I will be investigating how the rate of reaction changes as the concentration of a solution changes.

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Chemistry Coursework

Rates of Reaction

Aim

I will be investigating how the rate of reaction changes as the concentration of a solution changes. I will do some preliminary research and investigations, which will lead to the main part investigation where I will change, the concentration of Sodium Thiosulphate when reacting with Hydrochloric Acid (See Method). I will analyse and evaluate my results and look for relationships and trends in them, I will also be considering any anomalous data.

Scientific Information

Rates of reaction can be increased (according to the collision theory [see Collision Theory]) in four ways:

  1. Higher Temperature increases the number of collisions.

 

When the temperature is increased the colliding molecules all move faster so they are going to have more collisions. (Faster collisions increase the rate of reaction.) So more of the collisions are also more energetic and exceed the activation energy for reactions. Reactions can only happen when different particles come together. 

  1. Increase in Concentration (or Pressure) increases the number of collisions.

When there are more particles around to take part in a chemical reaction, they bump into each other more often, which make collisions between the important particles more likely. In a gas increasing the pressure means the molecules are more squashed up together so there are going to be more collisions.

  1. Increase in Surface area increases collisions. 

If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area so collisions are far more frequent. Due to more collisions the rate of reaction is greater.

4) Catalysts are important for many biochemical and industrial processes because they speed up reactions that ordinarily occur too slowly to be useful (catalysts don’t get used up them selves).  There are different opinions to the reason to why this happens:

i) A catalyst works by giving the reacting particles a surface to where they can bump into each other. This obviously increases the number of collisions.

ii) The catalyst lowers the activation energy and more collisions are successful so the rate of reaction is greater.        

Three ways to measure the speed of a reaction

The speed of reaction can be observed either by how quickly the reactions are used up or how quickly the products are forming. It’s usually easier to measure products forming. There are three different ways that he speed of reaction can be measured:

1) Precipitation

This is when the product of the reaction is a precipitation, which clouds the solution. By observing a marker through the solution it would be possible to measure how long it takes for it to disappear (I will use this in my investigation).

2) Change in mass (usually gas released)

Any reaction that produces a gas can be carried out on a mass balance, as the gas is released the mass disappearing is easily measured.

3) The volume of gas released from the solution

This involves the use of a gas syringe to measure the volume of gas given off from the reaction. The gas is collected, and then measured.

Types of Reaction:

There are two different categories a reaction can belong to, an exothermic or an endothermic. When two substances mix to form a solution, heat is either evolved or absorbed.

Exothermic- reaction, which takes energy from the surroundings.

Endothermic - reaction which transfers energy to the surroundings.

Activation Energy - activation energy, the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport. If it is high then the reaction rate will be very slow particularly in room temperature.

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Collision Theory - The Collision theory builds on the basis that a reaction between two or more chemicals requires (at the molecular level) a collision between two rapidly moving molecules. If the two molecules collide in the right way and with enough kinetic energy, one of the molecules may acquire enough energy to initiate the bond-breaking process. As this occurs, new bonds may begin to form, and ultimately reagent molecules are converted into product molecules. The point of highest energy during bond breaking and bond formation is called the transition state of the molecular process. The difference between the energy of ...

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