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Boiling Water Chemical or Physical Change

To answer whether boiling water is a chemical change or a physical change one has to first define what is boiling and what is the change brought about in the physical or chemical state by boiling. Taking the three parts one by one let us first define boiling.

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Is Boiling Water a Physical or Chemical Change?

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While boiling, only physical change is occur in the case of water. Boiling a liquid involves the process of heating it continuously for some length of time until its vapor pressure becomes equal to the pressure of surrounding environment and a continuous process of conversion of liquid to vapors (gaseous form of the liquid) commences. At this point the temperature of the liquid becomes constant and further continued heating does not result in any further rise in temperature of the liquid. Following picture shows the rise and ultimate stabilization of temperature at boiling point for one such experiment.


Boiling Water Graph
This happens because the heat energy gets absorbed by the molecules to acquire further kinetic energy, called latent heat of evaporation to break through the liquid and rise as vapor. At this stage one can see bubbles forming at the base of the beaker or pan in which water is being boiled and rising of these bubbles to the surface and breaking through to rise as vapor.

During the process of boiling if the water vapors are collected and cooled then the water is obtained again. Thus the forming of vapors is seen to be a reversible process. Water obtained by condensation of vapors as also the boiling water left in the pan show the same chemical properties as the water that was taken for experiment. This shows that boiling water results in no chemical change. If water is just heated to its boiling temperature then there is a physical change of rise in temperature and if it is boiled for some time then there is a physical change from liquid to gaseous state.


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