Some good observations . The bumpy surface is the real reason for the fantastic reaction between the coke and the mentos.
Think about the coke. It is a fizzy drink. How has it become fizzy? In the making process a lot of gas (Carbon Dioxide) is dissolved in the coke under high pressure . Water has lots of air dissolved in it. There are quite a few liquids that can absorb gases.
So what happens when the mentos is dropped into the coke? It’s all to do with surface. If the mentos had a completely smooth surface, like the inside of the coke bottle very little would happen (you can test this). However look at the image above, the mentos tablet is covered with valleys and holes. Each of these sharp points is a place where a bubble of the gas absorbed in the coke can attach itself to and therefore remove itself from the coke liquid.
The gas bubble is lighter than the liquid coke, so what does it do? It moves upwards (it’s lighter than the liquid so it floats). Millions of bubbles begin to move upwards. What is in their way? Coke liquid.
There are lots of things to investigate here. Start doing some science. Do shiny things create bubbles? Do the number of mentos tablets increase the explosive effect? How can you measure it fairly? Does the temperature of the coke affect what occurs.
Have fun but test the ideas that I have presented you with. Science can be fun. If you want to ask another question, do it. If you or any other reader would like to make a comment use the ‘Leave a Reply’ box below.
Sorry I forgot one of your original questions. The bubble forming and bubble emission processes are physical and not chemical processes.