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Effect of particle size on rate of chemical reaction

Investigatory project on study of the effect of particle size on rate of chemical reaction


In reactions involving solids, the reaction usually takes place on the surface and the rate of the reaction depends on the surface area of the solid particles. The greater the surface area, the higher will be the rate of the reaction. The surface area of a given mass of solid depends on the size of the particle. For a given amount of a solid, the surface area increases with the decrease in size of the particle. So smaller the particles, greater will be the rate of reaction.


The objective of this project is to study the influence of the size of particles on the rate of a reaction by considering the reaction between marble and hydrochloric acid.

CaCO3 + 2HCl ---> CaCl2 + H2O + CO2


250 mL beakers, Marble pieces, HCI acid, Stop watch


Take one single piece of marble weighing 2g. Similarly take 2g samples of coarsely powdered marble and finely powdered marble. Place the three samples in three different beakers. Add the same quantity of 2M HCl (not less than 50 mL) to each of them. There should be enough acid to completely immerse the samples. As soon as HCI is added, start a stop watch. The contents may be shaken at regular intervals. Note the time taken in each case to complete the reaction. The reaction will be slowest when a single piece of marble is reacted. It is fastest when finely powdered sample is reacted.


Nature of marble (2g)

Volume of 2M HCl in mL

Time taken to complete the reaction




Fine powder

Coarse powder

Single piece








It is observed from the experiment that minimum time is taken for the completion of reaction when marble is in the powdered form.


The rate of reaction of a solid substance is proportional to the surface area of the sample.


1. How does the rate of a reaction vary with increase in surface area?

Ans: Rate of a reaction increases with increase in surface area

2. Why are powdered substances more reactive than substances in lump states?

Ans: Surface area of powdered substances are more than that of a substance in the lump state.

3. What is the action of dil.HCI on marble?

Ans: Marble reacts with HCl to liberate CO2.

4. Write the reaction between marble and HCl

Ans: CaCO3 + 2HCl ---> CaCl2 + H2O + CO2

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