In a chemical change, new substances are formed. This is the key difference between chemical and physical changes. Students will need to be aware of the indicators of whether or not a chemical reaction has occurred. In this activity, students will create a spider map identifying and illustrating the signs of a chemical change.
A change in color is a sign that a chemical change might be taking place. An example of a reaction which causes a color change is the rusting of iron. In this reaction, iron reacts with oxygen in the presences of water. The iron oxide that forms is an orange/brown color, different to the gray metallic color of the iron.
If a gas is produced, then a chemical reaction has occurred. A clear sign of this is bubbles in a liquid. This isn’t to be confused with boiling, as boiling is a physical change.
A change in temperature, either an increase or decrease, can indicate a chemical reaction has occurred. When energy is released, the reaction can be described as exothermic. When energy is taken in, the reaction can be described as endothermic.
Sometimes when two liquids are combined, a solid can form. This solid is known as a precipitate and can fall to the bottom or can make the previously clear liquid cloudy.
If there is a noticeable odor after the reaction has occurred, then this could indicate a chemical change has happened. An example of this is milk turning sour.
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Student Instructions
Create a spider map about the indicators of chemical change.