What do all chemical reactions have in common? Most students describe a chemical reaction as an event where an explosion, color change, or a gas is formed. As a prerequisite for this lesson students need only be acquainted with the particulate nature of matter. The main learning objective is the recognition that all chemical reactions create new molecules and that in a chemical reaction the original atoms get rearranged, bonding together in different ways. Overall, the lesson will take about 45-55 minutes. During the first two breaks, the class will list their preconceptions about chemical reactions and then experience an exciting reaction which is produced inside a re-sealable plastic bag. The chemicals needed for this reaction are sodium bicarbonate and calcium chloride. After this excitement, the video will show how to separate the mixture to demonstrate the existence of the new products, which include sodium chloride, CO2 and chalk. The separation can be completed by the classroom teacher as well at a later time. In the third break, the teacher will write out the balanced chemical equation and the class will account for the same number of atoms on each side of the equation, demonstrating the conservation of mass. In the fourth break, students will have time to model the atoms chemical reaction using LEGO® bricks as the atoms or by using atoms made from clay or homemade play dough. Lastly, the video will apply the definition of chemical reaction to analyze a scene where a cork explodes from a heated liquid in a test tube.
For more information, visit: http://blossoms.mit.edu/videos/lessons/recognizing_chemical_reactions