The student prompt is, “Write an informative essay comparing physical and chemical change. Include evidence from the text and experiments for both types of changes.
The essay should contain both an introductory and closing paragraph. The body should contain at least two paragraphs—one paragraph that addresses physical change and provides evidence for the physical change, and one paragraph that addresses chemical change and provides evidence for the chemical change. Based on information students would have recorded in their science notebooks, the teacher actually develops an answer to the prompt that a successful student might provide. Following is an example:
Matter has properties by which it can be described. These include physical properties like size, shape, color, density and boiling point. Matter can also be described by its chemical properties that enable it to react with other matter to create new substances. These properties include its valence electrons, toxicity, flammability, chemical stability.
The properties of matter can change both physically and chemically. A physical change involves a change in the physical properties, but not in the matter itself. The text, page 248, describes a physical change as “a type of change in which the form of matter is altered but one substance is not transformed into another.” For example, in our experiments we learned that a physical change occurs when paper is torn. The pieces of paper are smaller, but it is still paper. Another example from our experiment is phase changes. Water can be liquid, solid or a gas, but it is still water.
A chemical change occurs when two types of matter combine to form a new substance. The text, on page 250, describes a chemical change as, “a process where one or more substances are altered into one or more new and different substances.” We also learned from our reading and our discussions that chemical reaction involves the re-arrangement of atoms and molecules to make new substances, but the amount of matter stays the same. From our experiments, we learned about different indicators of a chemical reaction. If a gas or precipitate is formed, it is a chemical reaction. For example, baking soda and vinegar form a gas that was not present until the two substances were combined. Another indicator of a chemical reaction is a change in temperature or a change in color. Baking soda, calcium chloride and water give off heat when combined. We found an example outside of the classroom of chemical change when we looked at leaf that was changing colors from green to orange.
The next time you observe matter, determine its properties. Then try to change it. If it stays the same matter, it is a physical change. But if you can create something new, it is a chemical change.