Question 29

Chopping wood demonstrates a physical change.

Chopping wood is an example of a physical change because it alters the size and shape of the wood without changing its chemical composition. The wood remains wood regardless of how it is chopped; only its physical state is affected.

A) Baking cookies

Baking cookies is a chemical change because it involves a transformation where ingredients react to form new substances, such as the Maillard reaction and the formation of new flavors and textures. This process alters the chemical structure of the ingredients used.

B) Iron rusting

Iron rusting is a chemical change that occurs when iron reacts with oxygen and moisture, forming iron oxide. This process results in a new substance with different properties, indicating a change at the molecular level.

C) Milk becoming sour

Milk becoming sour is also a chemical change. This occurs due to the fermentation process, where bacteria convert lactose into lactic acid, altering the chemical composition and resulting in a different taste and smell.

D) Chopping wood

Chopping wood is a physical change as it modifies the physical form of the wood without affecting its chemical properties. The wood maintains its identity as wood, and the process can easily be reversed by reassembling the pieces.

Conclusion

Chopping wood is definitively the correct answer as it exemplifies a physical change, involving only the alteration of size and shape without changing the wood's chemical identity. In contrast, the other options involve chemical changes where new substances are formed, thus failing to meet the criteria for a physical change.