Ch.12.chemistry in everyday life

CHEMISTRY IN EVERYDAY LIFE

CHAPTER 12(CHEMISTRY)

IN EVERYDAY LIFE WE SEE:

BIOLOGY PHYSICS CHEMISTRYCHEMICAL REACTIONS

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CHEMICAL REACTIONS IN EVERYDAY LIFE

Respiration

Combustion Burning Explosion

s caused by dust

Reactions with

oxygen

Oxygen and food

Hand warmers Rusting Metals

and air

RESPIRATION

It is the process that releases energy from glucose using oxygen (for all life processes)

Glucose + oxygen Carbon dioxide + water

COMBUSTION

It is the process that releases heat energy from fuels (in petrol and diesel engines)

Fuel + oxygen Carbon dioxide + water

BURNING

• If a flame develops during combustion the reaction is then called burning.

• During burning, energy is given out as heat, light and sound.

Fuel + oxygen Carbon dioxide + water

EXPLOSIONS CAUSED BY DUST

• Occasionally there may be a news story about an explosion in a coal mine or in a flour mill.

• Explosions in these places can be caused by coal and flour (not explosives)

• If a piece of coal is heated is burns steadily.

• If coal dust is heated it explodes.

• Coal dust explodes because it has large surface area

• This means when coal dust is hot it reacts very quickly with the oxygen in the air.

• The heat produced by this fast reaction causes the air to expand rapidly and push on everything around it with great force.

REACTIONS WITH OXYGEN• A chemical reaction in which oxygen combines

with a substance is called an oxidation reaction.

1) OXYGEN AND FOOD

• Some foods contain fats and oils.• If they are left out in the air for a few days they

may start to smell unpleasant.• This is due to the oxidation reaction which

takes place between the fats and oils and the air (food becomes rancid and inedible)

• Chemicals have been developed to slow down the oxidation of fats and oils in air (called antioxidants).

• Many foods, such as corn chips, are further protected form oxidation by the gas in their unopened bags (bags full on nitrogen)

• Some fruits contain natural antioxidants ex. Lemons and oranges.

2) HAND WARMERS• People who spend time in cold conditions

sometimes use hand warmers to keep them comfortable.

• Hand warmers are stored in sealed packages until they are needed to provide heat to the body.

• In one type of hand warmer iron is enclosed in a par of bags which are sealed to keep out the air.

• When they are needed the packet is opened and air passes through the walls of the bags.

• The oxygen in the air reacts with the iron to produce iron oxide.

• Heat produced from this reaction is spread out by other substances in the bag.

3) RUSTING• Rusting is a slow reaction which takes place

between iron, oxygen and water.

Iron + oxygen + water Rust

• When vapour from the air condenses on iron or steel (iron +carbon) it forms a film on the surface of the metal.

• Oxygen dissolves in the water and reacts with the metal to form iron oxide.

• Iron or steel continue to produce rust until they are completely corroded (damaged).

Hydrated iron oxide

• Steel girders are used to support bridges.

• Steel is also used to make many parts of cars.• If the steel is not protected it begins to rust

(weak metal)• This makes bridges unsafe.• It makes holes in care bodies and weakens the

joints that hold the car together making it unsafe to use.

FACTORS THAT SPEED UP RUSTING• Rusting speeds up if the reactants are warm.

• Salt in the water also speeds up rusting.

QUESTIONS TO REFLECT UPON• What are the reactants of rusting?

• Salt in the water speeds up rusting. Which type of transport vehicle will rust quickly?

RUST PREVENTION• Rust can be prevented by keeping oxygen and

water away from the iron or steel surface.• This can be done by painting the surface or

covering it in oil.• But, if the paint becomes chipped or the oil dries,

rust can begin to form.

• Steel can also be prevented from rusting by:

Chromium plating

(covering surface with chromium)

Tin plating(covering surface with tin)

Stainless steel(Mixing steel with nickel

and chromium to form an alloy)

4) OTHER METALS AND THE AIR

• When aluminum or zinc is exposed to the air, the metal on its surface reacts with oxygen in the air and forms oxides.

• These oxides do not flake like rust but form a protective surface on the metal.

• Zinc is used to protect iron because it is more reactive.

• If the zinc coating on galvanised iron is chipped, the oxygen reacts with the zinc instead (rust prevented)

• Zinc patina (Zinc oxide)

• Bronze patina (oxidized bronze).

• a

• Tarnished silver

• Copper verdigris (Copper carbonate)

• There are 2 types of reactions:

Exothermic reactions

(Chemical reaction in which energy is given out)

Endothermic reactions

(Chemical reactions which take heat from their surroundings)

- Burning (a candle flame)- Rusting iron- Neutralisation reactions between acids and alkalis- The reaction between water and calcium oxide

- The reaction between Ethanoic acid and sodium carbonate

- Melting ice cubes- Evaporation of water- Mixing water and

ammonium nitrate

• When trying to classify a process as exothermic or endothermic watch how the temperature of the surroundings changes.

• An exothermic process releases heat, and causes the temperature of the immediate surroundings to rise.

• An endothermic process absorbs heat and cools the surroundings.