# Reaction rates and catalysts

Talking about the factors wich influence the reaction rate, also how different temperature can effect the energy within the particles. Also the role of catalysts.

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• Created by: Jasmine
• Created on: 15-04-10 11:36

## Factors influencing reaction rate

Concentration- increasing the conc in the solutions increases the frequency of collisions between the particles which increases the rate of reaction.

Pressure- increase in pressure in a gas reaction has the same effect with increase in conc, which increases the reaction rate.

Temperature - increase in temp means increase in reaction rate because of frequency of collisions and also some other reason which is described in the next card.

Surface Area - for solid and gas increases the rate of reaction. Gas - more space means come together and weaken bonds increase RR.

Catalysts - increase the reaction rate

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## Three conditions for a reaction

For a reacttion to occur, three conditions are needed:

1. A collision between the reacting particles.

2. The reacting particles must have the energy to break thier own bonds so new bonds can be formed.

3. And lastly, they must collide in orientation

The energy needed to break the existing bonds is called the activation energy for a reaction.

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## The effect of temperature

At a given temp the particles do not have 1 particular energy, but a range of energies. When the temp increases, the distribution (Maxwell-Boltzmann) of molecular energies changes.

On a distribution graph the x-axis in the kinetic energy and the y-axis measures the fraction of particles with a particular energy.

No molecules have zero energy. Each curve rises to the peak and falls away to approach the x-axis. the area under the graph if the same amount of particles is used for two curves.

At high temp - molecules with high energy and also there are many more molecules with energy higher than the activation energy - main reason temp increase the reaction rate.

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## The role of the catalysts

A CATALYST PROVIDES AN ALTERNATIVE ROUTE FOR A REACTION, WHICH HAS A LOWER ACTIVATION ENERGY.

The effect of a catalyst can be shown on a reaction profile diagram. This diagram shows how the activation energy more as it is an uncatalysed reaction. This is for an exothermic reaction - which is why the products are at a lower energy than the reactants.

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