Science Buddies: "Ask an Expert"

Hello. I am in 8th grade and at my school we must do a science fair project. My project is about the relation between Mentos and coke. I will test whole and crushed Mentos and measure the time of the reaction and how much soda is left over in the bottle. For this science fair we must interview an expert. I have seen online that there has been some arguement of whether the reaction of Mentos and coke is a physical reaction or chemical reaction. So I would like to know your opinion of whether you think it is a physical or chemical reaction. It would be greatly appreciated if you could reply as soon as possible.Thank you.

Hi CitlalliG,

The Mentos and coke experiment is a physical reaction rather than a chemical reaction. Inside a bottle of coke, there is dissolved carbon dioxide gas which is what makes the soda fizzy when you drink it. Normally you can find these gas bubbles coming out of solution on the sides of the bottle, and that is why soda becomes flat after being opened for a while. However, this process is quite slow. Adding Mentos causes this process to speed up, because the bubbles form more easily on the surface of the Mentos than on the side of the bottle. Since the addition of Mentos is just speeding up a physical process (i.e. the carbon dioxide gas coming out of solution), the reaction is a physical reaction. This is a state change for the carbon dioxide gas from being dissolved in Coke to a gaseous state.

In order for the reaction to be a chemical reaction, the chemicals inside of the coke or the Mentos needs to change. In this case the only thing that's changing is the state of matter of the carbon dioxide.

I hope this helps with your project and good luck!

If you have any additional questions feel free to ask.
Stephen Lee