ENERGY CHANGES

EXOTHERMIC REACTION

CHEMICAL CHANGES

ENDOTHERMIC REACTION

PHYSICAL CHANGES

1

Chemical Change Physical change

Similarities

Substances can undergo changes ..............................

Differences

New substances formed

Change in chemical composition

Reversibility

Energy needed

SIMILARITIES AND DIFFERENCES BETWEEN CHEMICALS AND PHYSICAL CHANGES

physically

Less

Yes

Yes

More

No

Easy

No

Difficult

2

• When the ………….. is heated, purple …………

is formed. • Iodine changes from ………….to ……… without

going through the ……….. state (sublimation). • When the iodine vapour…………… the cold

………….. of the watch glass, the vapour changes back into ……….. state (black crystal).

• Solid ……………. forms on the lower surface

of the watch glass.• The change of solid iodine into iodine vapour is

…………….. • This is a ………….change.

iodine vapour

solid gasliquid

touchessurface

solid

iodine

reversiblephysical

BACK 3

Water and ................ have the ...................... particles.

The differences between water and ice are in terms of the ...............................and ......................... of the particles.

Ice can easily ................... into .................. when it is ....................... Is this a reversible process ? ........................ Is energy absorbed or released ? ........................... Is new product formed ? .....................

ice same

arrangement movement

change

Absorbed

heated water

Yes

No

BACK

4

The magnesium .................... burns with a ............... flame and forms .............. ash. During the process:

- ..................... and .................... are given off.

- Magnesium combines with ...................in the air to form ………......................

- .................................. is different from ..................................,

Is this a reversible process ?........................ Is energy absorbed or released ? ........................... Is new product formed ? .....................

ribbon

heat

whitebright

light

oxygenmagnesium oxide

magnesium oxidemagnesium

magnesium oxide

No

Yes

Magnesium + oxygen ………………………. (white ash )

(grey metal)

Released

BACK

5

Iron nails ........................... when ........................ and ......................... are present.

Rusts is a ................. substance that consists of................................

Is this reversible process ? .....................

Is energy absorbed or released ? ...........................

Is new product formed ?.....................

................... + Oxygen + .................... ............................. (Rust)

rust oxygen water

brown iron oxide

Iron Water Iron oxide

No

Absorbed

Yes

BACK

6

An endothermic reaction is a reaction

which absorbs heat energy from the surroundings.

BACK

7

An exothermic reaction is a reaction which releases heat energy to the surroundings.

BACK

8

Metal + Water Hydrogen + Metal hydroxide

The reaction of metal with water will produce hydrogen gas and alkali

A.A.REACTIVITY OF METALS WITH REACTIVITY OF METALS WITH WATERWATER

9

• Sodium and calcium (very active metal) reacts very fast in cold water.

• Magnesium, aluminium and zinc (less active metal) reacts with hot water or steam.

• Non active metals such as gold and silver do not react with either water or steam.

10

Chemical equations

Sodium + Water Sodium + hydrogen hydroxide

Magnesium + Water Magnesium + hydrogen oxide

For experiment : Refer to Appendix 1

11

B. REACTIVITY OF METALS WITH B. REACTIVITY OF METALS WITH DILUTE ACIDDILUTE ACID

Some metals react with dilute acid to produce salt and hydrogen

General equation:METAL + ACID SALT + HYDROGEN

Magnesium, aluminium and zinc react with dilute acid

Copper, silver and gold do not react with dilute acid

12

2.Type of salt produced depends on the type of acid

used.

Examples:

Zinc + sulphuric acid zinc sulphate + hydrogen

Magnesium + sulphuric acid magnesium sulphate + hydrogen

Aluminium + sulphuric acid Aluminium sulphate + hydrogen

13

C. REACTIVITY OF METALS WITH OXYGENC. REACTIVITY OF METALS WITH OXYGEN

When heated in ......................, most metals react with .......................to form ...........................

General equation

The more reactive the metal, the ...........................

the flame produced.

