Explanation: In this demonstration, we will be showing the reaction between vinegar (acetic acid) and baking soda (sodium bicarbonate) to produce carbon dioxide gas. This is a simple and safe chemical reaction that can be easily performed in a classroom setting.

Materials needed: - Vinegar - Baking soda - Clear plastic bottle - Balloon - Funnel

Safety precautions: - Wear safety goggles to protect your eyes from any splashes. - Perform the demonstration in a well-ventilated area to avoid inhaling any fumes. - Do not ingest any of the chemicals used in the demonstration. - Keep a fire extinguisher nearby in case of any accidents.

Step-by-step guide: 1. Place the clear plastic bottle on a flat surface. 2. Using a funnel, pour a small amount of vinegar into the bottle, filling it about one-third of the way. 3. Take the balloon and stretch the opening to make it easier to fit over the mouth of the bottle. 4. Add a spoonful of baking soda to the balloon using the funnel. 5. Carefully stretch the opening of the balloon over the mouth of the bottle, making sure it is securely in place. 6. Once the balloon is attached, lift it up slightly to allow the baking soda to fall into the vinegar. 7. Watch as the reaction occurs, causing the balloon to inflate as carbon dioxide gas is produced. 8. Discuss with the students the chemical reaction that took place, emphasizing the formation of carbon dioxide gas and the importance of balancing chemical equations.

By following these steps and safety precautions, you can safely demonstrate a simple chemical reaction to high school students, helping them understand key principles of chemistry in a hands-on way.