A Thruster You Can Touch
1Each spring, the aerospace club at Brightwater Middle School runs a table at the public library's Space Day. This year, club members Oluwaseun Adebayo and Mira Halvorsen-Cruz wanted to show how some real rockets and spacecraft thrusters have used hydrogen peroxide. In those engines, very concentrated hydrogen peroxide flows over a catalyst, a substance that speeds up a reaction without being used up. The peroxide breaks down into water vapor and oxygen gas, the reaction releases a large amount of thermal energy, and the hot gases rush out of a nozzle.
2The club's model uses much safer materials: drugstore hydrogen peroxide solution, which is mostly water, and dry baker's yeast, which contains a natural catalyst. The reaction is 2 H₂O₂ → 2 H₂O + O₂. Oxygen bubbles foam up inside an open 1-liter plastic bottle that stands on a tray, and the liquid warms up. The club adviser, Ms. Ayumi Hayashi, mixes the yeast with water and pours it into the peroxide. Everyone at the table wears goggles and gloves, and no flames are allowed nearby.
3The club set four criteria for the model. The liquid must reach at least 30 °C, so visitors can clearly feel the warm bottle. It must stay at or above 30 °C for at least 3 minutes, long enough for a line of visitors to touch it. The foam must stay inside the bottle. Each demonstration may use no more than 250 mL of peroxide solution, so the club's supplies last the whole day.
4In Test 1, the club changed the concentration of the peroxide. The drugstore solution is 3% hydrogen peroxide, meaning 3 g of hydrogen peroxide in every 100 g of solution. Ms. Hayashi mixed some of it with water to make 2% and 1% solutions. Every trial used 100 mL of solution at 20 °C and 5 g of yeast mixed into 20 mL of water at 20 °C. A temperature probe in the liquid recorded the highest temperature and the number of minutes at or above 30 °C. The club ran each test three times and recorded the averages.
5In Test 2, they kept the 3% solution and changed the amount, using 5 g of yeast for every 100 mL of solution. All of the solutions in both tests started at 20 °C.