Metal + Oxygen ...........................

airoxygen metal oxide

brighter

metal oxide

For experiment : Refer to Appendix 2 14

The reactivity of metals with oxygen depends on the reactivity series

Metal

+ Oxygen Metal oxide

+ oxygen

Zinc

Iron

Zinc oxide+ metal

Iron oxide

For experiment : Refer to Appendix 3

15

Symbol Reactivity MetalReaction with

waterReaction with

steamReaction with

acidReaction with

oxygen

MostReactive

Potassium Hydrogen gas releasedMetal hydroxides formed

Explosion ExplosionViolent reaction

Burn brightly forming oxides

Sodium

Calcium

Magnesium No reaction Hydrogen gas releasedMetal oxides formed

React fastHydrogen gas releasedMetal salts formed

Aluminium No reaction Burn if strongly heated

Zinc No reaction

Iron No reaction

Tin (Stanum) No reaction No reaction React slowlyHydrogen gas released

Metals do not burn but oxide layer formedLead No reaction No reaction

Copper No reaction No reaction No reaction

Silver No reaction No reaction No reaction No reaction

LeastReactive

Gold No reaction No reaction No reaction No reaction

Platinum No reaction No reaction No reaction No reaction

K

Na

Ca

Mg

Al

Zn

Fe

Sn

Pb

Cu

Ag

Au

Pt16

Carbon and reactivity series

• Metal compounds higher up in the reactivity series are more stable (not easily decomposed by heat).

• These metal compounds can only be decomposed by electrolysis.

• Example:Decomposition of sodium chloride by electrolysis.

17

• Compounds of metals lower down in the reactivity series are less stable and can be decompose easily by heating.

• These metal oxides can be reduced by carbon (reducing agent) into metal and carbon dioxide.

• Example:

Zinc oxide + Carbon Zinc + Carbon dioxide

18

Symbol Reactivity Reaction of metal oxides with carbon

Mg No reaction

Al No reaction

C

Zn Less active

Fe Active

Sn More active

Pb Most active

Least active

Most active

19

Energy and Energy and chemical changeschemical changes

WaterOxygenAcid

Reactivity of metals

with

Reaction of metal oxides with carbon

Extraction of metal ores by carbon

and electrolysis

20

5.4 Applying the concepts of the reactivity series

of metal

21

CONCEPTS OF REACTIVITY SERIES

• A more reactive metal can take oxygen from the oxide of other less reactive metal to form the less reactive metal and the oxide of the more reactive metal.

• Example:Aluminium + iron oxide iron + aluminium

oxideMore reactivemetal

Oxide of less reactive metal

Lessreactivemetal

Oxide of more Reactive metal

22

• A more reactive non-metal (carbon) also can take oxygen from the oxide of other less reactive metal to form the less reactive metal and carbon dioxide.

• Example:Carbon + iron oxide iron + carbon dioxide

More reactivenon-metal

Oxide of less reactive metal

Less reactive metal

23

Extraction of metalsMetal Extraction method

Potassium

ElectrolysisSodium

Calcium

Magnesium

Aluminium

Carbon

Zinc

By heating the ore with carbon

in a furnaceIron

Tin

Lead

Copper Heating the ore alone

Mercury

Silver Exist in metal form

Gold 24

1400oC

1000oC

400oC

200oC

EXTRACTION OF TIN FROM TIN ORE (CASSITERITE)

Slag is used as road surfaces

Sulphur + arsenic

Sulphur dioxide + arsenic oxide

Tin ore + carbon

Tin +Carbon dioxide

Blast furnace

Escapes out

melt

s

Liquid tin is collectedat bottom of furnace

Hot air Hot air

limestone

25

5.5. UNDERSTANDING ELECTROLYSIS

26

1 State what electrolysis is2 State what anode, cathode, anion, cation and electrolyte are3 Describe the electrolysis of an electrolyte using carbon electrodes4 Explain the uses of electrolysis in industry

5.5. UNDERSTANDING ELECTROLYSIS

27

A

anion

CathodeAnode

Cation

Electrolyte

Rheostat

Ammeter

Switch

5.5 ELECTROLYSIS

Diagram 1

28

•Electrolysis

•Electrolyte

•Electrodes

•Cathode

•Anode

•Cations

•Anions

Process of .................................... of substance using .....................

Substance that ........................... when …………… passes through.

Substance that allow electricity to.................. or ..................

an electrolyte.

