Physical and Chemical Changes

  In the video “Chemical Changes: Crash Course Kids #19.2,” two examples of physical changes and two examples of chemical changes are discussed. Let’s explore these examples and explain why they are classified as physical or chemical changes. Physical Change: Melting Ice When ice melts, it undergoes a physical change. The solid ice (H2O) transitions into liquid water (H2O) without any change in the chemical composition. The molecules of H2O remain the same, but their arrangement changes from a solid state to a liquid state. This change is reversible, meaning that if the liquid water is frozen again, it will become solid ice. Physical Change: Tearing Paper When a paper is torn into smaller pieces, it is considered a physical change. The paper’s chemical composition remains the same, and no new substances are formed. The paper is simply being physically separated into smaller fragments. This change can also be reversed by reassembling the torn pieces. Chemical Change: Burning Wood When wood is burned, it undergoes a chemical change. The complex organic compounds present in wood, such as cellulose and lignin, react with oxygen in the air through combustion. This reaction releases energy in the form of heat and light and transforms the wood into ash and gases (such as carbon dioxide and water vapor). The chemical composition of wood is altered during this process, resulting in the formation of new substances. Chemical Change: Rusting of Iron When iron comes into contact with oxygen and moisture over time, it undergoes a chemical change known as rusting. The iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide, commonly known as rust. This chemical reaction changes the composition of the iron, resulting in the formation of a new compound. In summary, physical changes involve alterations in physical properties or states of matter without changing the chemical composition of a substance, while chemical changes involve the formation of new substances with different chemical compositions. Melting ice and tearing paper are examples of physical changes, as they only affect physical properties or states, whereas burning wood and rusting iron are examples of chemical changes, as they involve the formation of new substances through chemical reactions.  

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