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Question

Analyze the objects in this image and write in your science notebook responses to the following guiding questions. Remember to reflect on your understanding of chemical versus physical changes to answer the questions.

Is this an image of a chemical change?
What happens to molecules in each object as they change?
A photo shows separated tobacco leaves exposed to the air in the environment.
These separated tobacco leaves have been exposed to air in the environment.
Source: nnattalli/Shutterstock

Answer 1

In analyzing the image of separated tobacco leaves exposed to the air, we can reflect on the concepts of chemical and physical changes, as well as the behavior of molecules during these processes.

Is this an image of a chemical change?

The exposure of tobacco leaves to air can involve both physical and chemical changes. Initially, when the leaves are separated and dried, this is a physical change. The leaves retain their chemical composition but undergo changes in physical state, such as moisture content. However, over time, exposure to air (oxygen) can lead to chemical changes due to oxidation, which is indicative of a chemical reaction. These changes include the breakdown of compounds and the development of new substances, such as in the fermentation or processes of decay.

What happens to molecules in each object as they change?

1. Physical Changes:

   • When the tobacco leaves are separated and dried, the water molecules within the leaves evaporate. The molecular structure of the tobacco remains the same; only the physical state and moisture content change.
   • If the leaves are stored, physical attributes like texture and color may alter due to drying or environmental exposure, but the leaf’s molecular structure remains unchanged at this stage.

2. Chemical Changes:

   • Upon exposure to air, the tobacco leaves can undergo oxidation. Oxygen molecules from the air react with the compounds in the tobacco, which can lead to changes in flavor and aroma due to the formation of new chemical compounds.
   • Additionally, if the tobacco leaves start to ferment or decompose, microbial action could break down the organic compounds, leading to the production of gases and other products, which signifies a chemical change as the original molecules are transformed into different substances.

In summary, the sequence of events beginning with the physical separation and drying of tobacco leaves followed by potential exposure to air can signify both physical and chemical changes, depending on the specifics of the interactions and processes that occur over time.