Changes Around Us-Physical And Chemical change, Characteristics
§§ Physical and chemical changes:
All substances around us undergo changes. In some cases, the changes are small and difficult to defect. In other cases, the changes are obvious and easy to defect. These changes generally get accerelated if we heat the substances.
Most of these changes can be classified under two headings.
a) Physical change b) Chemical Change
Physical Change
A physical change is one where there are changes only in the physical properties of the components. For example, when a pure gold ingot is melted, then it changes from solid gold to liquid gold. However, there is no change in the chemical composition of the component, which is gold, in case of physical changes.
In the example of the gold ingot, the observed changes are listed below:
1. The solid gold ingot changes to liquid form. Cooling it back will help the gold retain its solid form again, though there be changes in its shape.
2. The temperature of the liquid gold is quite high, and it can be reversed back to its original temperature by cooling it.
3. The shape of the solid ingot changes when it is liquified. Using proper methods of shaping and casting while cooling the liquid gold can help get back the original shape.
These are all changes in the physical properties of the material and no chemical change takes place.
Definition of Physical Change: A physical change is one that changes the shape ,size,physical state,and appearance of a substance, but not its chemical composition.
How to Identify a Physical Change?
Sometimes, identifying and classifying a change as a physical change might seem difficult and seemingly impossible. The following pointers can help you understand whether a change is physical or chemical in nature.
In most cases, a physical change is reversible in nature. However, changes which involve breaking and physical deformation might be irreversible under normal circumstances. They can also be turned back to their original form using sophisticated recycling and reformation techniques.
If there is a color change or evolution of gas bubbles, the change might no longer be physical in nature.
If the product formed has completely different properties as compared to its constituents, it is no longer a physical change. In physical changes, the chemical composition of the constituents remains the same and the product would be able to exhibit the properties of the parent constituents.