Difference Between Chemical and Physical Change

CHEMICAL VS. PHYSICAL CHANGE

Have you ever wondered what the difference is between chopped wood and burnt wood? Or why rust is different from plain iron? These are examples of physical and chemical changes. These two distinctions are better understood if we study how matter is merely cosmetically altered and reacts to chemical interaction. The best and simplest way to differentiate the physical and chemical change is by remembering that physical change only affects how we perceive the material while chemical change actually alters the material down to its molecular composition.

Physical change is very common. You can see it in the aforementioned chopping of wood. A tree is chopped down. Then, it runs through a saw mill. The end result is you have lumber. But did the wood itself change? It’s still the same composition, down to the sawdust on the floor. Another good example is water. Put it in a glass and it is still water, but has the shape of the glass. Place it in the freezer and you have ice. It’s solid now, but did the composition change? Or how about boiling it at such a high temperature that it turns to steam? It’s still H20 but in gaseous state. No change occurs that alters the molecular structure of the substance during physical change. In simple terms, physical change may alter how we perceive the material but, at its most basic level, it still maintains the same composition.

Chemical change is an entirely different question. This is like a person whose memories are transferred to a completely new body and personality. The memories and past experiences are still there but this is an entirely different person altogether. One of the simplest examples of chemical change is when iron rusts. Leave a piece of iron unattended and, given time, it will have brownish blemishes, forming rust. Leave it out for even longer and, eventually, the entire iron piece is now rust or iron oxide. At the molecular level, the iron molecules interacted with the oxygen in the atmosphere to form an entirely new substance whose properties are very little like the two elements that combined to form it.

There are instances when both physical and chemical changes occur. One of the simplest forms of this is when you burn sugar. Physically, it turns into a black husk of its former self (leaving the carbon residue i.e. ash). On the molecular level, it also changes. The basic chemical formula of sugar is C6H12O6 (the formula for glucose). Other chemical changes are the release of CO2 (carbon dioxide) and H2O (water), the latter in the form of water vapor, from the composition of the original form. If, say, you burn sugar with the purpose of cooking, there are a wide array of physical and chemical changes that could occur.

There are a few basic rules to understand when a chemical change occurs. First, there has a certain amount of energy expended in the process. Whether it is in the form of electricity, light or temperature changes, a minimum amount is used for chemical changes to occur. The reason for this is because the very bonds that forms the substance would have to be altered for the change to take effect, and these three forms of energy are the catalysts. Second, the molecular bonds mentioned before would have to react, often dispersing or colliding with the other molecules or atoms involved in the process. Third, different materials have different reaction times. One material may change faster than another in the same conditions; also known as rate of chemical reaction.

The biggest distinction with physical change and chemical change is the fact that the former is superficial; if certain conditions are met, it is reversible. For example, a torn shirt can be sewn back to good as new. A chemical change, is irreversible; if you burn that shirt to a cinder, no amount of sewing will make it new again.

Summary:

1. Physical Change means the material is only physically altered but does not change its molecular structure; Chemical change alters the basic molecular structure of the material.

2. A Chemical change may also cause a physical change; a physical change alone cannot lead to a chemical change.

3. A Physical change is superficial and can possibly be reversed; a chemical change is complete and permanent.

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