The highest level of scientific experiment is known as experimental, or randomized control. In this type, as the name implies, there is the greatest amount of control. There are at least two groups used in this type of scientific experiment. Each group is made up of subjects that resemble each other as close as possible, such as by age, gender, etc. Subjects can be human, animal or the environment.
Chemical changes can result from the combination of different substance through a reaction to give one or more different substances. Decomposition, the opposite of combination, involves the breakdown of a single substance into two or more different substances.
Point out to students that this is one of the major characteristics of a chemical reaction: In a chemical reaction, atoms in the reactants combine in new and different ways to form the molecules of the products. Students may be surprised that water can be produced from combustion. In a chemical reaction, the atoms and molecules produced by the reaction are called products. 2  In a chemical reaction, only the atoms present in the reactants can end up in the products. 3  No new atoms are created, and no atoms are destroyed.