Introduction :
The matter is able of witnessing changes, which are classified as either physical or chemical. Physical changes in matter are reversible An ice cell can melt into liquid water, and also the liquid water can be firmed back into an ice cell. Chemical changes, on the other hand, aren't reversible A log burned in a fire turns to ashes, but the ashes can not be changed back into a log.
Physical change :
Here only the phase or appearance of the substance is changed. The chemical composition of the substance remains unchanged. This change is reversible.
Chemical change :
Here the chemical composition of the substance is completely changed. ie) The substance is changed into an entirely different substance with a new chemical formula. It is irreversible
General difference between Physical and Chemical change
| Physical Change | Chemical Change |
| When a substance undergoes a physical change, its composition remains the same despite its molecules being rearranged. | When a substance undergoes a chemical change, its molecular composition is changed entirely. Thus, chemical changes involve the formation of new substances. |
| Physical change is a temporary change. | A chemical change is a permanent change. |
| A Physical change affects only physical properties i.e. shape, size, etc. | Chemical change both physical and chemical properties of the substance including its composition |
| A physical change involves very little to no absorption of energy. | During a chemical reaction, absorption and evolution of energy take place. |
| Some examples of physical change are freezing of water, melting of wax, boiling of water, etc. | A few examples of chemical change are digestion of food, burning of coal, rusting, etc. |
| Generally, physical changes do not involve the production of energy. | Chemical changes usually involve the production of energy (which can be in the form of heat, light, sound, etc.) |
| In a physical change, no new substance is formed. | A chemical change is always accompanied by one or more new substance(s). |
| Physical change is easily reversible i.e original substance can be recovered. | Chemical changes are irreversible i.e. original substance cannot be recovered. |
It's all about the theoretical part. Now we are going to explore this concept by seeing the well known chemical reactions. Here we are going to see four different sets of reactions
Consider the Iron (Fe) is oxidized to Iron oxide ( Fe2O3 )
4 Fe + 3 O2 → 2 Fe2O3
Here, Fe is completely changed into Fe2O3 (a different substance). Hence it is a Chemical change
Consider the Copper (Cu) react with Hydrochloric acid (HCl)
Cu + HCl → No reaction
Cu is a less reactive metal. The reduction potential of Cu is higher than Hydrogen. Therefore Cu can't replace the Hydrogen in HCl to form CuCl2. The metals which have reduction potential lower than Hydrogen can react with HCl. Hence Cu doesn't react with HCl
Here there is no reaction. Hence there is neither physical change nor Chemical change
Consider the Ice melt to water
Ice (Solid H2O) → Water (Liquid H2O)
Here there is the only phase of the substance is changed. There is no change in chemical composition ie) both are having the same chemical formula H2O
Hence it is a Physical Change
Consider Sodium (Na) reacting with water
2 Na + 2 H2O → 2 NaOH + H2
Here Sodium (Na) is completely changed into a new substance Sodium hydroxide (NaOH)
Hence it is a Chemical change
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