If there is 8 g of a substance before a physical change, how much will there be afterwards?

There will be 8 g.

Explanation:

Physical changes keeps intact the molecular structure of substances.

A typical example of physical change is changing the state of matter of a substance: although its density, temperature or shape may vary, the mass will remain the same.

Back in the 18th century, Antoine Lavoisier, noticed that, in physical process, non mass nor energy went missing before and after.

"Nothing is lost, nothing is created, everything is transformed"