Physical vs Chemical Change
There are many who would be tempted to say that a change is a change and why bother to make a distinction of physical and chemical change. But it is important to understand the differences between these two types of changes as they affect our lives and environment also.
You must have observed changes in daily life too. Your fridge converts water into ice and your humidifier converts water into steam. Both are physical changes as they are merely changing the form of matter and the reactions can be reversed. Ice readily changes into water while steam also converts into water upon cooling. When you crush a can, you are merely causing a physical change in the shape and size of the can. Similarly, when you add salt or sugar to water to make solutions, it is a physical change as you can easily separate salt and sugar from the solutions to get original substances.
A chemical change is a reaction in which matter gets converted into another type of matter. The reaction is irreversible and you cannot get back the earlier material. When the body of your car rusts, it is a chemical change as iron has oxidized to produce rust. Similarly when you burn wood, you get ash and charcoal which have different properties from wood and you cannot reverse the process to get back wood. On the other hand no matter how many small pieces of a paper you cut, it still remains paper and there are no changes in its properties. But if you burn paper, what you get is carbon and not paper. So a change, if it results in altogether different substances is a chemical change whereas if the properties of the substance remain the same (as in water becoming ice), it is called a physical change.
When you are eating, the food is in one form but the process of digestion takes place which converts food into proteins and carbohydrates to fulfill the requirements of your body. The process of digestion is thus termed a chemical change.
• A physical change merely changes the shape and size of the substance while a chemical change produces altogether new substance
• Physical change is reversible while chemical change is irreversible
• In general, physical changes are fast whereas chemical changes are slow
• In a physical change only the state of matter changes while it still has the same properties. On the other hand, in a chemical change (it takes place at a molecular level) and the new substance formed has altogether different properties.