What is the difference between a pure substance and a mixture? how are the atoms different?

Pure substances cannot be separated into any other kinds of matter while a mixture is a combination of two or more pure substances

A pure substance has constant physical and chemical properties while mixtures have varying physical and chemical properties

The atoms are different by prime difference lies in the fact that pure substances cannot by physically separated while mixtures can be (physical methods)

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

catya your not at all which answer i've seen you do this on another question!