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Decide whether a physical or chemical change has occurred and give evidence for your decision. The first one has been done for you to use as an example.

In baking biscuits and other quick breads, the baking powder reacts to release carbon dioxide bubbles. The carbon dioxide bubbles cause the dough to rise.

11 answers

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.

in baking biscuits and other quick breads, the baking powder reacts to release carbon dioxide bubbles. The carbon dioxide bubbles cause the dough to rise.

Change: Chemical Change

Evidence: In baking biscuits and other quick breads, the baking powder undergoes a chemical reaction when it is combined with moisture and heat. This reaction produces carbon dioxide gas, which forms bubbles in the dough. The release of carbon dioxide not only causes the dough to rise, but it also indicates that a new substance is being formed (carbon dioxide) from the ingredients in the baking powder. The resulting changes in texture and volume are evidence that the composition of the dough has changed permanently, confirming that this is a chemical change rather than a physical one.

You take out your best silver spoons and notice that they are very dull and have some black spots.

Change: Chemical Change

Evidence: The dull appearance and black spots on the silver spoons are indicative of tarnishing, which occurs when silver reacts with sulfur compounds in the air or other substances, forming silver sulfide. This reaction alters the surface of the silver, resulting in a new substance that is different from the original shiny silver. The black spots (tarnish) cannot simply be removed by wiping them away; they often require cleaning with specific silver polish or chemical treatments to restore the original luster. This transformation demonstrates that a chemical change has occurred, as new substances have been formed through the reaction with the environment.

A straight piece of wire is coiled to form a spring.

Change: Physical Change

Evidence: When a straight piece of wire is coiled to form a spring, the process involves a change in shape and arrangement of the wire but does not alter its chemical composition. The metal (typically steel or another alloy) remains the same both before and after coiling. Since the wire can be uncoiled back into its original straight form without any change to its chemical properties, this indicates that a physical change has occurred. The elasticity and structure of the wire are modified, but the material of the wire itself remains unchanged.

Food color is dropped into water to give it color.

Change: Physical Change

Evidence: When food color is dropped into water, it disperses and colors the water without altering the chemical composition of either the food color or the water itself. The process is reversible; if the colored water is left to evaporate, the food color can be concentrated and eventually recovered. The primary change here is in the physical state and appearance of the water, while the substances involved retain their original chemical properties. This indicates that a physical change, rather than a chemical change, has occurred.

Chewing food to break it down into smaller particles represents a _________ change, but the changing of starch into sugars by enzymes in the digestive system represents a ___________change.

Chewing food to break it down into smaller particles represents a physical change, but the changing of starch into sugars by enzymes in the digestive system represents a chemical change.

Explanation: Chewing food physically breaks it down into smaller pieces, making it easier to digest, but does not alter its chemical structure. In contrast, the action of enzymes converting starch into sugars involves a chemical reaction that changes the chemical composition of the starch, resulting in new substances (sugars).