HEAT AND STATES OF MATTER

CHAPTER 9

TEMPERATURE AND THERMAL ENERGYSECTION 1

KINETIC THEORY OF MATTER

• ALL AROUND YOU OBJECTS ARE WARMING AND COOLING

• WHAT CAUSES THE TEMPERATURE OF AN OBJECT TO CHANGE?

• TEMPERATURE IS RELATED TO THE MOTION OF THE PARTICLES OF MATTER THAN MAKE UP AN OBJECT

• THE KINETIC THEORY OF MATTER DESCRIBES THE MOTION OF THE PARTICLES

• MATTER IS MADE UP OF ATOMS, MOLECULES, OR IONS THAT ARE CONSTANTLY IN RANDOM MOTION

• PARTICLES IN MOTION WILL HAVE KINETIC ENERGY

• WHEN PARTICLES COLLIDE THEY WILL TRANSFER KINETIC ENERGY FROM ONE PARTICLE TO ANOTHER

TEMPERATURE

• TEMPERATURE

• MEASURE OF THE AVERAGE KINETIC ENERGY OF ITS PARTICLES

• AS AVERAGE KINETIC ENERGY INCREASES, TEMPERATURE INCREASES

• TEMPERATURE SCALES

• KELVIN (K) SI UNIT

• CELSIUS (OC)

• FAHRENHEIT (OF)

TEMPERATURE CONVERSIONS

• CELSIUS TO KELVIN

• K = OC + 273

• CELSIUS TO FAHRENHEIT

• OC = (5/9)(OF – 32)

• FAHRENHEIT TO CELSIUS

• OF = (9/5) OC + 32

LET’S PRACTICE

• WHAT IS -40 O F IN DEGREES CELSIUS?

HERE’S ANOTHER ONE…

• WHAT IS THE TEMPERATURE OF 22 OC IN DEGREES FAHRENHEIT?

ONE MORE…

• WHAT IS 25 OC IN KELVIN?

THERMAL ENERGY

• NOT ONLY ARE PARTICLES IN MATTER CONSTANTLY IN MOTION, THEY ARE ATTRACTED TO ONE ANOTHER

• AS THE PARTICLES MOVE FURTHER APART, THEY GAIN POTENTIAL ENERGY

• THE SUM OF ALL THE KINETIC AND POTENTIAL ENERGY OF ALL THE PARTICLES OF AN OBJECT IS THE THERMAL ENERGY

HEAT

• HEAT

• THERMAL ENERGY THAT FLOWS FROM SOMETHING AT A HIGHER TEMPERATURE TO SOMETHING AT A LOWER TEMPERATURE

• FORM OF ENERGY

• MEASURED IN JOULES

• ALWAYS FLOWS FROM WARMER MATERIALS TO COOLER MATERIALS

SPECIFIC HEAT

• DIFFERENT OBJECTS WILL CHANGE TEMPERATURE FASTER THAN OTHERS

• AS A SUBSTANCES IS HEATED, TEMPERATURE CHANGES DEPENDS ON:

• THE AMOUNT OF THERMAL ENERGY ADDED

• NATURE OF THE SUBSTANCE

• SPECIFIC HEAT IS THE AMOUNT OF THERMAL ENERGY REQUIRED TO RAISE THE TEMPERATURE OF 1 KG OF SOME MATERIAL BY 1 OC

• MEASURED IN J/(KG OC)

Substance Specific Heat J/(kg oC)

Water 4,194

Ice 2,110

Asphalt 920

Glass 800

Iron 450

SPECIFIC HEAT OF SOME COMMON MATERIALS

CHANGES IN THERMAL ENERGY

• CHANGES IN THERMAL ENERGY ARE CALCULATED USING THE FOLLOWING EQUATION:

• Q = M X ΔT X C

• Q = CHANGE IN THERMAL ENERGY (J)

• M = MASS (KG)

• ΔT = CHANGE IN TEMPERATURE (FINAL TEMP – INITIAL TEMP)

• C = SPECIFIC HEAT OF THE SUBSTANCE

LET’S TRY IT…

• THE AIR IN A LIVING ROOM HAS A MASS OF 72 KG AN. D A SPECIFIC HEAT OF 1,010 J/(KGOC). WHAT IS THE CHANGE IN THERMAL ENERGY OF THE AIR WHEN IT WARMS FROM 20OC TO 25OC?

MEASURING SPECIFIC HEAT

• A CALORIMETER IS USED TO MEASURE SPECIFIC HEAT

• IN A CALORIMETER, A HEATED SAMPLE TRANSFERS THERMAL ENERGY TO A KNOWN MASS OF WATER.

