Chemical reactions occur all around us and can be observed with the naked eye.
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
The image that shows a chemical change is the second image, where the chemist pours a fuel liquid into a test tube that causes a small explosion to occur.
In a chemical change, the molecules of the substances involved rearrange themselves to form new substances with different chemical compositions. This typically involves the breaking and forming of chemical bonds. In the second image, the fuel liquid reacts with some other substance in the test tube, resulting in the explosion. This indicates a chemical change has occurred.
In the first image, the tobacco leaf changing from green to brown is a physical change. The molecules within the leaf remain the same, but the arrangement and properties of the molecules change as the leaf undergoes chemical reactions, such as oxidation, causing it to change color.
In the last image, the person holding a piece of gallium metal as it melts from a solid into liquid metal represents a physical change. The molecules of gallium remain the same during the phase change, only the arrangement and movement of the molecules change as they transition from a solid state to a liquid state.
The second image, which shows a chemist pouring a fuel liquid into a test tube that causes a small explosion, represents a chemical change. In a chemical change, the molecules of substances involved break and reform bonds, resulting in the formation of new substances with different chemical properties.
In the first image, where the tobacco leaf changes from green to brown, it represents a physical change. In a physical change, the molecules of the substance remain the same, but their arrangement or state may change.
In the last image, where a person is holding a piece of gallium metal as it melts from a solid into liquid metal, it also represents a physical change. The molecules of gallium remain the same throughout the process of melting, but their arrangement changes from a tightly packed solid structure to a less ordered liquid structure.