A material can undergo either a chemical change, physical change, or sometimes both.
The key differences between chemical and physical change are seen in terms of visible variation in forms.
In a physical change, there is always an alteration that can be perceived by our five senses. Like in terms of appearance, smell, temperature, etc.
While in a chemical change there is variation in the chemical composition of the material.
The Physical change can be seen by a modification in color, states of matter (transition from solid liquid or gas), or texture, etc.
An example of physical change is the conversion of ice into water.
Here you can notice the physical alteration occurs in terms of a difference in colors i.e. white to colorless, as well as transition in the state of matter i.e. solid to liquid.
Whereas a chemical change is one where there is a significant alteration in the chemistry of the material.
However, in some cases, there can be variations in the physical features too.
The chemical change mostly involves the formation of a new substance. I.e. there is a modulation in the chemical nature of the molecules or atoms within the matter.
Chemical alteration of the molecules can modify the appearance in terms of color or texture and sometimes even in the states of matter.
Differences Between Chemical and Physical Change
| Sl. No | Feature | Physical change | Chemical change |
|---|---|---|---|
| 1 | Appearance | Always there is a physical change in terms of appearance or touch or smell etc.. | There is a change in chemical composition, but physical aspects may also change due to it. |
| 2 | Chemistry | The chemistry is Intact. | The chemistry is modified. |
| 3 | Occurs when | Exposed to Physical force, pressure or a differences in the temperature. | Exposed to high temperatures or mixing with other substances. |
| 4 | Occurs due to | Due to an change in termperature, application of physical force, excess moisture etc. | Due to changes in temperature, exposure to air, sunlight, moisture, etc. A chemical change occurs due to an interaction between two or more substances. |
| 5 | Extent of variation | There could be alteration in intermolecular forces of attractions or energy states of bonds. | The chemical process involves the rearrangement of atoms Or changes in molecular structure. |
| 6 | Rate of transition | Comparatively, physical modification in most cases is slower and proceeds over a period of time. | Chemical modification is rapid, like in fraction seconds in most cases, and occurs instantly. |
| 7 | Control or Regulation | The transition can be stopped midway from further progress. | The modification is hard to be stopped from further progress. |
| 8 | Reversal | Physical transformation in some cases can be completely reversed. | Chemical transformation is mostly irreversible. |
| 9 | Occurrence | Physical variation rarely occurs in nature or does not occur regularly. Example; conversion of water into water vapor | Chemical variation is a common phenomenon in nature. It occurs regularly by Chemical reactions like neutralization, complexation, oxidation, etc. |
| 10 | Examples | Conversion of wax into liquid, naphthalene into volatile gas, formation of precipitate. | Degradation of drugs, chemicals over time, oxidation of oils. |
Examples for better understanding
For a chemical change, you can notice the change occurs physically but is related to chemical modification.
1. An example of chemical change is the formation of foam or effervescence when lemon juice is mixed with sodium bicarbonate (baking soda).
Here what actually happens is when you add lemon juice into a powder of sodium bicarbonate, immediately there is a chemical modulation leading to the formation of carbon dioxide and sodium citrate salt.
2. Transition in the color of potassium permanganate when reacted with oxalic acid.
3. The foul smell of oils due to oxidation of fatty acids in them when exposed to air for a long time.
Examples for physical changes include
When heated, the solid form of ghee melts to liquid form and, when cooled, again converts to solid.
- Metals like iron, when heated, expand with red coloration due to excess temperature. But, again condense on cooling down.
Examples for both physical and chemical change
- Precipitate formation of Silver chloride when silver nitrate reacts with Chloride ions in water.