• THE ENERGY ABSORBED BY THE WATER IS CALCULATED

• ENERGY ABSORBED = ENERGY RELEASED BY THE SAMPLE

STATES OF MATTERSECTION 2

FOUR STATES OF MATTER

• SOLID

• TIGHTLY PACKED PARTICLES VIBRATING IN SPACE

• FIXED SHAPE AND VOLUME

• LIQUID

• ATTRACTIVE FORCES ARE WEAKER THAN IN SOLID

• PARTICLES SLIDE PAST ONE ANOTHER ALLOWING FLOW

• DEFINITE VOLUME NOT SPECIFIC SHAPE

• GAS

• PARTICLES ARE FURTHER APART

• ATTRACTIVE FORCES ARE VERY WEAK

• NO DEFINITE VOLUME OR SHAPE

• PLASMA

• MOST COMMON

• CONSISTS OF POSITIVE AND NEGATIVE CHARGED PARTICLES WITH NO DEFINITE SHAPE OR VOLUME

• RESULTS FROM COLLISIONS BETWEEN MOLECULES MOVING AT HIGH SPEEDS

STATES OF MATTER

CHANGING STATES

• CHANGES IN THERMAL ENERGY CAUSE SUBSTANCES TO CHANGE FROM ONE STATE TO ANOTHER

• MELTING

• ENERGY MUST BE ADDED UNTIL PARTICLES MOVE OUT OF THEIR ORDERED ARRANGEMENT

• ENERGY REQUIRED TO CHANGE 1 KG OF A SUBSTANCE FROM A SOLID TO A LIQUID IS THE HEAT OF FUSION

• MELTING POINT IS THE TEMPERATURE WHERE AS SOLID STARTS TO MELT

CHANGING STATES

• FREEZING

• ENERGY IS RELEASED

• PARTICLES MOVE SLOWER AND THE ATTRACTION BETWEEN PARTICLES INCREASE SO THAT THEY FORM AN ORDERED ARRANGEMENT

• THE AMOUNT OF ENERGY RELEASED IS ALSO THE HEAT OF FUSION

• FREEZINGHEAT RELEASED (NEGATIVE VALUE)

• MELTINGHEAT ABSORBED (POSITIVE VALUE)

CHANGING STATE

• VAPORIZATION

• PARTICLES MOVE FASTER

• ATTRACTIVE FORCES WEAKEN

• PARTICLES NOT LONGER CLING TO EACH OTHER

• EVAPORATION OCCURS AT THE SURFACE OF THE LIQUID

• EVAPORATION CAUSES THE SURFACE OF THE LIQUID TO DECREASE

• HEAT OF VAPORIZATION IS THE AMOUNT OF ENERGY REQUIRED FOR 1 KG OF THE LIQUID TO BECOME A GAS AT BOILING POINT

CHANGING STATE

• CONDENSATION

• GAS PARTICLES SLOW DOWN

• ATTRACTIVE FORCES INCREASE

• RETURN TO LIQUID STATE

• THE AMOUNT OF ENERGY RELEASED IS ALSO THE HEAT OF VAPORIZATION

• VAPORIZATIONENERGY ABSORBED (POSITIVE VALUE)

• CONDENSATIONENERGY RELEASED (NEGATIVE VALUE)

HEATING CURVE OF A SUBSTANCE

• WHEN THE SYSTEM IS HEATED, ENERGY IS TRANSFERRED INTO IT.

• IN RESPONSE TO THE ENERGY IT RECEIVES, THE SYSTEM CHANGES, FOR EXAMPLE BY INCREASING ITS TEMPERATURE.

• A PLOT OF THE TEMPERATURE VERSUS TIME IS CALLED THE HEATING CURVE.

HEATING CURVE OF WATER

THERMAL EXPANSION

• SOLIDS, LIQUIDS, AND GASES WILL EXPAND AND CONTRACT WITH FLUCTUATIONS IN TEMPERATURE

• SLOWER MOVING PARTICLES WILL BE CLOSER TOGETHER SMALLER VOLUME

• FASTER MOVING PARTICLES WILL BE FURTHER APARTLARGER VOLUME

TRANSFERRING THERMAL ENERGYSECTION 3

WAYS TO TRANSFER THERMAL ENERGY

• CONDUCTION

• CONVECTION

• RADIATION

CONDUCTION

• THERMAL ENERGY CAN BE TRANSFERRED WHEN PARTICLES COLLIDE

• THIS TYPE OF ENERGY TRANSFER IS KNOW AS CONDUCTION

• PARTICLES CLOSEST TO THE HEAT SOURCE SPEED UP, COLLIDE WITH NEARBY SLOW MOVING PARTICLES, AND ULTIMATELY PASSING ENERGY THROUGHOUT THE SAMPLE

• REQUIRED CONTACT

CONVECTION

• CONVECTION IS THE TRANSFER OF THERMAL ENERGY BY MOVEMENT OF A FLUID OR GAS

• PARTICLES GAIN ENERGY FROM HEAT SOURCE.

• WARM AIR IS LESS DENSE AND WILL RISE.

• AS WARM AIR IS RISING, COOL AIR FROM THE SIDE REPLACES HEATED AIR CAUSING A CIRCULAR CONVECTION CURRENT.

RADIATION

• RADIATION IS THE TRANSFER OF ENERGY BY ELECTROMAGNETIC WAVES

• ENERGY TRANSFERRED BY RADIATION IS CALLED RADIANT ENERGY

• RADIATION CAN PASS THROUGH SOLIDS, LIQUIDS, AND GASES

THERMAL INSULATORS

• THERMAL INSULATORS ARE MATERIALS IN WHICH THERMAL ENERGY MOVES SLOWLY

• EXAMPLES OF THERMAL INSULATORS

• SOME PLASTICS

• WOOD

• FIBERGLASS

• AIR