Two classes of substances well known for combining readily, and sometimes violently, are acids and bases. The chemicals that make up these groups vary dramatically, but all those in each group have important characteristics in common. Acids are characterized by a tendency to produce positively charged hydrogen ions. Bases, in contrast, produce negatively charged hydroxide ions, comprised of one oxygen atom and one hydrogen atom.
When acidic and basic solutions are combined, the acid's positive ions and the base's negative ions react to form water and release heat energy. The remaining elements combine to form various other compounds, depending on the chemical makeup of the acid and base involved.
Some acid-base reactions produce carbon dioxide, a gas that is a potentially powerful propellant when under pressure. When lemon juice and baking soda are combined in a sealed bottle, they react to form water, sodium ions, and carbon dioxide. As the carbon dioxide concentration builds up inside the bottle, the pressure inside the bottle also increases. If the pressure becomes high enough, it can propel the stopper out of the opening of a bottle and across a great distance.
The fact that the bottle rocket demonstrated in this ZOOM video segment jumps off of the table just after the stopper shoots into the air is explained by an important law of physics, Newton's third law of motion. This law states that every action has an equal and opposite reaction. This means that when we push against a wall, the wall, even though it is inanimate, pushes back on us with an equal amount of force.
When the pressure inside the bottle builds up enough and the stopper blasts from the opening of the bottle rocket, the bottle pushes against the carbon dioxide and forces it out. As Newton's third law predicts, the carbon dioxide pushes back on the bottle and pushes it down into the table. Although the bottle can't go far before it meets the table's surface, its plastic construction allows it to compress slightly. As the downward force subsides, the bottle snaps back into shape, causing it to bounce off the table's surface.