Amole 2013

THERMAL ENERGY AND TEMPERATURE

WHAT IS THERMAL ENERGY?• Energy is the ability to do work

• It is required to move or change matter in any way

• Thermal energy is the total kinetic energy of particles that make up a substance

• More kinetic energy in particles means greater thermal energy

CHECK YOUR UNDERSTANDING• Which object in the pictures below has the most

thermal energy?

WHAT IS KINETIC THEORY?• Kinetic Theory describes the behavior of

particles in relation to thermal energy

• The three main points are…– All matter is made up of atoms and/or molecules that

act as tiny particles– These particles are always in motion. Particles move

faster at higher temperatures.– At the same temperature, more-massive (heavier)

particles will move slower than less massive (lighter) particles.

WHAT IS TEMPERATURE?• A measure of the average kinetic energy of the

particles in an object

• Tells how hot or cold something is

• Thermometers are used to find this value

• Units for temperature are degrees…– Celsius– Fahrenheit– Kelvin

CHECK YOUR UNDERSTANDING• Which object in the pictures below has the

greatest temperature?

HOW DO THERMOMETERS WORK?• Most substances expand when heated

• The liquid in the thermometers (usually colored alcohol or mercury) expand as the temperature increases1. Temperature rises2. Particles in thermometer

gain energy3. Faster particles cause them to

move farther apart and up the tube

WHAT IS TEMPERATURE?• A measure of the average kinetic energy of the

particles in an object

• Tells how hot or cold something is

• Thermometers are used to find this value

• Units for temperature are degrees…– Celsius– Fahrenheit– Kelvin

TEMPERATURE HAS 3 SCALES• Fahrenheit

– Used in Unites States– Water freezes at 32˚F– Water boils at 212˚F

• Celsius– Used by most other

countries and scientists– One ˚C is 1.8 (9/5) larger

than one ˚F– Water freezes at 0˚C– Water boils at 100˚C

TEMPERATURE HAS 3 SCALES• Kelvin

– Used to express very cold temperatures

– One Kelvin is equal to the size of one °C.

– Based on absolute zero

– Absolute zero is the temperature at which all molecular motion stops (0 K)

TEMPERATURE SCALES

CHECK YOUR UNDERSTANDINGA. What is the temperature of freezing water?

1) 0°F 2) 0°C 3) 0 K

B. What is the temperature of boiling water?

1) 100°F 2) 32°F 3) 373 K

C. What is the temperature of absolute zero?

1) 0°C 2) 32°F 3) 0 K

TEMPERATURE CONVERSIONS• On the Fahrenheit scale, there are 180°F between

the freezing and boiling points and on the Celsius scale, there are 100°C.

180°F = 9°F = 1.8°F

100°C 5°C 1°C

• In the formula for the Fahrenheit temperature, adding 32 adjusts the zero point of water from 0°C to 32°F.

TF = 9/5 TC + 32

or

TF = (1.8 TC ) + 32

TEMPERATURE CONVERSIONS• TC is obtained by rearranging the equation for TF.

TF = 1.8TC + 32

• Subtract 32 from both sides.

TF - 32 = 1.8TC ( +32 - 32)

TF - 32 = 1.8TC

• Divide by 1.8 =°F - 32 = 1.8 TC

1.8 1.8

(TF - 32) = TC 1.8

TEMPERATURE CONVERSIONSThe Kelvin temperature scale

• has 100 units between the freezing and boiling points of water.

100 K = 100°C or 1 K = 1°C

• is obtained by adding 273 to the Celsius temperature.

TK = TC + 273

16

SOLVING A TEMPERATURE PROBLEM

A person with hypothermia has abody temperature of 34.8°C. What is that temperature in °F?

TF = 1.8 TC + 32

TF = 1.8 (34.8°C) + 32°

= 62.6 + 32°

= 94.6°F Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

CHECK YOUR UNDERSTANDING The normal temperature of a chickadee is 105.8°F. What

is that temperature on the Celsius scale?

Formulas:

°F = 1.8 (°C) + 32 K = °C +273

°C = (°F – 32) °C = K -273

1.8

41.0 °C

TC = (TF - 32°) 1.8

= (105.8 - 32°) 1.8

= 73.8°F = 41.0°C 1.8°

SOLUTION

CHECK YOUR UNDERSTANDINGOn a cold winter day, the temperature is –15°C.What is that temperature in °F?

Formulas:

°F = 1.8 (°C) + 32 K = °C +273

°C = (°F – 32) °C = K -273

1.8

5°F

TF = 1.8 TC + 32

TF = 1.8(–15°C) + 32°

= – 27 + 32°

= 5°F

SOLUTION

CHECK YOUR UNDERSTANDINGWhat is normal body temperature of 37°C in

Kelvins?

Formulas:

°F = 1.8 (°C) + 32 K = °C +273

°C = (°F – 32) °C = K -273

1.8

22

310. K

TK = TC + 273

= 37°C + 273

= 310. K

SOLUTION