Mrs TeoCC

Changes in Matter can be - often reversible chemical changes physical changes - new substances are 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

- the breaking up of a substance into two or more simpler substances e.g. CuCO 3 CuO + CO 2 e.g. CaCO 3 CaO + CO 2 e.g. sugar carbon + water C 12 H 22 O C + 11 H 2 O

combination - the change in which two substances combine to form a new substance when heated e.g. iron + sulphuriron(II) sulphide Fe + SFe S

combustion - the combination of a substance with oxygen when heated to form a new substance Heat and light energy are also produced e.g. Mg + O 2 e.g. C + O 2 CO 2 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. sodium hydrogencarbonate + ethanoic acid sodium + water + carbon ethanoate dioxide Video clip - chemical_changes

Light energy can bring about changes when it falls on green plantsphotographic 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 C 6 H 12 O 6 + O 2 CO 2 + H 2 O 6 6 6

Action of Light on Photographic Film silver bromidesilver + bromine silver chloridesilver + chlorine Action of Light on Silver Chloride 2 Ag Br2 Ag + Br 2 2 Ag Cl2 Ag + Cl 2

Passing electricity through some compounds can bring about decomposition-electrolysis e.g aluminium oxidealuminium + oxygen Electrolysis of acidified water produces ______________________. hydrogen and oxygen Al 2 O 3 Al + O

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 H 2 + O 2 2 H 2 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: C 6 H 12 O 6 + O 2 CO 2 + H 2 O carbon + water dioxide light chlorophyll glucose + oxygen * 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