The ............................... electrode

The ................................. electrode

.......................... charged ions

........................... charged ions

Meaning of Electrolysis decomposition electricity

decomposes electricity

enter leave

negative

positive

negatively

positively

Electrical energy ………………?

Worksheet 1

29

The ExperimentElectrolysis of molten lead (II) bromide

Lead

Bromine

30

31

32

2. Electrolysis of molten lead (II) bromide

Anode Cathode

The ..............................

charged ..................... ions move to

the anode

The ..............................

charged ..................... ions move to

the cathode

....................... ions

release .......................... to the anode

and form ...............................molecules

................... ions

receive .........................from the

cathode and become ........................

atom.

............. ion + .............

................molecules

................. + electron

…........atom

............. bromine atoms form one

bromine molecule

Lead metal is ............................. on

the ...................

negatively

bromide

positively

lead

Bromide

electrons

bromine

Lead

electrons

lead

Bromide

bromine

electron Lead ion

Lead

Two deposited

cathode

33

2. Electrolysis of molten copper (II) chloride

Anode Cathode

The ..............................

charged ..................... ions move to

the anode

The ..............................

charged ..................... ions move to

the cathode

....................... ions

release .......................... into the anode

and form ...............................molecules

................... ions

receive .........................from the

cathode and turn into ........................

atom.

............. ion + ..............

...............molecules

..................... + electron

…............. atom

............. chlorine atoms form one

chlorine molecule

Copper metal is .............................

on the ...................

negatively

chloride

positively

copper

Chloride

electrons

chlorine

Copper

electrons

copper

chloride

chloride

electron copper ion

copper

Two deposited

cathode

34

A. Electroplating

USES OF ELECTROLYSIS IN INDUSTRY

Objects made of iron .................. easily when exposed to air.

To ........................... iron objects from corrosion, they are……………

with a thin layer of non reactive metal such as copper.

The aims of electroplating are to make objects more .......................

and .................. to corrosion.

corrode

prevent coated

attractive

resistant

Click for experiment

35

A

• The figure shows an iron spoon being

electroplated with copper.

i) An iron spoon is used as the ........................

ii) Copper is used as the ..............

iii) The electrolyte is a solution of ......................

compound

• At the anode :

The copper dissolves

forming ............................charged copper ions.

• At the cathode:

The .................... ions receive electrons,

forming a coat of ...................... on iron spoon.

• A rheostat is used to control the current flow in

the circuit so that a ..................... and steady

current is used. This is to ensure that the coating

is .......................... and ......................

Copper as anode

Iron spoon

Copper sulphate solution

cathode

anode

copper

positively

copper

copper

small

firm even

36

NON-REACTIVE METALS SUCH AS NON-REACTIVE METALS SUCH AS

COPPER , SILVER AND GOLD COPPER , SILVER AND GOLD

ARE FOUND AS FREE ELEMENTS. ARE FOUND AS FREE ELEMENTS.

THESE METALS THESE METALS

CONTAIN IMPURITIES AND CAN BE CONTAIN IMPURITIES AND CAN BE

PURIFIED BY ELECTROLYSISPURIFIED BY ELECTROLYSIS

37

THE IMPURE METAL IS THE ANODE

THE PURE METAL OF THE SAME TYPE IS

THE CATHODE

THE ELECTROLYTE IS THE METAL SALT SOLUTION

CONSISTING OF METALLIC IONS WHICH

IS TO BE PURIFIED

IN THE PURIFICATION OF COPPER;The impure copper is used as anodeThe pure copper is used as cathodeThe electrolyte is copper sulphate solution

38

39

B. Extraction of metals

Oxygen gases

Molten aluminium

anode carbon

Cathode carbon

Bauxite + cryolite

40

Electrolysis is a process to extract metals

such as sodium, ...................... and

aluminium which are more ....................

than carbon.

Aluminium is extracted through

electrolysis from

molten ..............................

At the cathode

i) The positively charged .......................

ions are attracted to the cathode.

ii) Aluminium ions receive electrons

and become aluminium ......................

At the anode:

i) The negatively charged

..................... ions are attracted to the

anode.

ii) Oxide ions release electrons to

become ................... atoms

iii) The oxygen atom pairs together to form

… ............ gas

magnesium

bauxite

reactive

aluminium

atoms

oxide

oxygen

oxygen

DIAGRAM

B. Extraction of metals

41

A

A

Mass of

anode .................. Mass of cathode ...................

