How Fast? How Furious?


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  • Created by: Belinda
  • Created on: 01-06-11 12:40

Rates of Reaction & Collision theory

Rates of chemical reactions can be increased by:

Increasing the temp of the reaction
Increasing the surface area of the solid reactant
Increasing the concentration of one of the reactants

Chemical reactions occur when reacting paritcle collide with each other

Activation energy = the minimum amount of energy required to cause this reaction

increasing the frequency and energy of the collisions increases the rate of reaction

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A catalyst = a substance that increases the rate of reaction without being used up in the process.

different reaction require different catalysts

catalysts work by reducing the activation energy, and they provide a surface area for the molecules to attach to increasing chnaces tof the molecules colliding

They are used a lot in the industrail process e.g:

The cracking of hydrocarbons uses broken pottery
The manufacture of ammonia uses iron

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Enzymes & Temperature changes in reactions

An enzyme is a biological catalyst, They control the rate of reaction in living things

Enzymes work better under certain conditions of temperature and PH
The enzymes in human bodies work best at about 37 degrees Celsius

they assemble into particular shapes allowing reactants to be broken down, if a protein molecule is denatured by extreme temp or PH its shape is changed

Exothermic reactions are accompanied by a rise in temp. Thermal energy is released. E.g: Respiration

Endotherimic reactions are accompanied by a fall in temp. Thermal energy is taken in. E.g: Reduction of silver ions to silver in photography

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Making and breaking bonds

Energy must be supplied to break chemical bonds

Energy is released when chmia bonds are made

If more energy is needed to break old bonds than is released when new bonds are formed the reaction = Endothermic overall

If more energy is released when new bonds are made that is needed to break old bonds, the reaction = Exothermic overall

When a reversible reaction where no reactants are added and products are removed occurs thenh an equilibrium is acheived where the reactions are at exactly the same rate in both directions

Increasing the concentration means the rate of the forward reaction will increase this means higher concentration of products so reverse reaction increases, both reactions will even out creating equilibrium

Increasing temp = reverse reaction takes in extra heat meaning the forward reaction gives out more heat , both reaction even out and equilibrium is restored

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Ammonia & The Haber Process

Ammonia = alkaline gas lighter than air

A low temp, increase the yeild of ammonia but the reaction is too slow

A high pressure increases the yeild but the reaction is too expensive

A catalyst increases the rate at which equilibrium is reached but it doesn't affect the yeild of ammonia

Ammonia consists of nitrogen and hydogenchemically joined together

The conditions needed so the reaction doesn't strat to reverse:

  • Temp of 450oc - to give a good rate of production 

  • Pressure of 200 atmospheres - high pressure 'pushes' the equilibrium position from left to right
  • Iron catalyst - increases the rate at which equilibrium is reached
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Fertilisers & Balancing Ionic Compounds

Advantages of artifical fertilisers:
Cheaper than organic fertilisers
Ready-made which are specific for certain crops

High nitrate content can be harmful in drinking water
Nitrates can leak into lakes and cause Eutrophication

Advantages of organic fertilisers:
Environmentally friendly

More needed due to low nitrogen content
Vary in efficency due to unreliabillity of their microorganism content
Need to be converted to an organic form by microorganisms before use
Messy to handle

Balance the number of electrons in a compound rather the number of atoms

Chose the lowest common multiple of the number of electrons in both ions

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