Heat EnergyESCI 215

Chapter 5

Temperature Scales

In 1714 a German-Dutch scientist named Gabriel Fahrenheit developed the first scale to be used frequently◦ Scale included: boiling, freezing, and zero points◦ He selected an arbitrary “zero” point (32°F) so

that winter temperatures would still read as positive values

◦ He selected the boiling point to be represented by 212°F, which was 180 degrees above the boiling point

Historical Background: Fahrenheit Scale

In 1742, Anders Celsius, a Swedish astronomer invented the Celsius scale

Temperature scale with:◦ Freezing point of water is the zero point (0°C)

100 degrees between the freezing and boiling points

Works well with decimal systems, so was easy for scientists to use

Historical Background:Centigrade (or Celsius) Scale

Lord Kelvin of England developed this scale Absolute zero = the lowest possible

temperature (0K) There are 273 degrees between absolute

zero and the freezing point (273K) There are 100 degrees between the freezing

and boiling points (373K) Using 0K to represent absolute zero meant

that no temperature could go below “zero” using this scale

Historical background:Kelvin Scale

Heat and temperature are different◦ Temperature scales measure temperature (not

heat)◦ Event 5-A shows the difference between

temperature and heat The nail and bolt have the same temperature, but

the bolt has more temperature See diagram page 72

Temperature – how hot or cold something; measured in degrees (F, C, K)

Heat – a quantity of energy something has

Heat and Temperature

Measuring Heat and Temperature Heat

◦ The energy a substance has due to motion of its molecules Increased heat = increased molecular motion Decreased heat = decreased molecular motion

◦ Absolute zero = the point where all molecular motion stops and a substance has no heat Scientists have never been able to get a substance

to this point Heat is measured in calories, British thermal

units (Btu), or joules

Calorie – amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius◦ Common measurement

Btu – heat needed to raise 1 pound of water by 1 degree Fahrenheit◦ Used sometimes (i.e. furnace)

Joule –work done by 1 newton of force or weight moving a body through 1 meter◦ Used by scientists

Calories, Btu, Joules

1 gram of ice at 0°C or 1 gram of water at 0°C◦ Water

1 gram of water at 100°C or 1 gram of steam at 100°C◦ Steam

Why?◦ When matter changes from a state of slower

molecular movement to a state of higher molecular movement, heat is required

Change from solid to liquid requires heat Heat is needed to melt ice or to change water to

steam Heat of fusion and heat of vaporization are needed

Which Contains More Heat?

1 calorie of heat increases temperature of 1 gram of ice by 1 degree

If ice is -10C:◦ How many calories are needed to get to 0C?

10 calories melting point - but more heat is needed to change state

Heat of Fusion - change of state from solid to liquid takes 80 calories

How many calories are needed to get to 100C? 100 calories Vaporization point – but more heat is needed to change

state Heat of Vaporization – change of state from liquid to gas

takes 540 calories

Heat of Fusion and Vaporization

Heat of Fusion and Vaporization

Figure 5.3 page 74 in Text

Where does the heat come from to change the state of matter?◦ It can come from anywhere

Air Your body Stove Hot plate

◦ When you hold an ice cube, heat is taken from your hand and used to melt the ice – leaving your hand feeling cold

◦ When you step out of a shower, heat is taken from your body and used to turn water into steam – leaving you feeling cool

Heat of Fusion and Vaporization

Event 5-B shows that there is no temperature change unless there is a change in the amount of heat present

Event 5-C demonstrates that heat of fusion is what causes the ice to melt by taking heat from the salt and using it to melt the ice◦ This causes the temperature of the salt water to

drop below freezing◦ This cooled water evaporates and forms frost on

the beaker

Heat of Fusion and Vaporization

There are many sources of heat Grouped into 4 categories:

