what is the differance in chemical reactivity in L-ascrorbic vs ascrorbic acid?

Answer 1

ascorbic acid has two optical isomers: L-ascorbic and D-ascorbic acid

In general, there is no difference in the chemical reactivity of the two forms. However if you are using reagents that are stereo-selective, like enzymes, then only one form will be used in the reaction. Usually that would be L-ascorbic acid.
If you have the racemic mixture of the two forms, then you would have 50% of the mixture being L- and 50% D-, so you would have half the concentration/amount of what you would like reacting (for stereoselective reactions with enzymes in vitro or if you are doing experiments with living organisms).

Answer 2

L-ascorbic acid can rotate polarized light to the left. It is an optically active molecule.