Mrs TeoCC

Changes in Matter can be

- often reversible

chemical changes

physical changes

- new substancesare produced

- no new substances are produced

-often irreversible

Changes in matter can be brought about by

1.______________ 3.________________ energy

2.______________ 4.________________energy

mixing

heat

light

electricity

• combination• combustion• decomposition

•decomposition

- the breaking up of a substance into two or more simpler substances

e.g. CuCO3 CuO + CO2

e.g. CaCO3 CaO + CO2

e.g. sugar carbon + water

C12H22O11 12 C + 11 H2O

•combination- the change in which two substances combine to form a new substance when heated

e.g. iron + sulphur iron(II) sulphide

Fe + S Fe S

•combustion

- the combination of a substance with oxygen when heated to form a new substanceHeat and light energy are also produced

e.g. Mg + O2

e.g. C + O2 CO2

2 MgO2

Mixing of certain chemicals can also result in the production of new substances.

carbon + water (absorbed by the acid)

sugar

concentrated

sulphuric acid

e.g.

e.g.

sodium hydrogencarbonate + ethanoic acid sodium + water + carbon

ethanoate dioxide

Video clip - chemical_changes

Light energy can bring about changes when it falls on

green plants photographic films(whose leaves absorb light

energy to make ___________ in a process called

______________________)

(light decomposes the silver bromide on them into ___________ and bromine)

glucose

photosynthesis

silver

Equation for photosynthesis:

carbon + water

dioxide

light

chlorophyll

glucose + oxygen

C6H12O6 + O2 CO2 + H2O 6 6 6

Action of Light on Photographic Film

silver bromide silver + bromine

silver chloride silver + chlorine

Action of Light on Silver Chloride

2 Ag Br 2 Ag + Br2

2 Ag Cl 2 Ag + Cl2

Passing electricity through some compounds can bring about decomposition-electrolysise.g aluminium oxide aluminium + oxygen

Electrolysis of acidified water produces

______________________.hydrogen and oxygen

Al2O3 Al + O2 2 4 3

Chemical Reactions are accompanied by energy transfers with the surroundings in the form of

• heat energy

• light energy or both

Video clip - chemical_changes

During a chemical reaction,

• atoms of the reactants rearrange themselves to form new substances

involve

breaking of bonds and making of new bonds

requires energy releases energy

* The breaking of the chemical bonds between the hydrogen atoms and the oxygen atoms requires heat energy.

* The making of the new chemical bonds in the water molecules releases heat energy.

* The energy released is greater than the energy absorbed, so the the reaction is said to be exothermic.

The net result is that energy is released.

2 H2 + O2 2 H2 O

+

1. If the amount of energy released during the making of new bonds exceeds the amount of energy absorbed for the breaking bonds, energy will be released to the surroundings.

2. Such a reaction is called an exothermic reaction.

Equation for photosynthesis:

C6H12O6 + O2 CO2 + H2O

carbon + water

dioxide light

chlorophyll

glucose + oxygen

6 6 6

* The breaking of the chemical bonds in the carbon dioxide and water molecules requires energy.

* The making of the new chemical bonds in the glucose and oxygen molecules releases energy.

* The energy absorbed is greater than the energy released, so the the reaction is said to be endothermic.

The net result is that energy is absorbed..

light

chlorophyll

1. If the amount of energy absorbed for the breaking of bonds exceeds the amount of energy released during the making of new bonds, energy will be absorbed from the surroundings.

2. Such a reaction is called an endothermic reaction.

energy is released energy is absorbed

during exothermic reactions

during endothermic reactions

e.g. combustion of fuels

e.g. photosynthesis and

decomposition of silver chloride by light,

decomposition of calcium carbonate by heating

and respiration