Impurities

decreases

increases

Copper sulphate solution

Anode(impure copper)

Cathode( Pure copper)

PURIFICATION

C. Purification of metals

42

The diagram shows how electrolysis is used to purify copper

• The anode is made of ……………………..

• The cathode is made of ……………………..

• The electrolyte used is ………………………..

• When electricity is passed through the electrolyte:

i) The copper anode dissolves to form …………. ions

ii) The positively charged copper ions are attracted to

the ………………………

iii) Copper ions receive electrons from the …………….

and form copper atoms which are deposited on the

…………………

iv) At the same time the …………………… settle to the bottom

impure copper

pure copper

copper sulphate solution

copper

cathode

cathode

cathode

impurities

43

ELECTROLYSIS is a process of breaking down chemical substances in aqueous solution or molten state to its constituents by using …………………..

Electrical energy ……….......... energy

G …………….EXAMPLE:

Aluminium ion + electrons Aluminium atomOxide ion Oxygen atom + electron

(At cathode):(At anode): 44

(molten aluminium oxide)

ELECTROPLATING IRON NAIL WITH COPPER

Name of process : ……………………………..

Metal M: ……………………………………...

Electrolyte,N: ………………………………..

ANODE: ………………… CATHODE: …………………….

Metal becomes……………..

Iron nail is coatedwith ……………..layer.

**To obtain a good quality:

1. Dilute ……………… should be used.

2 Use …………….. electric current.

45

PURIFICATION OF COPPER

Name of process : ……………………………..

Electrolyte,P: ………………………………..

ANODE: ………………… CATHODE: …………………….

Impure copper………….. And impurities are left at the base.

……………… metal is formed and becomes …………..

***The presence of impurities in copper will………. its electrical conductivity. Hence, copperhas to be ………………. before it is used as aconductor of electricity.

**TASK 4

46

Zinc Zinc plateplate

G

........................................................

................

........................Copper Copper

plateplate

THE PRODUCTION OF ELECTRICAL ENERGY BY A SIMPLE CELL

A simple cell consists of two

....................... and an...........................

Two electrodes made of two different

...............

The electrolyte can be a ..........................,

....................... or ...............................

The diagram shows a simple cell circuit.

In the cell,

i) .................... and copper plates are used

as .....................

ii) ................ is more reactive than copper

iii) The electrolyte used is ..............................

electrodeselectrodes electrolyteelectrolyte

salt solutionsalt solution

dilute aciddilute acid

metalsmetals

dilute alkalidilute alkali

Zinc Zinc

electrodeselectrodes

ZincZinc

copper (II) sulphate copper (II) sulphate solutionsolution

copper (II) sulphate solutioncopper (II) sulphate solution

Cont 4

Cont 3

47

EXERCISE 1• In a simple cell, the more reactive metal acts as

the ......................... terminal which gives out electron and the less reactive metals acts as the ...................... terminal.

• In this process, the zinc plate is the ................... electrode and the copper plate is the ...................... electrode.

• The .................. from the zinc atoms flow to the copper electrode through the connecting wire. Thus the .................. electrode dissolves in the electrolyte.

• At the copper electrode , ........................ ion from the electrolyte receives the electrons.

• The flow of electron from ..................electrode to ............... electrode through the connecting wire deflect the galvanometer. This proves that the process produces ........................... energy.

negativenegativepositivepositive

zinczincelectronselectrons

hydrogenhydrogen

positive positive negative negative

electrical electrical

positive positive negative negative

48

CELL AND THEIR USAGE

Type of cells Uses Advantages Disadvantages

Dry cells ..............................

...

..............................

....

..............................

.....

............................

............................

..............................

..............................

............................

............................

..............................Wet cells ..............................

....

......................................

.....

......................................

......

......................................

......

............................

............................

..............................

..............................

Alkaline

batteries

..............................

....

……………………

….

……………………

….

......................................

...

......................................

...

......................................

....

...................................

..

Mercury

Oxide

Batteries

..............................

....

..............................

....

..............................

....

……………………

…

......................................

