Reaction Rates 3 - Catalysts

Catalysts
Catalysts are chemical substances that
• increases the rate of a chemical reaction
• but it does not experience any permanent chemical change itself
• and is not used up (is not consumed).

When a catalyst is added, the rate of the reaction increases because the catalyst decreases the Activation Energy (energy barrier) making it easier for the reaction to proceed.

Catalysis is the change in the rate of a chemical reaction caused by the presence of a catalyst.

Study the graph below.
The purple line shows the energy changes with a catalyst included.
Note that the energy of the Catalysed Activated Complex is now 65kJ, much lesser than before.
The new Catalysed Activation Energy is 65 – 45 = 20kJ.
Due to this decrease in “barrier energy”, the reaction proceeds faster.

However, do notice that the Initial Energy (45kJ) and Final Energy (25kJ) is unaffected.
Hence the Heat of Reaction is unchanged. ΔH is still -20kJ

A Catalyst:
• decreases the Activation Energy
• decreases the energy of the Activated Complex
• increases the Rate of Reaction
• has no effect on the Heat of Reaction
• has no effect on the Initial and Final Chemical Potential Energies
• does not affect the yield (amount of product)
• no increase or decrease in amount
• cannot start a reaction that was not going to occur in the first place
• allows reactions to be performed at a lower temperature

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V. Gokal
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