chapter 5 energy and chemical changes form 4

8/4/2019 chapter 5 energy and chemical changes form 4

1/29

ENERGY AND CHEMICAL

CHANGES


2/29

OBJECTIVES

Understand physical & chemical changes

Analyse heat changes in chemical reaction

Synthesize the reactivity series of metals and apply itsconcepts

Understand electrolysis

Understand the production of electrical energy by asimple cell

Understand chemical reactions that occur in the

presence of lightAppreciate the innovative efforts in the design ofequipments using chemical reactions as sources ofenergy.


3/29

PHYSICAL & CHEMICAL CHANGES


4/29

PHYSICAL CHANGES

DEFINITION

A CHANGE THAT ALTERS

THE FORM OF A MATERIALBUT DOES NOT CONVERT

THE MATERIAL INTO NEWSUBSTANCE


5/29

CIRI-CIRI / PROPERTIES

Chemical composition of materials produced

remains the same.

Colour remains the same

Its shape can be change again to its original

form.

Involves little/no change in energy


6/29

Example of physical changes

Melting of ice

heat

Ice

waterice only change its state from solid to liquid.

It can be change to its original form by

freezing


7/29

Evaporation of water

heatwater water vapour

The water has change from liquid to gasIt can be change again to liquid by

condensation


8/29

Dissolving a substance

dissolvesSugar + water sugar solution

No new substance is formed


9/29

Crystallisation

Hot saturated NaCl solution cool down and

produced NaCl crystals.

No new substance is formed.


10/29

Sublimation

Iodine crystals + heat sublimed iodineIodine has changed from crystals to powder

Freezing

cold

Water ice

Water change from liquid to solid


11/29

CHEMICAL CHANGES

DEFINITION

A CHANGE IN MATTER

THAT PRODUCES ONE

OR MORE NEWSUBSTANCE


12/29

CIRI-CIRI/ PROPERTIES

Chemical properties & composition of new

substance different from original

Reactants (bhn t/bls) changes in colour

Involves absorption or release of heat

Light energy also produced

New substances formed usually cannot bechanged back to original material physically


13/29

Examples of chemical changes

Burning magnesium in air

burn

2Mg + O2

2MgO ( magnesium oxide)New substance is form

Has different chemical properties

Energy is released


14/29

Heating a mixture of iron and sulphur

heat

Iron + sulphur iron sulphide

New substance is formedHas different chemical properties


15/29

Mixing copper chloride solution and

sodium hydroxide solution

CuCl + NaOH COH +

NaCl

Two new substances are

formed


16/29

Physical & Chemical changes in daily

lifePhysical changes Chemical changes

Crushing onions Lighting a match stick

Boiling water Frying fish

Freezing water into ice Rusting iron gate

Dissolving salt in water Digestion of food in our body

Drying clothes Mixing slaked lime in acidic soil


17/29

Comparison between physical &

chemical changesPhysical Changes Similarities Chemical changes

Both experience physical changes eg : appearance

Differences

No Formation of new

substance

yes

Same Properties & composition

of reactants (bhn t/bls) and

product( hasil t/bls)

Different

Normally yes Reversible change (

perubahan berbalik)

Normally, no

Require a little energy Energy requirement Usually require a lot energy

same Mass(jisim) reactant and

products

different


18/29

5.2 HEAT CHANGE IN CHEMICAL

REACTIONS

Occurs in most of Chemical Reaction

Involves energy transformation ( perubahantenaga)

CM can classified into two:

Exothermic & Endothermic reactions.

Heat energy absorbed from

surroundings

Heat energy released to

surroundings

To break the bond in a

compound

When the bond is formed

( to form new chemical bonds)


19/29

Exothermic reaction properties Endothermic reaction

Heat energy is released to

the surroundings

Definition Heat energy is absorbed

from the surroundings

Lose heat to surroundings Reactant ( bhn t/bls) Gain heat from

surroundings

Energy level diagram

Surrounding Temperature

raised ( increase)

Surrounding temperature

( suhu sekeliling)

Surrounding temperature

is lowered

Become hot

-container feels hot when

touch

Content in container Become cool

-Container cool when

touch


20/29

Examples of Exothermic Reaction

The burning of candle

- Candles burn heat & light are released

Reaction between magnesium & dilutesulphuric acid

- Produces a lot of heat

- Mg + H2SO4MgSO4 + H2


21/29

Examples of Endothermic reaction

Boiling water

-heat absorbed when water is boiled

Water + heat

steamMelting wax

-Wax (solid) + heat liquid wax

Dissolving Ammonium chloride in water- NH4Cl(s) + H2O(l) NH4Cl (l)


22/29

Heat Changes in Chemical Reactions In

Industries

Production of ammonia by the

Haber Process

Production of Sulphoric Acid

by the Contact process


23/29

The Reactivities Series Of Metals All metals react in water but the reactivity is

different. Some metals reacts vigorously than others

Reactivity of metals with water :

vigorously

Reactive metals + watermetal hydroxide + Hydrogen

Eg: Sodium + water sodium hydroxide + hydrogen

Less vigorously

Metal + steammetal oxide + hydrogenEg: Magnesium + steammagnesium oxide +

hydrogen

Metals like lead, copper, silver &gold dont react in water.


24/29

Reactivity of metals with acid

Reactive metals reacts with dilute acid to

produced hydrogen (g) and salt (s).

This reaction produces heat

Reactive metals reacts more vigorously.

Hydrogen collected burns with POP sound.

Salts obtained depends on metals used Eg: Mg + H2SO4MgSO4 + H2

Zn + H2SO4 ZnSO4 + H2


25/29

Reactivity of metals in Oxygen

Metals reacts with oxygen to produced metaloxide

Metal + OxygenMetal oxide

Eg :

Mg + O2MgO

Zn + O2 ZnO

Inactive metals dont react with oxygen.

Eg : gold & platinum


26/29

Reactivities series of metals.


27/29

steps

5cm3 of dilute hydrochloric acid was poured

into a test tube

A magnesium powder was added to the dilute

acid

The gas released was collected as shown in

the diagram

The gas collected was tested with a burning

wooden splinter

The above steps were repeated with the other

metals.


28/29

Volume and concentration of acid

Type of metals

Reactivity of metals


29/29

ELECTROPLATING

The electroplating process provides a

protective coating to different types of metal.

The most common use in firearms

manufacturing is chrome or nickel plating,which provide a bright finish to the metal.

Electroplating can be used on various types of

metals; the result is a thin metal coating onthe exterior of the original metal part.

Documents

chapter 5 energy and chemical changes form 4