What causes a State Change

Have you ever wondered why when the temperature is -10 degrees Celcius, you may still find liquid water?  Or why does a bot of boiling water not completely evaporate when its temperature reaches 100 degrees Celcius?  The answer to these problems and many more is that temperature is not the only factor that contributes to chemical change.  

Before exploring the cause of state changes, we must first examine what the state changes are.  When a substance goes from a solid to a liquid, the process is called fusion or melting.  When a liquid reverts back to a solid, it is called solidification or freezing.  When a liquid transforms into a gas, it undergoes the process of vapourization or evaporation.  On the rare occasion that a solid skips the liquid stage and shifts into a gas or vice-versa is called sublimation.   

The overarching factor in the world of state changes is the kinetic energy of the molecules of the substance.  A solid has very slow moving molecules that are tightly bound together, which means that there is a very low kinetic energy.  By increasing the temperature as well as the kinetic energy of the molecules, one can instigate fusion.  This is because the molecules in liquid water are much more free-moving, with a great deal more kinetic energy.  

However, the kinetic energy of a liquid is still much less than the molecules that make up a gas.  Gas particles are free to move with little to no restriction, resulting in extremely high particle velocities and kinetic energy values.  Thus, one must add a great deal of energy from an outside heat source in order to instigate the process of vapourization.  

If a great deal of energy is added to a solid within a very short timeframe, sublimation make take place.  However, this is very unlikely to occur, because enough energy must be absorbed to raise the temperature of the solid past it’s boiling point, as well as enough energy to speed up the molecules so as to move them into the next state of matter.   

Everything in our physical universe has the potential to alter its physical state.  However, vast amounts of energy are needed to do this, more than to simply alter the temperature of the substance to a certain point.  Thus, many natural conditions don’t provide enough energy to change a substance’s state, we observe phenomena such as freezing-cold or boiling-hot liquid water.