CBSE XII - Chemistry Projects
( Study the Rate of Evaporation of Different
When a liquid is placed in an open vessel, it slowly escapes
into gas phase, eventually leaving the vessel empty. This phenomenon is known as
evaporation. Evaporation of liquids can be explained in terms of kinetic
molecular model. Although there are strong inter-molecular attractive forces
which hold molecules of a liquid together, the molecules having sufficient
kinetic energy can escape into gas phase if such molecules happen to come near
the surface. In a sample of liquid all the molecules do not have same kinetic
energy. There is a small fraction of molecules which have enough kinetic energy
to overcome the attractive forces and escape into gas phase.
Evaporation causes cooling. This is due to the reason that
the molecules, which undergo evaporation, are high-energy molecules; therefore
the kinetic energy of molecules which are left behind is less. Since the
remaining molecules have lower average kinetic energy therefore, temperature
must be lower. If the temperature is kept constant the remaining liquid will
have the same distribution of molecular kinetic energies and the high-energy
molecule will keep on escaping from the liquid into the gas phase. If the liquid
is taken in an open vessel, evaporation will continue until whole of the liquid
Clean and dry the petridishes and mark them as A, B, C.
Pipette out 10 ml of acetone to petridish A and cover it.
Pipette out 10 ml of benzene in petridish B and cover it.
Pipette out 10 ml of chloroform in petridish C and cover
Uncover all the three petridishes simultaneously and
start the stop-watch.
Note the respective time when the liquids evaporate
completely from each petridish.
Time taken for complete evaporation
The rate of evaporation of the given three liquids is in the order:
Chloroform > Benzene > Acetone