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Rate of Reaction
Is the change in concentration of a reactant or product per unit time.

Rate= change in concentration/time

Units: moldm-3s-1

Rate is fastest at the start of a reaction since each reactant has its greatest

Rate slows down as the reaction proceeds since the concentration of…

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Calculating initial rates of reaction
Is done by measuring the concentration of a reactant over a period of time. The
results obtained are plotted to give a graph. To find the initial rate, it is necessary
to find the initial slope (gradient) of the line. The graph will always be…

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Collision Theory
Reactions occur by molecules colliding. However only a small fraction of these
collisions lead to a reaction. For a collision to be effective molecules must collide
in the correct orientation and must have sufficient energy. The minimum energy
needed is called the activation energy.

Energy Profiles

The activation…

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Effect of Concentration (pressure) on reaction rates
If the concentration of the reactant increases, the reaction rate increases. There
are more molecules in the same volume so there is a greater chance of collision,
and therefore a greater chance that there will be more collisions with energy
greater than the…

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A catalyst increases the rate of a chemical reaction without being used up. A
catalyst does take part in the reaction but is unchanged and can be recovered
at the end.
A catalyst lowers the activation energy of a reaction by providing an alternative
route for the reaction.


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A heterogeneous catalyst is in a different phase from the reactants, i.e. a different form
(solid, liquid, gas.) Many industrially heterogeneous catalysts are transition metals, and
are used to absorb gases onto the metal surface and react. The larger the surface area
the better the catalyst. Examples are iron…


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