Bkng soda vinegar is a CHEMICAL reaction, a chemical change occurs giving CO2 and water. The rate depends on the conc. of your vinegar, temperature and the surface area of the soda (fine powder)

Mentos/coke is a PHYSICAL reaction, no chemical change occurs (though sugar dissolves and eventually hydrolyses to glucose, but this is incidental). The same thing happens with Mentos and carbonated water.

CO2 dissolved in the coke is released by a process called nucleation on the surface of the mentos.

A rough surface is better than a smooth one, so this might be a useful area to investigate for your project.

The mentos reaction is probably fastest under most conditions, and you can experiment with temperature, acid strength, different types of Mentos (some are smooth and are rubbish), fizzy drinks with different amounts of sugar dissolved, lots of variables are there if you think about it.

Mentos is a brand of mints, of the "scotch mint" type, sold in many markets across the world by the Perfetti Van Melle Corporation. Mentos was first produced in the Netherlands during the 1950s. The mints are small oblate spheroids, with a slightly hard exterior and a soft, chewy interior. They are sold in rolls which typically contain 14 candies, although the new "Sour Mix" flavor contains only 11 candies per roll. Certain flavors are sold in boxes in the United States and the United Kingdom, and the rolls in three and six-packs. The slogan of Mentos is "The FreshMaker." Most Mentos packages describe the candy as "chewy dragées." The typical Mentos roll is approximately 3/4-inch in diameter, 6/16-inches tall and 1.3 ounces.

First popularized by Steve Spangler on 9News in 2005, which resulted in Internet coverage of the incident,[1] a Mentos mint expedites a rapid release of carbon dioxide when dropped into a carbonated liquid, such as a soft drink, because of its high surface tension. Also, the small dents in the surface of the candy provide a great site for nucleation, which is how the carbon dioxide molecules can escape so rapidly. The escaping bubbles quickly turn into a raging foam, and the pressure can build dramatically in a restricted container such as a two-liter bottle. As Jamie Hyneman and Adam Savage, special mechanical effects experts who have come to be known as "The MythBusters," explained on an episode of MythBusters (Episode 57, Season 4; "Mentos and Soda," aired on August 9, 2006), diet sodas (particularly colas due to their visible brown color) are most commonly used for the experiment. The MythBusters also found that the fruit flavored Mentos produced a smaller reaction, supporting their theory that nucleation is the largest factor in the reaction, because the wax coating blocks the pits that allow nucleation. People are often under the illusion that aspartame causes the reaction--this is only partly true; the MythBusters have shown aspartame to be one of many reactive components and/or catalysts in both the soda and the Mentos. Diet colas are also preferred because they do not contain large amounts of sugar like regular colas. Sugar molecules help keep the carbon dioxide in solution, slowing the reaction. Artificial sweeteners in diet colas are much sweeter per molecule, and so make up a smaller proportion of the solution and allow a faster reaction; they also enhance the reaction. The resulting geyser (popularly known as a "Diet Coke and Mentos eruption") can shoot as high as 6 meters (20 ft). The record, reached in MythBusters, was over 34 feet with the use of a nozzle. On July 10, 2007, a record number Mentos-and-Diet Coke geysers, 791, were set off in Flower Mound, Texas by employees of Books Are Fun and the company's independent representatives. Guinness World Records had a representative in attendance, who confirmed the feat. On July 15, 2007, a world record was set in Perfetti Van Melle's hometown of Breda, North Brabant, The Netherlands, in which 850 people set off Mentos-and-Diet Coke geysers at the same time. Everyone put five pieces of Mentos in the Coke at the same time producing geysers of four to five meters high. The record will be included in the Guinness World Records.[citation needed] On April 23, 2008, students in the Belgian city of Leuven set a new world record, simultaneously launching 1,360 Mentos geysers. Besides making geysers with cola and Mentos, the bottles can also be fired as rockets by unscrewing the lid until a thin stream shoots and slamming horizontally into the ground, creating enough pressure on impact to blast the lid off and launch the bottle in the opposite direction. These work best when the bottle is shaken for about 20 seconds vigorously after quickly putting in the Mentos. It takes a few practices to work out how much to twist the lid off (usually approximately one full turn) but can travel large distances with this technique, often up to 20ft high and between 40-70ft horizontally.In November, 2006, the Urban Legends Reference Pages examined the rumors of people dying from eating Mentos and drinking cola. Their research found that while eating Mentos and drinking cola can result in people regurgitating the foamy result (as evidenced by numerous online videos), no actual news accounts exist of anyone dying from it.