I am investigating the rate of reaction between hydrochloric acid and sodium thiosulphate. The variable I am going to change will be the temperature; I will raise the temperature by approximately 10oc each time.

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Clare Apps         Year 11 assessed practical

I am investigating the rate of reaction between hydrochloric acid and sodium thiosulphate. The variable I am going to change will be the temperature; I will raise the temperature by approximately 10oc each time.

Other possible variables that could be changed are; changing the concentration of the acid, increasing the pressure by reducing the volume  of the container which means the particles will be closer together which would result in faster collisions. Using a catalyst would speed up a reaction and changing the surface area could speed up or slow down the reaction.

When the two chemicals are added together, they start to react. It will give off sulphur as one of the products. This is called a precipitation reaction.

The equation between sodium thiosulphate and hydrochloric acid is:

Na2 S2 O3(aq) + 2HCl(aq)                                     2NaCl(aq) + S(s) + SO2(g)

A chemical reaction can only occur between particles when they collide. The faster the particles are moving, the more energy they have. Fast moving particles are more likely to react when they collide. Particles will move more quickly when the temperature is raised. The same amount of sulphur will always be produced, but at different rates.

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There is a certain amount of minimum energy needed in order for colliding particles to react with each other. If the colliding particles have less than this minimum energy, (because they aren’t moving fast enough), then they just bounce off each other and no reaction occurs, this is called elastic energy. The minimum energy is called the activation energy.  

The temperature will speed up the rate of reaction because the hotter the particles are, the more energy they have which means they will move faster and are therefore more likely to collide into each other.

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