Aim: To study and investigate the effect of temperature on the rate of the reaction between sodium thiosulphate and hydrochloric acid.

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VIKRAM GANESHAN

11-D

CHEMISTRY HL

Planning (a)

Aim:

To study and investigate the effect of temperature on the rate of the reaction between sodium thiosulphate and hydrochloric acid.

Theory:

For a reaction to take place the particles of the reactants have to collide. As particles approach each other there is repulsion between the electron clouds of the particles. In order for the reaction to occur the collision must have sufficient energy to overcome this repulsion. Frequently energy is also required to break some of the bonds in the particles before the reaction can take place. The collisions that result in a chemical reaction are known as effective collisions. In order for effective collisions to take place, a minimum amount of energy called activation energy is required which varies from reaction to reaction. Thus in order for a reaction to occur, the particles must collide and the collision must be energetically effective so as to overcome the activation energy of the reaction. The steric factor must also be taken into consideration as the collision must bring the reactive parts of the molecule into contact in the correct orientation. Thus if anything increases the collision rate, the reaction rate also increases.

The rate of a chemical reaction depends on a number of factors.

  1. Size of particles
  2. Concentration
  3. Temperature
  4. Addition of a catalyst
  5. Pressure of a gaseous reactant

During the experiment, as we increase the temperature the average kinetic energy of the particles increase, resulting in a larger number of particles having activation energy. This in turn results in more effective collisions, increasing the speed of reaction.

The reaction between sodium thiosulphate and hydrochloric acid proceeds to the following chemical equation:

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + SO2(aq) + H2O(l) + S(s)

This equation can also be represented in the ionic-equation form in the following manner:

S2O32- + 2H+ → H2O + SO2 + S

The sulphur dioxide thus formed is dissolved in water as sulphurous acid. The partially dissolved sulphur makes the solution turbid due to the formation of a colloid. Because of this, the solution turns more dirty and opaque as the liberated sulphur increases in quantity. This property is used in the experiment to determine the rate of the reaction.

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Hypothesis

It can be hypothesized that as the temperature is increased the reaction rate too will increase. Firstly with an increase in temperature, the probability of more number of particles having greater energy than the activation energy also increases. Secondly the more frequent collisions having higher energy, the probability of effective collisions also increase thus increasing the reaction rate. But it must be noted that the graph of reaction rate against temperature will not be a linear graph alike the one drawn against concentration because although temperature is proportional to the reaction rate, it varies as a square function ...

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