Since you posted in the Mulch Forum, I assume you are using these woodchips for garden paths, in garden beds, as a top dressing or in
compost, or all of the above.
Hardwood chips are from deciduous
trees like the ones that lose their leaves in the fall. Softwood comes from a conifer like pine, cedar, and cypress.
The hardwood chips will last longer before breaking down.
You can scratch softwood easier than you can scratch hardwood.
You may also be able to tell by the smell of the
wood. That is why different woods are used in BBQ to give the food different smells.
I hope other members can offer you some better suggestions.