Change: Chemical Change
Evidence: The reaction of baking powder involves a chemical reaction that produces carbon dioxide gas, altering the composition of the ingredients involved. The release of gas causes the dough to rise and results in the formation of new substances, meaning the original components (flour, sugar, butter, etc.) undergo a transformation that cannot be reversed simply by physical means. The change in texture and volume of the dough further confirms that a chemical change has occurred.
Example 2: Rusting of Iron
Change: Chemical Change
Evidence: When iron is exposed to oxygen and moisture over time, it reacts to form iron oxide, commonly known as rust. This process alters the chemical composition of the iron, creating a new substance that is less durable than the original metal. The formation of rust can be observed as a reddish-brown flaky substance on the surface, indicating a permanent change that cannot be reversed just by removing the rust. The process also weakens the structural integrity of the iron, further demonstrating that a chemical change has occurred.
Example 3: Dissolving Sugar in Water
Change: Physical Change
Evidence: When sugar is dissolved in water, it breaks down into smaller particles and interacts with water molecules, creating a solution. However, no new substances are formed, and this process can be reversed by evaporating the water to retrieve the original sugar. The physical properties of the sugar and water can be restored, indicating that this is a physical change rather than a chemical one.
Example 4: Burning Wood
Change: Chemical Change
Evidence: Burning wood involves a reaction between wood (cellulose) and oxygen, producing ash, carbon dioxide, and water vapor. This irreversible process changes the chemical structure of the wood, resulting in new substances that differ from the original. The release of energy in the form of heat and light during combustion also supports that a chemical change has taken place.
Example 5: Melting Ice
Change: Physical Change
Evidence: When ice melts, it transforms from a solid to a liquid state (water). This change is reversible; if the water is frozen again, it will become ice once more. The chemical composition of water (H₂O) remains unchanged throughout this process. The change in state from solid to liquid indicates a physical change rather than a chemical one.