What is the difference between a chemical reaction and a physical reaction?

Answer 1

A physical reaction, such as boiling water or dissolving salt in water results in no change in the chemical makeup of the original species. Salt can be recovered by evaporation of water. Water vapor can condense to water. A chemical change, such as burning wood or tarnishing of silver, is a chemical change. The chemical constituents of the wood and silver are changed. I.E., burning wood that contains hydrocarbons, results in the formation of CO2. Silver, left out in the open, is oxidized by oxygen to form silver oxide.

Answer 2

A chemical change is one where the identity of the substance changes. An example could be burning paper (paper and oxygen are converted into ash, carbon dioxide, and water) or iron rusting (iron and oxygen are converted into iron oxide).

A physical change is one where the substance retains its identity but its physical state changes in some way. The classic example is water boiling or ice melting. These processes are changing the state of the substance H₂O (liquid to vapor, solid to liquid) but the identity of the substance is unchanged. Snapping a popsicle stick into two pieces is also a physical change, as is cracking an egg.

Many chemical changes are reversible, so I would caution you against thinking about chemical changes as being processes that are irreversible or that cause a substance to be unrecoverable as a result of the change. Similarly, physical changes may not always be reversible (like cracking an egg). Hope this helps!

Answer 3

In a chemical reaction, it is impossible to get the original species back. Example: curdling of milk is a chemical reaction, no way for us to restore the milk.

Physical change it is possible to get the original substance back by some simple physical method like evaporation, boiling.