K – Grade 3 students
Have you ever had a cut and had your parent or a nurse put hydrogen peroxide on it? The hydrogen peroxide reacts with iron in your blood to form oxygen bubbles, the gas that we breathe. The formation of bubbles is similar to what would happen if you blew air into a bubble bath using a straw. The formation of bubbles on your cut was a chemical reaction. The liquid hydrogen peroxide was being converted into liquid water and oxygen gas. Liquids and gases are two of the three phases of matter with solids being the third kind. Oxygen is a new substance formed in this chemical reaction and it has different properties than the original hydrogen peroxide. We cannot make the gas oxygen go back to become liquid hydrogen peroxide because a chemical reaction has occurred. Did you notice your cut becoming warm when the hydrogen peroxide was poured onto it? This reaction of hydrogen peroxide releases energy in the form of heat. Atoms of hydrogen and oxygen are rearranging how they are connected to one another.
Grade 4 – 5 students
At this grade level, students know that all matter is made up of atoms and that the atoms in the reactants rearrange to form products with different properties during chemical reactions. They also know that an element is made of one kind of atom and that the elements are organized in the periodic table by their chemical properties. Students are aware of the properties of solid, liquid, and gaseous substances.
When hydrogen peroxide interacts with either beef liver or yeast, a biological molecule in the yeast or beef liver called an enzyme causes hydrogen peroxide molecules to react to form a water molecule and an oxygen molecule. Hydrogen peroxide contains two hydrogen and two oxygen atoms while water contains two hydrogens and one oxygen atom. Two molecules of hydrogen peroxide each lose an oxygen atom which combine to form oxygen gas, which contains two oxygen atoms. Oxygen is a gas and is the elemental form of the eighth element in the periodic table. Both water and hydrogen peroxide are compounds, which are substances made up of one or more elements.
During the reaction between hydrogen peroxide and beef liver or yeast, a large amount of heat is released. You may have experienced this reaction if you ever had a parent or nurse put hydrogen peroxide on an open cut. Heat is created by reactions when bonds between atoms are formed or broken down. When the hydrogen peroxide breaks down into water and oxygen, the reaction gives off heat because the bonds in the hydrogen peroxide have broken apart and released some of their energy in the form of heat.
Middle school students
At this grade level, students will have a better understanding of life science and will be able to understand the concepts of enzymes and catalysts. They also know how energy can be moved around within a reaction and how energy can be transferred from the reaction to the environment. They should also understand that energy can be measured by the temperature of an object and the environment.
Have you ever hurt yourself and had a parent clean the cut out with hydrogen peroxide? If you have, then you would have seen the bubbles that form as soon as the liquid makes contact with your cut. The creation of bubbles is a direct result of the hydrogen peroxide and an enzyme in your tissue called catalase breaking down the bacteria in the cut. Catalase is a catalyst that helps break down the hydrogen peroxide but also helps speed up the reaction. Although nothing extra happens due to a catalyst, it makes the reaction go faster by lowering the energy needed to react. We use beef liver instead of yeast for this experiment because it is a better catalyst and makes the reaction happen much faster.
When a reaction takes place, bonds are being broken apart or put together. Much like how magnets willingly come together and struggle to separate. It requires energy to change these bonds and it can be shown in the form of heat. As a reaction absorbs energy to break a bond, you will see the temperature around the reaction cooling. Opposite to that, when the reaction releases energy from the bond, the temperature around it begins to heat up.
College-level/ scientific description
In this experiment, the catalytic decomposition of hydrogen peroxide results in the formation of oxygen gas and water. This means catalase, a protein catalyst found in beef liver and yeast, works with the liver or yeast to break apart the hydrogen peroxide. This catalyst reduces the activation energy needed for the reaction and also helps to speed up the reaction rate and make the reaction go much faster.
The reaction also heats up meaning this is an exothermic reaction. When reactions take place and bonds are broken or created, the bond energies for the reactants and products are a factor in whether the reaction releases or consumes energy. In this experiment, the bond energies of the products (water and oxygen) are much greater than that of the reactant (hydrogen peroxide). This means the reaction releases energy and is measured in the form of heat.