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Within this section, Matter and Its Interactions Portfolio Apply, analyze the images on the following 2 pages. In the first image, you will see a tobacco leaf as it changes from green to brown; in the second image you will observe a chemist pouring a fuel liquid into a test tube that causes a small explosion to occur, and in the last image, a person is holding a piece of gallium metal as it melts from a solid into liquid metal. Reflect on your understanding of chemical versus physical changes to answer each question. Which of these images shows a chemical change? What happens to molecules in each object as they change? Write it in a students level.

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In this section, we are looking at images that show different changes in materials, and we need to determine which ones show chemical changes and which ones show physical changes.

  1. Tobacco Leaf Changes from Green to Brown: This image shows a physical change. The green color of the tobacco leaf changes to brown as it dries out. This is primarily due to the breakdown of chlorophyll, the pigment that makes leaves green. Even though the color changes, the molecules that make up the leaf itself haven’t changed in their structure. They are still the same molecules; they just look different.

  2. Chemist Pouring Fuel into a Test Tube: This image shows a chemical change. When the chemist pours the fuel and it causes a small explosion, this is a chemical reaction. During this reaction, the molecules of the fuel combine with oxygen to create new substances, such as gases and heat. The original molecules are transformed into completely different molecules.

  3. Gallium Melting from Solid to Liquid: This image shows a physical change. Gallium is a metal that can melt in your hand because it has a low melting point. When it melts, the solid gallium becomes liquid gallium. The molecules in gallium do not change; they just move apart and allow the substance to flow when it melts. The identity of the substance remains unchanged.

Summary:

  • Chemical Change: The chemist pouring fuel, as it changes into new substances.
  • Physical Changes: The tobacco leaf changing color and gallium melting. In these cases, the molecules stay the same, but their arrangement or state changes.