Why compounds are always homogeneous but mixtures can be either homogeneous or heterogeneous?

Answer 1

Solids are always homogeneous because the molecules or atoms that make up the solid are evenly dispersed throughout the solid. Frozen water, for example, is a homogeneous solid because the water molecules are frozen in a crystal like structure called a lattice, which causes the water molecules to be uniform throughout the solid. However, if you were to melt the frozen water into liquid water, and add table sugar without completely dissolving the sugar, you wouldn't have a homogeneous mixturebut rather a heterogeneous mixture. This is because some sugar would be on the bottom of the mixture. Therefore, the concentration of sugar would be greatest on the bottom of the mixture, and lowest in the top of the mixture. Because the sugar is not present uniformly throughout the water, you have a heterogeneous mixture. However, if you were to dissolve all the sugar, you would uniformly spread the sugar out over all the water, and create a homogeneous mixture.

Answer 2

This condition basically follows from the definition of homogeneity as constancy of composition within even a very small sample. By ordinary analytical techniques, composition can only be measured in a sample sufficiently large to contain a very large number of individual molecules or formula units. Because each individual molecule or formula unit of a compound contains atoms in the same proportions, the same must also be true for any number of such molecules or formula units.

Somewhat paradoxically, compounds are not literally homogeneous by the classical definition given above when measured by techniques capable of detecting individual atoms. However, the classical definition based on analytical techniques available before about 1930 has been generally retained for convenience.

Answer 3

because compounds have to do with a chemical change...

Answer 4

Compounds are homogeneous, mixtures are heterogeneous.