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Rates of reaction

GCSE: Chemistry

Title:  Rates of reaction
Description  Sodium thiosulphate and hydrochloric acid. Varying the heat. 2006 A grade.
Word Count:  2000

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What is Rate of Reaction?
The Rate of a reaction tells us how quickly a chemical reaction happens. Fast reactions, like dynamite exploding start and finish within a fraction of a second. Slow reactions like concrete setting, may take days, weeks or even years to finish. During a reaction we can measure how much reactant is used up in a certain time.


In this coursework I plan to investigate the effect of varying the temperature of sodium thiosulphate on the rate of reaction between dilute sodium thiosulphate Solution (ST), Hydrochloric Acid (HCL). The symbol equation for this reaction is:
2HCl(aq)+Na2S2O3(aq) 2NaCl(aq)+SO2(g)+S(s) + H2O(l)


There are many factors that can affect the rate of a reaction. These factors consist of the concentration of particles, the temperature of the reactants and the surface area. In my experiment I will vary the temperatures of the reactants and keep all other factors constant to the best of my ability. Changes in temperature can affect the rate of reaction because the more heat that is applied the particles will have greater energy and cause more collisions. When a collision happens the two particles that have collided cause a reaction to occur. However these particles must have enough energy to break down existing bonds the particles have. This is why I have predicted the rate of a reaction is when
‘The higher the temperature of sodium Thiosulphate the faster the reaction’.

Background Information / Scientific Theory

The rate of reaction should increase when the temperature increases or a chemical substance is added that is very reactive. This is due to a theory called the collision theory. A reaction can only occur when the particles collide with enough energy to break existing bonds. A chemical change can only take place with a fixed amount of collisions by the particles. These are often referred to as successful collisions. The successful collisions have a sufficient amount of energy at the moment of impact, causing existing bonds to break to form new bonds. By rising the temperature or chemical substance is added that is very reactive, more collisions would happen and therefore more successful collisions, which will increase the rate of reaction. According to the Collision Theory, the average kinetic energy of the reactant molecules should increases, and this should increase the impact energy upon collision.

The following diagrams show what happens to the particles when sodium Thiosulphate is added to hydrochloric acid.

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