The starting material or materials for a chemical reaction are referred to as the reactants. The substance or substances produced from a chemical reaction are called products. Sometimes a secondary product, a byproduct, can also be created at the same time as the desired product(s). Not every chemical reaction occurs in the same way. There are different types of chemical reactions, including synthesis reactions, decomposition reactions, and displacement reactions. In this experiment, a decomposition reaction takes place. During a decomposition reaction, a compound breaks apart into two or more products. Most decomposition reactions need an outside source of energy in order to take place. Hydrogen peroxide is not a very stable compound, so it slowly decomposes into water and oxygen gas under normal conditions. In this reaction, yeast is used as a catalyst. A catalyst is a substance that helps to change the rate of a reaction. During the reaction, the catalyst is not consumed. As a result, the yeast makes the reaction occur much faster; it causes the hydrogen peroxide to break down and release the oxygen gas much faster. The soap is used to help us “see” the reaction. Bubbles of oxygen become trapped in the soap, creating foam. The reaction occurs so quickly, releasing so much gas and creating so much foam, that the foam begins to flow out of the bottle. The result of this reaction looks like toothpaste being squeezed out of a tube. In addition, the bottle will feel warm to the touch because the reaction is exothermic. An exothermic reaction or process is one that gives off energy. In contrast, an endothermic reaction or process is one that requires or absorbs energy. HYPOTHESIS uAdding yeast to hydrogen peroxide will cause the hydrogen peroxide to decompose quickly into water and oxygen gas, creating foam as the gas becomes trapped in liquid dish soap and pushes upward out of the bottle. FORMULAS & EQUATIONS Hydrogen peroxide is a relatively clear liquid substance. It is soluble in water and is often sold as a mixture of H2O2 in water. The hydrogen peroxide used in this experiment is actually a 6% solution of H2O2 in water. The chemical formula for hydrogen peroxide is H2O2. Hydrogen peroxide naturally decomposes into water and oxygen gas. The reaction is shown by the following equation: 2H2O2 (aq)g2H2O (l) + O2 (g) The rate of the reaction can be increased by introducing a catalyst. In this experiment, the catalyst is yeast. Yeast is a microorganism that is part of the fungi family. Therefore, in the equation below, the catalyst is indicated above the arrow. yeast 2H2O2 (aq) g 2H2O (l) + O2 (g) The hydrogen peroxide used in the experiment is actually a mixture of water and hydrogen peroxide. CONNECT TO THE YOU BE THE CHEMIST CHALLENGE For additional background information, please review CEF’s Challenge study materials online at http://www.chemed.org/ybtc/challenge/study.aspx. • Additional information on elements, compounds, and physical and chemical changes can be found in the Classification of Matter section of CEF’s Passport to Science Exploration: The Core of Chemistry. • Additional information on chemical reactions can be found in the Chemical Reactions section of CEF’s Passport to Science Exploration: Chemistry
Density: The molecules of a liquid are packed relatively close together. Consequently, liquids are much denser than gases. The density of a liquid is typically about the same as the density of the solid state of the substance.
In a gas, the distance between molecules, whether monatomic or polyatomic, is very large compared with the size of the molecules; thus gases have a low density and are highly compressible. In contrast, the molecules in liquids are very close together, with essentially no empty space between them
