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Concentration And Reaction Rate Essay, Research Paper

How concentration affects reaction rate.The aim of this investigation is to see how the concentration of a reactant in ratio to the reactor affects the rate of a reaction. When hydrochloric acid and Thiosulphate react together sulphur is liberated this means that as the reaction goes on the solution will become yellow and will change from being transparent to translucent to opaque. The sulphur is formed as a solid but not in the usual precipitation way.

Na2 + S2 + 2HCL 2NaCl+SO2 + S2 +H2O

To time the reaction I will draw a black cross on a piece of plain paper on which the beaker of reactants will be placed (HCL and Thiosulphate). When the chemicals come into contact with each other I will start timing with a stopwatch and will stop timing when the cross is longer visible through the beaker from above.

A reaction:A chemical reaction between to chemicals can only happen if their molecules can collide into each other. Out of many collisions there will be a few successful collisions, which means that the two molecules will exchange electrons and that means that they have reacted. These molecules have to hit each other in the right direction and at the right speed; in short the rules for a ?successful collision? are specific and complex. But if the number of collisions per second increase so will the number of successful collisions increase. This means that the rate of the reaction has increased. For a reaction to occur you also need the required activation energy which means that if there isn?t enough the reaction won?t take place although catalysts can lower this.

Input Variables:Catalyst

Concentration of acid or thiosulphate

Temperature

Light

Temperature:If you increase the amount of energy in a group of molecules the reaction rate will increase. When you give energy to molecules they tend to move about a bit more. And this means that if they are moving rapidly from place to place they are going to have a lot more collisions and because they are having lots of collisions the chances are that they will have a successful collision a lot more quickly than if they weren?t.

This basically means that reaction rate is increased as temperature increases.

I believe that temperature is directly proportional to reaction rate.

As you can see the graph is partly true to the above statement but gradually starts to curve off, this is because at a point the intense temperature will start to boil the liquids which means they will start to evaporate and concentration will be affected.

Catalyst: Activation energy is usually the amount of energy required to start a chemical reaction. A catalyst is a substance able to increase reaction rate whilst itself undergoes no change is mass or chemical composition. It does this by offering an alternative route for the reaction by lowering activation energy.

The result is that a greater proportion of the unsuccessful collisions become successful collisions because they can meet the lower energy requirement.

So there is an increase of ?successful collisions? and the rate increases without increases in temperature.

In some cases this can mean a lower temperature can be employed. An example could be hydrogen peroxide and catalase, catalase helps breakdown hydrogen peroxide into water and oxygen.

Concentration:Concentration of a reactant affects reaction rate because there are more frequent successful collisions.

Assume a person has two chemicals x and y, which react when put together.

If all input variables remained constant apart from concentration then fastest reaction rate possible would be to mix (in equal quantities which means 1 mole of x reacts with 1 mole of y) x and y together in their purest forms. This is because every time an x molecule collides into a molecule it has a 50% chance of it being a y molecule. But if you removed half of y and replaced it with a neutral chemical such as z the chances of a x molecule bumping into a foreign molecule decreases from 50% to about 25%.

This means that as concentration of y decreases so does reaction rate. This could be true for x. The same theory applies with HCL acid and Thiosulphate, so as thiosulphate concentration increases so will reaction rate. I believe that if you plotted percentage of thiosulphate against rate of reaction you would get a straight line, which also means that I predict that they are directionally proportional to each other.

Percentage of thiosulphate reaction rate * k (k being constant such as the input variables).

As you can see only 2 molecules can react with 2 HCL molecules. But if there was less water this happen:

Now 4 molecules of Mg. The reaction would be quicker than the above because:

What happens is that water molecules tend to get in the way of collisions, so if there are more water molecules in between two chemicals those two chemicals can?t really get to each other, so really water tends to ?clog up? the collisions like sawdust may clog up machinery.

Light:I am not sure if light does affect the rate of reaction in this case but it may be absorbed as heat in which case it could quicken reaction rate. Light tends to affect experiments that involve salts such as silver nitrate. In some cases it helps to lower activation energy like a catalyst. But light intensity can be absorbed as heat so as light intensity increases so does temperature, and temperature does affect reaction rate so through ?out the entire experiment I will treat light as an input variable to be controlled. See temperature as to how heat affects reaction rate.

Output variable:The best way to measure the rate of reaction is by taking advantage of the sulphur being produced. Because the reaction liberates sulphur the solution goes form

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