EFFECTS OF HEAT

EFFECTS OF HEAT

Thermal Expansion Change in Temperature Phase Change

THERMAL EXPANSION

1st Effect of Heat

THERMAL EXPANSION

Addition of heat to a body may cause it to expand and shrinks when heat is removed.

The expansion of objects can be observed in solids, liquids and gases.

It is affected by several other factors.

THERMAL EXPANSION: SOLID

SOLIDS: LINEAR EXPANSION

Change in length of a solid due to a change in its temperature

Depends on three factors: original length, Li

change in temperature, ΔT type of material / coefficient of linear

expansion,

SOLIDS: LINEAR EXPANSION

Operational Definition: ΔL = Li ΔT

where: ΔL = change in length ( Lf – Li )

Li = original/initial length

ΔT = change in temperature ( Tf - Ti )

= coefficient of linear expansion

Temperature should be in °C or K, never °FUnit of : °C-1 or 1/°C read as “per degree”

COEFFICIENTS OF LINEAR EXPANSION

Material α

Aluminum 22.2

Brass 18.7

Bronze 18

Cement 10

Cobalt 12

Concrete 12

Copper 16.6

Diamond 1.18

Material αGerman

silver 18.4

Glass, hard 5.9

Gold 14.2

Granite 7.9

Iron, cast 10.4

Iron, pure 12

Lead 28

Manganese 22

Material α

Marble 9.8

Nickel 13

Platinum 9

Silicon 3

Silver 19.5

Steel 13

Tin 23.4

Titanium 8.6

APPLICATIONS OF LINEAR EXPANSIONOperational Definition: ΔL = Li ΔT

where: ΔL = change in length ( Lf – Li )

Li = original/initial length

ΔT = change in temperature ( Tf - Ti )

= coefficient of linear expansion

Note: temperatures should be in °C or KUnit of : °C-1 or K-1

THERMAL EXPANSION: LIQUID

You will do better if you keep me in a

cool dry place. *Winks*

THERMAL EXPANSION: LIQUIDS

Operational Definition: ΔV = Vi ΔT

where: ΔV = change in volume ( Vf – Vi )

Vi = original/initial volume

ΔT = change in temperature ( Tf - Ti )

= coefficient of volume expansion

Note: temperatures should be in °C or KUnit of : °C-1 or K-1

COEFFICIENTS OF VOLUMETRIC EXPANSION

Material βAcetone 1430

Alcohol, ethyl 1090

Alcohol, methyl

1180

Ammonia 2450

Chloroform 1270

Gasoline 1000

Material β

Glycerine 500

Kerosene 1000

Mercury 180

Olive oil 700

Petroleum 1000

Water 2140

THERMAL EXPANSION: GASES

Don’t inflate me too much…

especially on a hot day.

THERMAL EXPANSION: GAS

Charles’s Law : (Recall Gas Laws, Chemistry)

Vi / Vf = Ti/ Tf

Volume is directly proportional to temperature.

(at constant pressure and number of moles)

where: temperature should be in Kelvin

COEFFICIENT OF EXPANSION OF SOME MATERIALS

Material (x 10-6/°C) (x 10-6/°C)SOLIDS Aluminum 24 75 Brass 19 56 Copper 17 Concrete 12 36 Iron 12 35 Ordinary Grass 8.5 Steel 12 35 Tungsten 4.3LIQUIDS Ethyl Alcohol 1100 Gasoline 950 Glycerin 500 Mercury 180 Water 210GAS Air 3400

WORD PROBLEMS:

1. Solid. A 1.0 m long aluminum rod is heated from 30.°C to 50.°C. (a) By how much will it expand? (b) What will its final length be?

2. Liquid. 75.0mL of ethyl alcohol at 10.°C is heated to 47°C. What will its final volume be?

3. Gas. 250.0mL of oxygen is collected at 27°C at a particular pressure. What volume will the gas have at 35°C if the pressure remains the same?

TEMPERATURE CHANGE

2nd Effect of Heat

Temperature Change

When heat is added to a system, its temperature increases.

When heat is removed from a system, its temperature decreases.

Factors that affect this temperature change the type of material, C amount of material, m amount of heat added or removed, ∆Q

Temperature Change

Specific Heat Capacity (c)- refers to the quantity of heat needed to raise the

temperature of one gram of a substance by 1 °C.

Operational Definition∆Q = mc∆TWhere:∆Q is the heat required or supplied

m mass of the substancec specific heat capacity of the

substance∆T change in temperature

Specific Heat Capacity (J/kg·K)

Material CGold 129

Mercury 139.5

Tin 227

Silver 233

Copper 385

Iron 450

Steel 466

Diamond 509.1

Material C

Granite 790

Sand 835

Carbon dioxide 839

Glass 840

Concrete 880

Aluminum 897

Oxygen 918

Air 1012

Material C

Wood 1700

Steam 2080

Ice 2110

Gasoline 2220

Plastic 2302.7

Ethyl alcohol 2440

Paraffin wax 2500

Water 4181.3

REVIEW

What is heat? Heat is the transfer of energy.

What are the different modes of heat transfer? conduction, convection and radiation

Heat transfers from _______ to _______. from an area of higher temperature

EXTENDING

What happens when two objects of different temperature are made into contact? Heat will transfer from the hotter to colder

object.

What happens to the hotter object? It gets colder because it loses energy when

heat transfers from it to the colder object.

What happens to the colder object? It gets hotter because it gains energy when

heat transfers from the hotter object to itself.

EXTENDING

Will the heat transfer continue forever or will it eventually stop? If it will stop, when? Heat transfer will stop when they reach the

same temperature. This temperature is called equilibrium temperature.

At what temperature will they have thermal equilibrium? At a temperature between the initial

temperatures (not necessarily the average though)

EXTENDING

What happens when two objects of same temperature are made into contact with each other? No heat transfer will occur.

Thermal Equilibrium

When two objects of different temperature are made into contact, heat transfer will occur.

Heat transfer will continue until both have the same temperature. When this happens, the two objects are now in thermal equilibrium.

The final temperature at which heat transfer stops is called the equilibrium temperature.

PHASE CHANGE

3rd Effect of Heat

Phase Change

Latent Heat - Addition of heat does not always results to a change in temperature; this heat could instead be used in changing the phase of some materials. This heat, which cannot be measured by thermometers, is called hidden or latent heat.

There are two types of latent heat: Latent heat of Fusion Latent heat of Vaporization

Latent Heat of Fusion ( hf )

heat needed to change 1 gram of a solid substance into 1 gram of liquid w/o changing its temperature

OPERATIONAL DEFINITIONhf = Hf / m or Hf = m hf

where: hf = latent heat of fusion of material

m = mass of materialHf = heat needed to change the material from solid to liquid without

changing temperature

Latent Heat of Vaporization ( hv ) heat needed to change 1 gram of a liquid substance

into 1 gram of gas w/o changing its temperature OPERATIONAL DEFINITION

hv = Hv / m or Hv = m hv

where: hv = latent heat of vaporization of material

m = mass of materialHv = heat needed to change the material from liquid to gas without changing temperature

Example: How much heat is required to change 100. g of ice at -20oC to 120oC of steam?