A change in form or state, such as melting or dissolving, that does not alter chemical identity.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
A physical change alters the form, state or arrangement of matter, but the molecules or formula units themselves remain the same. Changes of state, such as melting, boiling and freezing, are physical because only the spacing and energy of the particles change. Dissolving a solid in a solvent, or bending a metal, are also physical changes. The energy involved is usually the intermolecular or lattice energy, not the energy of covalent bonds inside molecules. Physical changes are generally easy to reverse by restoring the original temperature or pressure.
Key ideas: A physical change alters form or state but not the chemical identity: melting, boiling, dissolving, crushing, freezing, sublimation. It is usually easily reversible, and no new substance forms, so the molecular formula is unchanged. Energy is still involved, for example water needs about 334 J per g to melt and 2260 J per g to vaporize.
Common mistakes and connections: Students think dissolving sugar or salt is a chemical change because the solid seems to vanish, but the particles are still there and can be recovered by evaporation. Not every physical change is easily reversible either, such as shattering glass. Contrast with chemical change and connect to phase diagrams and enthalpy of fusion.
Melting, boiling and freezing of water are physical changes: the state changes with temperature and pressure but the H2O molecules stay the same. The interactive lesson shows this as a live animation or chart.
Ice melting to liquid water is still H2O, so cooling the water back to ice reverses the change completely.
A change in form or state, such as melting or dissolving, that does not alter chemical identity.
Physical Change is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Compound, Mixture, Pure Substance.
The next topics in Atomic Structure & Periodicity are Chemical Change and Law of Conservation of Mass.
Yes. The interactive lesson includes a self-check question on Physical Change, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Physical Change is topic 7 of 115 in Atomic Structure & Periodicity.