...

......................................

...

......................................

....

......................................

....

...................................

....

...................................

....

Nickel-

Cadmium

Batteries

..............................

....

......................................

....

......................................

....

...................................

.....

Transistor radioTransistor radio

Remote controlRemote control

Alarm clockAlarm clock

LightLight

SmallSmall

PortablePortable

CheapCheap

Non-rechargeableNon-rechargeable

Not long lastingNot long lasting

Leakage may happenLeakage may happen

Used in vehiclesUsed in vehicles

RechargeableRechargeable

High voltageHigh voltage

Long-lastingLong-lasting

HeavyHeavy

ExpensiveExpensive

Acid might spillAcid might spillDistilled water need toDistilled water need to be addedbe added

RadiosRadios

TorchlightsTorchlights

Toys Toys

Large currentLarge current

Long-lastingLong-lasting

Constant voltageConstant voltage

Watches, Watches,

Calculators, Calculators,

Hearing aids Hearing aids

CamerasCameras

Non-rechargeableNon-rechargeable

Small, long-lastingSmall, long-lasting

PortablePortable

Steady voltageSteady voltage

Constant currentConstant current

Non-rechargeableNon-rechargeableExpensiveExpensive

ExpensiveExpensiveRechargeableRechargeable

Long-lastingLong-lasting

Use in electronic Use in electronic devices such asdevices such as digital cameradigital camera

ADV 5

49

5.7 LIGHT AND 5.7 LIGHT AND CHEMICAL CHEMICAL

REACTIONSREACTIONS

CLICK

HERE50

Photosensitive Chemicals

Some chemicals are .................. to light .

The chemicals will ................... when ........................ to light.

Examples of photosensitive chemicals are ....................................

and ............................................

The chemicals cannot be .................. in a glass bottle.

Hydrogen peroxide .................. + ...........

In the presence of ......................... ,hydrogen peroxide ......................

into ..................... and ..............

Silver chloride ...................... + ...............

Silver chloride decomposes into ........................... and ..........................

The chemicals are stored in an ..................... glass bottle.

sensitivesensitive

decomposedecompose exposed exposed

hydrogen peroxidehydrogen peroxide

silver nitratesilver nitrate

storedstored

waterwater oxygenoxygen

lightlight

silversilver

decomposesdecomposes

waterwater oxygenoxygen

chlorinechlorine

silversilver chlorinechlorine

opaqueopaque

51

................................ + .................................. ............................ + .............................

During photosynthesis, ...................

(green pigment) absorbs ..........................

The energy is used to ............. the .

..................... molecules into

....................... and .......................

.........................is released into the

...............................

The ........................ atoms reacts with

carbon dioxide to form .........................

.................

Photosynthesis

Oxygen is Oxygen is released into the released into the

airair

light energylight energy

Carbon dioxide Carbon dioxide is absorbed from is absorbed from the airthe air

Glucose Glucose is sent is sent to the to the whole whole plantplant

Water and Water and mineral salts mineral salts are absorbed are absorbed from the soil from the soil by the rootsby the roots

WaterWater Carbon dioxideCarbon dioxide GlucoseGlucose OxygenOxygensunlightsunlight

ChlorophyllChlorophyll

chlorophyllchlorophyll

light energylight energy

splitsplit

waterwater

hydrogenhydrogen oxygenoxygen

OxygenOxygen

airair

hydrogenhydrogen

glucoseglucose

Instructions : Students are asked to answer the questions in Worksheet 2 after discussion.

52

…………… + ……………. ……………. + ……………….

PHOTOSYNTHESIS

chlorophyllcarbondioxide oxygen glucose water

…………………

………………………….Sunlight

53

carbondioxide water oxygen glucose

Silver bromide ...................... + ............... (Grey)

Photographic paper is coated with ......................... .

When ............... falls on the paper, silver bromide

is .......................... into ........................... and ....................... .

The formation of .................... atoms on the photographic

paper causes....................... black areas on the paper.

BromineBromine

Photographic paper

silver bromidesilver bromide

decomposeddecomposed

lightlight

silversilver

brominebrominesilversilver

greyishgreyish

SilverSilver

Instructions : Students are asked to answer questions in Worksheet 3 after discussion.

54