Sources of Heat

Mechanical Chemical Electrical Nuclear

Friction Rearranging molecules

Lights Sun and stars

Bending Flame Toasters Atomic fission

Hammering Water and plaster

Heaters Atomic fusion

Pressure Sulfuric acid and sugar

Stoves Nuclear power reactor

Table 5.2 page 77 of text

Event 5-D Shake heat into a Bottle◦ Demonstrates a mechanical source of heat◦ Sand hits top and bottom of bottle and this friction

causes heat◦ Insulation around bottle is to make sure that the

heat is not coming from your hands Event 5-E Wire Heater

◦ Demonstrates a mechanical source of heat◦ Bending the wire causes heat to build at the bend

Some nails have adhesive on the shaft. This adhesive does not do anything at room temperature, but it melts when nailed into wood. Why?

Sources of Heat

Conduction Convection Radiation

Definition Transfer of heat from one molecule to another

Transfer of heat by movement of fluids

Transfer of energy by waves through space

Examples Silver spoonClothesIronCookware

Winds (weather)Chimney draftBoiling water

Sun’s heatHeat lampElectric heater

Heat Travels in 3 Ways:

Table 5.3 page 79 in text

Transfer of heat from 1 molecule to another Event 5-G Ice Preservation Race

◦ Purpose – learn about movement of heat by conduction Could be used after learning about conduction to show their

understanding of the concept Could be used before learning about conduction to have them

explore ways to slow heat transfer◦ 2 important rules:

No refrigerators, ice, or outdoors Do not let ice touch anything that will soak up water – water

needs to be measured to find the winner

◦ Best results achieved when: Size of container is small – reduces the area to be protected

from heat Conductivity is decreased – tin conducts heat well so need to

insulate the ice cube from the tin

Conduction

Good conductors◦ Metals are usually the best conductors of heat

(especially copper, silver, aluminum) Poor conductors

◦ Called insulators◦ Glass, paper, wood, plastic rubber

Event 5-H Two toned paper shows the effects of good and poor conductors◦ Wood is a poor conductor of heat so the paper scorches

more than copper which conducts the heat away Event 5-I Candle Snuffer shows a good conductor

◦ The candle goes out because the copper carries the heat away from the candle, not because of oxygen loss

Conduction

Transfer of heat by movement of fluids (gas or liquid)

Convection current - Liquids expand and become lighter when heated

Event 5-J The Mixed-Up Bottles shows a convection current ◦ Hot water is less dense and rises◦ Cold water is denser and sinks

Event 5-K The Circling Sawdust shows the movement of water

Convection

Figure 3.7 page 80 in text

Event 5-L Does Air Move In or Out shows the convection currents in air◦ One window is open on the bottom and another is

open at the top to show the air movement in the room Cold air enters the room through the lower opening

and hot air leaves the room through the higher opening

Event 5-M Convection Tester #1 shows that air rises when heated◦ Air is heated by the bulb and rises, causing the

coil to spin (see figure 5.9 on page 81)

Convection

Energy travels, at the speed of sound, from a source to an object; it travels through space◦ Ex: heat from the sun

This energy is only converted to heat when it hits a non-transparent object◦ On a cold day the sun’s light heats up a window sill,

but the window’s glass is still cold Substances vary in their ability to reflect and

absorb radiation◦ Event 5-N Which is the “warmer” colour? and Event 5-

O Hot Car show that black absorbs heat well and white reflects most of the heat energy that hits it

Radiation

All objects whose temperature is above absolute zero radiate (give off) some heat◦ The temperature must be very hot before we can feel

it Event 5-P Heat from Light shows the radiation

that a light bulb gives off◦ The heat below the light bulb is from radiation◦ The heat above the light bulb is from radiation and

convection If you had a fire in a fireplace, where would

you feel the radiant heat? Where would you feel the convection heat?

