Chemistry C2 -

Being able to speed up or slow down chemical reactions is very important - changes in temperature, concentration of solutions, surface area of solids and the presence of catalysts all affect the rates of reactions.

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The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time: 


Rate of reaction =
 

Amount of reactant used or amount of product formed
---------------------------------------------------------
Time 

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The rate of a chemical reaction increases if;


- The temperature increases  

- The concentration of dissolved reactants increases

- The pressure of gases increases

- Solid reactants are in smaller pieces (larger surface area)

- A catalyst is used

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Chemical reactions can only occur when reacting particles collide with each other with sufficient energy


The MINIMUM amount of energy particles must have to react is called the ACTIVATION ENERGY.

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Increasing the temperature increases the speed of the reacting particles so that they can collide
more frequently and more energetically. 
 

Increasing the concentration of reactants in solutions and increasing the pressure of reacting gases also increases the frequency of collisions.


These factors INCREASE the rate of reaction.

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Concentrations of solutions are given in moles per cubic decimetre (mol/dm3


Equal volumes of solutions of the same molar concentration contain the same number of moles solute

  i.e - the same number of particles.


Equal volumes of gases at the
same temperature and pressure
contain the same number of molecules.

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Catalysts change the rate of chemical reactions but
are NOT used up during the reaction. 

Different reactions need different catalysts. 

Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs. 

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