What happens to the particles when a physical or chemical change occurs?
it is when particles react to the substance in which it has been placed with
What is always a characteristic of a chemical change but not always a characteristic of a physical change?
When a chemical change takes place, the chemical structure of particles involved changes (i.e. one or more new substances are formed). In a physical change, the physical state of the particles involved changes (e.g. a solid melts and becomes a liquid). The chemical structure of the particles does not change, and no new substance is formed.