Radiation

Almost all substances expand when heated and contract when cooled◦ Index of expansion - the amount of expansion

or contraction ◦ When heated, molecules vibrate more and take

up more space Water is an exception

◦ It expands and contracts like other substances only when it is above 4°C

◦ Below 4°C it expands when cooled◦ This allows ice to form on top of water instead of

at the bottom

Expansion and Contraction

Interesting facts:◦ Sears Tower in Chicago is about 15 centimeters

taller on a hot summer day than on a cold winter day

◦ A 2km bridge can expand and contract about 1m between summer and winter

◦ Concrete highways and sidewalks have separation or joints to allow them to expand and contract without breaking

Expansion and Contraction

Event 5-Q Dancing Dimes shows how air expands when heated, rises up and pushes past the coin◦ When will the coin stop “dancing”?

When the air inside the bottle reaches room temperature

Note: the coin must have an airtight seal – wet the rim on the bottle with water

Event 5-R Jumping Juice (see safety note)◦ Hot water on outside of beaker causes the

coloured water to rise in the tube. Why?◦ Cold water on the outside of beaker causes the

coloured water to drop in the tube. Why?

Expansion and Contraction

Event 5-S The Sagging Solid shows that different metals have different expansion rates◦ Metal strip is bimetal (iron side and brass side)◦ The metal that expands more will be on the

outside of the curve◦ Which metal expands more?

Similar to 2 humans running a track. The outer lane is longer, so the runner has to run farther and faster to keep up with the runner in the inner lane

Expansion and Contraction

Event 5-T Expansion Meter shows how heat causes metal to expand◦ What happens to the weight as the wire is

heated?

Expansion and Contraction

Fig 5.12 page 85 in text

See Safety

Caution

Event 5-U Expansion of Gases shows how much air expands when heated◦ Air expands as it heats, rises and travels along

the tube and into the inverted bottle

Expansion and Contraction

Fig 5.13 page 86 in text

Fire is a chemical source of energy It releases energy by rearranging the atoms

of the object that is burning◦ A candle is a hydrocarbon – made of hydrogen (H)

and carbon (C) atoms◦ When it burns, oxygen (O) is bonded with the

hydrogen and carbon atoms◦ Carbon dioxide (CO2) and water (H2O) are produced◦ Event 5-V Water from Fire shows how fire

releases water Hydrogen atoms of candle combine with oxygen

atoms in air to produce water which condenses on the cold glass

Fire

Fire Triangle – the 3 things fire needs in order to burn:

1. Fuel2. Oxygen3. Kindling temperature – the temperature that

something will ignite at (different for different materials)

Fire will go out when 1 of these 3 things is missing

Fire is a form of rapid oxidation because it uses oxygen quickly

Fire

Event 5-W Boil Water in a Paper Cup shows how flame is extinguished when the kindling temperature is missing◦ The water in the paper cup takes the heat away

from the paper quickly, so the paper never reaches the kindling temperature

◦ The paper cup never burns, but the water boils

◦ Caution: Do not use plastic or Styrofoam cups. Why? Plastic will melt Styrofoam is a good insulator so water cannot take

the heat away fast enough and the styrofoam will burn, releasing fumes

Fire

Event 5-X Kindling Temperatures shows that different substances have different kindling temperatures◦ Some substances will ignite quickly at low

temperatures◦ Some substances will take more time and higher

temperature to ignite

◦ Caution: Do this in an area with lots of ventilation due to fumes and odours

Fire

When oxygen combines with other materials, it produces heat

Slow oxidation occurs when the heat is so little that you cannot detect it◦ When iron combines with oxygen to produce rust, it

produces heat that is not noticeable Event 5-Y Heat from Grass is a demonstration of

slow oxidation◦ Heat is produced in the moist grass as microorganisms

use the moisture to break down grass Moist grass breaks down in 1-2 days Dried hay (a type of grass) has no moisture, so can

be stored by farmers in a barn for years

Slow Oxidation

Task: Groups of 2-4 discuss and explain the following

in writing:“If hot air rises, then why is it so cold in the

mountains?” Tell students to use the words: conduction,

convection and radiation in their answer Evaluation:

Assessment and Instruction