Physical change means that although the state of matter has changed, generally speaking, the composition of matter itself has not changed. For example, changes in position, volume, shape, temperature and pressure, as well as mutual transformation between gas, liquid and solid, etc. The interaction between matter and electromagnetic field, the interaction between light and matter, and the interaction and transformation between microscopic particles (electrons, atomic nuclei, basic particles, etc.) are all physical changes.
Concept: A change that does not produce new substances (Physical changes are only changes in the shape and state of substances)
Substance: retention substance chemical property The smallest particle itself remains unchanged, but the interval movement between particles has changed, and no new matter has been generated. Many students will confuse physical changes with chemical changes. In fact, the fundamental difference between physical changes and chemical changes is that physical changes do not generate new substances, while chemical changes do (for example, the process of copper forming verdigris is chemical changes)
Macro: no new substance is generated
Microscopy: the distance between the atoms constituting the molecule remains the same (the chemical bond length remains the same), the shape and size of the substance changes, the molecule itself remains the same, and the combination mode of the atoms remains the same.
The basic three state change of matter is a physical change because no new matter is produced. Deliquescence of NaOH and other inorganic salts and alkalis, melting of ice, grinding of alum, etc.
For example, if molten iron is cast into an iron pot, which involves the combination of carbon and iron with new molecules (generally Fe3C), it is not considered as a physical change, but if it is 100% pure iron, no chemical change will occur when cast into an iron pot, and no new phase will be generated. [1]
After looking up and browsing the relevant information, we also know that under certain conditions, graphite turns into diamond Chemical change Because it has become another simple substance. But there are also some Allotrope The transformation of is a physical change, such as Monoclinic sulfur and Rhombic sulfur 。 Before and after the physical change, the type, composition and chemical properties of substances remain unchanged. The essence of such changes is that the aggregation state of molecules (separation distance, movement speed, etc.) has changed, leading to the change of the shape or state of substances. Physical changes represent the physical property 。 Physical changes are essentially different from chemical changes. Flame reaction It is a physical change. The flame reaction is the change of the electronic energy level in the atom of the substance, which is generally the change of the electronic energy in the atom, and does not involve the change of the structure and chemical properties of the substance. Petrolic fractionation Tire explosion Physical property: color, state ， smell , hardness, magnetism, density, melting point, boiling point, solubility, freezing point ， Thermal conductivity ， Conductivity , extensibility, volatility ， Water absorption , whether it is soluble in water, etc. 
