* Chemical Reaction: Involves the breaking and forming of new chemical bonds, resulting in the formation of new substances with different properties.
* Physical Change: Changes the form or appearance of a substance but doesn't alter its chemical composition.
What happens when sodium chloride melts:
* The heat energy causes the ions in the solid NaCl crystal lattice to vibrate more rapidly.
* The vibrations become so strong that the ionic bonds holding the lattice together weaken and break.
* The ions are now free to move past each other, resulting in a liquid state.
Key Points:
* The chemical formula of sodium chloride (NaCl) remains the same throughout the melting process.
* The change is reversible - you can solidify the melted NaCl by cooling it down.
Therefore, the melting of sodium chloride is a physical change because it only alters the physical state of the substance, not its chemical composition.
