ◦ Interact only by collision  Collisions exert only a tiny force on the wall

 Pressure ◦ Force per unit area, p = F/A ◦ SI unit is N/m 2 or pascal (Pa)

 Pressure ◦ Directly proportional to number of gas molecules present ◦ Directly proportional to the Kelvin temperature ◦ Inversely proportional to volume

 The ideal gas law

 Thermodynamics ◦ Dynamics of heat  Production  Flow  Conversion to work

 Heat added to a closed system ◦ Internal energy ◦ Doing work

 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

 Heat engine ◦ Converts heat into work ◦ Some input energy is lost or wasted

 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

 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

 Heat Pump ◦ Uses work input to transfer heat ◦ Low temperature to high temperature ◦ Reverse of a heat engine

 Entropy ◦ Does a process take place naturally? ◦ The entropy of an isolated system never decreases ◦ Measure of the disorder of a system

 Entropy ◦ Disorder increases as natural processes take place ◦ Total entropy of the universe increases in every natural process