Orders of reactions

Hi,

Why is it that a second or first order reaction can't go to completion and are there any modifications that can be done to an experiment where they will.

Also how do you work out the rate equation from a graph?

Any advice would be helpful.
Thanks in advance

The graph of rate vs concentration of a second order reaction never touches conc.=0 point
Except for zero order reactions..no other order reaction goes to full completion.

Rate/Conc graph: Horizontal line is zero order, straight line going through origin is 1st order, exponential is 2nd order
Conc/Time graph: Half life decreases for zero order, half life stays constant for 1st order, half life increases for 2nd order