Chemical reactions
Gives out a great amount of energy – wydziela dużą ilość energii
Dependence on fossil fuels – zależność od paliw kopalnych
Combustion engine - silnik spalinowy
Bi-fuel engine – silnik dwupaliwowy
Put in place - wprowadzony
Poses its own problems - stwarza własne problemy
Stored safely – przechowywany bezpiecznie
Forcing - zmuszanie, wymuszanie, narzucanie
Reliable fuels - niezawodne paliwa
Immensely - niezmiernie
Commitment - zaangażowanie
Reap the benefits – czerpanie korzyści
Non-polluting - niezanieczyszczanie
Prospect - perspektywa
Hydrogen fuel cell car - samochody na wodorowe ogniwa paliwowe
Filling stations – stacje paliwa
Crystal lattice – sieć krystaliczna
Vast – ogromny, rozległy
Devastatingly damaging – zatrważająco szkodliwy
4.1 Chemical reactions and equations.
Interconnecting reactions – reakcje łączenia
Chemistry deals with how substances react with each other.
Physical changes:
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The substances present remain chemically the same: no new substances are formed.
Are often easy to reverse. Any mixtures produced are usually easy to separate.
Water exists under different conditions of temp. Or pressure – one form can change into another if
those conditions change.
Dissolving sugar in ethanol or water – it produces a solution, but the substances can easily be
separated again by distillation
Chemical change:
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Exothermic change – energy is given out in the form of heat and light. Example –
chemiluminescence, burning magnesium, the condensation of steam to water
Endothermic change – energy is taken in in form of heat from surrounding. Example – the addition
of concentrated sulfuric acid to water, reaction between nitrogen and oxygen.
The new substances are made during the reaction
Many reations (not all) are difficult to reverse
More exothermic than endothermic reactions.
4.2 Equations for chemical reactions.
Word equations – type of equation which links together the names of the substance that react (the
reactants) with those of the new substances formed (the products). This type gives us some information.
Balanced symbol equations:
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Law of conservation of mass – the total mass of all the products of a chemical reation is equal to
the total mass of all the reactants.
During a chemical reaction, the atoms of one element are not changed into those of another
element.
Balanced equation – the numbers of each type of atom are the same on both the reactant side and
the product side of the equation.
Writing balanced equations:
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You cannot change the fromulae of the substances themselves when balancing equations. These
are fixed by the nature of the atoms and their bonding.
4.3 Types of chemical reaction.
Synthesis reactions - (direct combination) occur where two or more substances react together to form just
one product. They are usually exothermic. There is one synthesis reaction, which is endothermic namely
photosynthesis (photochemical reaction)
Spontaneous - spontaniczny
Vigorous - energiczny
Chlorophyll – chlorofil
Decomposition reactions – have just one reactant, which breaks down to give two or more simpler
products.
Thermal decomposition – decomposition caused by heat energy.
Neutralisation reactions – involve acids. When acid react with bases or alkalis, their acidity is destroyed.
They are neutralised and a salt is produced.
Precipitation reactions – involve the formation of an insoluble product.
Precipitation – the sudden formation of solid, either when two solutions are mixed or when a gas is
bubbled into a solution.
Limewater test – badanie wody wapiennej
Displacement reactions – occurs because a more reactive element will displace a less reactive one from a
solution of one of its compounds.
The halogens can be placed in order of reactivity using displacement reactions.
Combustion – the reaction of a substance with oxygen causing the release of energy. The reaction is
exothermic and often involves a flame.
Burning – combustion in which a flame is produced.
Fuels - substances such as methane, which undergo combustion readily and give out a large amount of
energy.
Digestation – during that, food i broken down into simpler substances.
Respiration – exothermic reaction.
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If a substance gains oxygen during a reaction, it is oxidised.
If a substance loses oxygen during a reaction, it is reduced.
Reducing agent – an element or compound that will remove oxygen from other substances. The
commonest reducing agents are hydrogen, carbon and carbon monoxide.
Oxidising agent – a substance that will add oxygen to another substance. The commonest oxidising agent
are oxygen, hydrogen peroxide, potassium manganate vii and potassium dichromate vi.
Examples of oxidation reactions:
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Corrosion – if a metal is reactive, its sufrace may be attacked by air, water or other things. When
iron or steel slowly corrodes in damp air, the product is a brown, flaky rust. Rusting weakens
structures such as car bodies.
Rancidity – when the fats and oils in butter and margarine oxidised, they become rancid.
Manufactures add antioxidants to fatty foods and oils to prevent oxidation. Keeping foods in
refrigerator can slow down the oxidation process, storage in airtight containers.