What does it mean when there is a physical change?
3?

A physical change is a change to the physical—as opposed to chemical—properties of a substance. They are usually reversible. The physical properties of a substance include such characteristics as shape (volume and size), color, texture, flexibility, density, and mass.

space exploration has led to the development and technological improvement of many everyday items. (if this answer is wrong i will find the right answer) : )

o conteúdo de calor de um sistema é igual à entalpia apenas para um sistema que é constante