Mentos and Coke With "Geyser Tube"

This is great fun with friends and family.  It never seems to get old!

Materials

    2 liter of diet soda (any soda will work but diet doesn't leave a sticky mess behind)
    Mentos
    Safety goggles
    Geyser tube* (sold at stores or at stevespanglerscience.com)

*Optional geyser tube is recommended but not needed.  The tube allows for a high spray of the soda in a narrow flow.  Also you have less of a chance to get drenched with the soda!  If you use the "geyser tube", please follow directions on the packaging.

Procedure Without "Geyser Tube"

    Find a flat surface
    Put on safety glasses to protect eyes
    Open diet soda and place on flat surface.
    Open up mentos container
    Insert mentos into bottle
    Move away quickly

Procedure Using "Geyser Tube"

     Find a flat surface
     Put on safety glasses
     Open diet soda and place on flat surface
     Secure tube on to bottle
     Insert pin to stop mentos from falling
     Remove top of tube
     Place around seven mentos into tube
     Replace top of tube
     Gently move back with string in hand (string is connected to pin)
     Pull string to release pin
     Stand back and enjoy the show

The Science

The mentos has tiny indents all over its surface. These are called nucleation sites. Carbon dioxide from the soda build up in these spots, forming bubbles.  The mentos sinks and the the bubbles rise.  What is in the way of the bubbles?  Liquid.  The bubbles rising to the top force the liquid out the bottle in an awesome eruption!  Now would this be a chemical reaction?  Why or why not?