Secondary Science - Chemical Change
From Eduwiki
Chemical Change
Many children use the term “chemical change” to address unexpected or unusual changes in physical state such as fizzing, explosions or color change. They do not view a chemical change as a change in properties. Students also hold the misconception that chemical changes are non-reversible. (This is the way my textbook describes chemical changes. The author grouped children’s ideas about chemical change into six main types. 1. No conception – Things just happen that way. 2. Matter just disappears. 3. The products are contained in the starting materials and are just let out. 4. The product is just a modified version of the starting material. 5. The starting material goes through a “transmutation” to the product. 6. The starting materials interact with each other and form a new material.
In order for students to make the distinction between chemical and physical changes, they need to have a strong foundation of what a substance is. For example, if a student does not see ice and water as the same substance, then they will view the melting of ice as a chemical change rather than a physical change. Students who understood substances at the particulate level are more likely to understand the idea of chemical change.
Combustion
While most 11-12 year old's view oxygen as necessary for combustion they do not see it as interacting with the combustible material. Many students view combustion as a faster form of evaporation.
Decomposition
Most students do not recognize decomposition as a chemical change. They view it as a “drying out” of a substance and only the appearance of the substance changes.
Interaction
Many students do not view chemical changes as a mutual reaction between two materials but rather as one material causing the other material to change.
Conservation of Matter Through Change
The concept of fixed masses is very difficult for many students to understand. They often believe that after a chemical reaction the materials will disappear or that the particles in the material become so small that their masses are negligible.
