Basic Chemistry | Changes

Chemistry : Why does water turn into vapour on heating? 

“Changes” it is very important topic of chemistry. Usually, In day to day life, we tend to consider ‘all types of changes are same’. But, In science, there are two types of changes which are different from each other. Let’s explore why does water turn into vapour on heating?

Before differentiating between types of changes, let’s define what changes are. 
• Changes : When one object get some activity, and there is some sort of movement, and becomes different from the initial substances, then we can say that some ‘change’ take place. 
I think it is not difficult to understand what is the exact meaning of change. So, let’s start the types of changes. 
• There are two types of changes - 
   1. Physical Change   2. Chemical Change

Physical Change : When the change take place in substance, in such a way that the force of attraction between it’s free entities (molecules) changed. 
- To understanding it very properly, we use take the example of water. 
We know that the chemical formula of water is H2O . So, we can say that the molecular formula of water is H2O. (Whenever we talk of chemical formula of any substance, we will taking of it’s molecular formula). So, before understanding it more properly let's understand one more concept of physics. That is : to change the force of attraction or force of gravitation between two masses, we’ve to apply some external energy in it. 
So, Let’s back to water. 
Chemical formula of water is H2O in any of it’s physical state. Either it is in liquid form, or in solid (ice) form or in gaseous (vapour) form, it’s chemical formula will H2O. We also know that one glass of water contains millions and millions of water molecules. In other words, one molecule of water is very small and can’t be seen with naked eyes. We require a microscope for it. So, whenever heat is putted water that heat energy give rise into kinetic energy. Due to that kinetic energy, molecules of water start moving. When temperature is increased, more kinetic energy increased. And thus movement of molecules get fast. And thus force between two molecules get reduced and then there becomes a gaping between two molecules. If there is gap between two molecules, same amount of water will occupy larger volume that of earlier. Consider that in initial state, it was in liquid form. Then when it starts occupying more volume, it is converted into gaseous form. We can say that heat is that agent which makes the reduction of force between the molecules of water. (It’s concept, not the definition of heat) . 
So, that is why, when heat is putted in water or when water is heated, water get converted into vapour. Same condition will happen when it becomes gas to liquid. Why? It’s heat energy is reducing thus it's kinetic energy is also reducing and then the movement between two molecules also reduced and the force of gravitation increased this it becomes liquid. 
I hope that the concept is now crystal clear.


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