Rates Of Reaction

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Rates Of Reaction

Rate Of Reaction is basically how much chemical reacts, or is formed, in a given time.

Rate Of Reaction formula: Amount of Reactant used up   OR   Amount of product Formed                                                       Time Taken                                Time taken 

You can alter rate of chemical reaction by: increasing temperature, using smaller peices of a reactant, increasing concentration of reactant, or adding a catalyst!

Often A Gas is produced and so is easy to measure. You can measure it using: An Upturned Cylinder, Gas Syringe, Or a Burrete 


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Collision Theory

For a chemical reaction to occur, the reactants must collide with each other

Changes that increase the number of collisions will increase the rate of reaction.

But Collision has to be hard enough to cause a reaction. This can be done by: increasing Temperature, Increasing Concentration, Increasing Pressure, Using smaller particles of a solid, Adding a Catalyst 


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How Much Change?

2x Concentration = 2x the rate of reaction

Cutting a cube of solid into 8 peices will 2x its surface area and 2x the rate.

Increasing temperature will always increase the rate of a reaction.

Different reactions need different catalysts, not all reactions can be catalysed!

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Adding Energy

Increasing Temperature will add energy in a reaction 

Adding energy speeds up a reaction BUT reactant will produce the same amount of product as you do not change concentration with Temperature.

So temperature only speeds up reaction.

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Activation Energy

To Cause a reaction Particles must collide with sufficient energy to break bonds.

The minimum energy needed for this to happened is called the ACTIVATION ENERGY 

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Concentration

Higher Concentration = more reactant particles in the same volume 

So there are more collisions per second, increasing reaction rate.

Increasing concentration does not effect energy of collisions.

Reactants are use up during a reaction and their concentration decreases, that is why a concentration graph curves.

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Two Solutions

Doubling concentration of one reactant will double the rate of the reaction.

If you double both reactants then the reaction rate will double twice, that means it will go four times as fast

It will also be a complete in a quarter of the time.

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Liquids And Gases

Liquids react with gases much faster if sprayed into tiny droplets first.

Oil-fired burners and furnaces spray in the fuel oil, so that it burns rapidly.

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Size And Surface Area

Solids only react at their surface. 

Breaking a solid into smaller pieces exposes more surface area. that provides more reactant particles to be available for collisions: the reation rate increases 

The ratio between the two surface areas shows the change in rate of reaction. for example, if you reduce particle size from 1cm(^3) to 1mm(^3)

For 1cm cube surface area: 

  • each face= 10mm x 10mm = 100mm(^2)
  • total= 6 x 100mm(^2) = 600mm(^2)

For 1mm cube surface area:

  • each face = 1mm x 1mm = 1mm(^2)
  • total 6 x 1mm(^2) = 6mm

A 1cm cube contains 1000 cubes of 1mm side length, so:

  • surface area of 1000 cubes = 6000mm(^2)
  • 6000/600 = 10, so the reaction will be ten times faster 
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