topic 2 - speed of reactions chemical reactions can be fast: like this explosion

Topic 2 - Speed of Reactions


Chemical reactions can be fast:

Like this explosion


Chemical reactions can be slow:

Like the decomposition of this apple.


Chemical reactions can be very slow:

Like the rusting of iron.


We can speed up chemical reactions:

By increasing the temperature.

have more energy

move faster

collide more often

are more likely to react successfully.

When heated the particles of substances:-



By increasing the concentration.

•A more concentrated solution has more reacting particles

•Particles have a bigger chance of coming into contact and reacting.



By decreasing the particle size.

When a lump of a reacting substance is broken into smaller pieces:

• the substance can more easily come into contact with the other reactant

• material from the inside of the lump can now react not just the outside surface.


There are many examples of reactions which are affected by temperature.

• Glucose reacts more quickly with Benedict’s solution as the temperature is increased.

• Rusting of ships sunk in deep cold waters takes place very slowly.

• Decay of food speeds up when it is removed from the fridge into a higher temperature.

• Stains are more easily removed from washing at higher temperatures.


There are many examples of reactions which are affected by changing concentration.

• Clothes can be bleached more quickly using a more concentrated bleach.

• Magnesium dissolves quicker and gives off hydrogen faster in 2% acid than it does in 1% acid.

• When the amount of washing powder is less, clothes are not cleaned so effectively because the reaction is slower.


There are many examples of reactions which are affected by changing particle size.

•Chalk lumps react with acid much more slowly than chalk powder.


•Potatoes cut into smaller pieces cook more quickly than whole potatoes.

Smaller particle size speeds up reaction.


•Iron powder blown into a flame burns rapidly while an iron bar just glows.

Large surface area - quick reaction


Catalysts

• Speed up chemical reactions

• Are not used up in the reaction

• Can be recovered at the end of the reaction.

• Save energy because they allow many reactions to be carried out at a lower temperature.


Catalysts have many uses:

• Iron is used as a catalyst in the production of ammonia, an important chemical used in fertiliser production.

• Nickel is used in hydrogenation of vegetable oils. This process hardens oils to make margarine.

Note: the catalysts above are transition metals.


PlatinumPlatinum is used in catalytic converters in is used in catalytic converters in car exhausts to speed up the breakdown of car exhausts to speed up the breakdown of

harmful gases into harmless gases.harmful gases into harmless gases.


Enzymes

• are biological catalysts

• speed up reactions in living things.

• In the human body reactions have to take place at 370C and many are helped by enzymes.

• Amylase is an enzyme in our saliva which speeds up the breakdown of starch.

• Enzymes are used in the production of beer, wine, cheese and yoghurt.

topic 2 - speed of reactions chemical reactions can be fast: like this explosion

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