How do we differentiate chemical change from physical change

In a physical change the nature of the substance, the particles of which it is composed and the numbers of particles remain unchanged. In a chemical change the properties of the new substances are different from the original, the particles are different and the number of particles can change.

Chemical change :has change in mass, heat is needed, new element is formed, hard to reverse

Physicalchange:does not have change in mass, heat is not necessary, no new element is formed, easy to reverse

not clear

why is arctic sea ice important? arctic sea ice keeps the polar regions cool and moderate global climate. sea ice has a bright surface; 80 percent of the sunlight that strikes it is reflected back into space. as sea ice melts in the summer, it exposes the dark ocean surface.