Folding paper is a classic concept used to teach the fundamental properties of matter. The action demonstrates how materials can be altered without changing their core identity. Folding a piece of paper is definitively a physical change.
Distinguishing Physical and Chemical Changes
The scientific classification of changes in matter relies on whether the identity of the substance is altered during the process. A physical change affects the form or appearance of a substance but leaves its chemical structure unchanged. Simple examples include boiling water, where liquid H2O turns into gaseous H2O, or cutting a wire into smaller pieces. These changes are often easily reversible.
A chemical change, by contrast, involves a transformation where a new substance with a different chemical composition and new properties is formed. This change occurs when chemical bonds are broken and new bonds are created between atoms. Common indicators that a chemical change has taken place include the production of light or heat, a permanent color change, or the formation of a gas or a solid precipitate. Chemical reactions are generally harder to reverse than physical changes.
Why Folding Paper is a Physical Change
The act of folding paper only alters its shape and size, which are physical properties. Paper is primarily composed of cellulose, a long-chain polymer of glucose molecules. When a crease is formed, the cellulose molecules themselves remain chemically intact.
The change is considered physical because the material remains paper, even in its folded state. Unfolding the paper, while leaving a permanent crease, still results in the original material. The crease forms because the plant fibers along the fold are pushed beyond their elastic limit, causing a permanent physical deformation. This process simply rearranges the microscopic fibers within the paper’s structure.
Other Ways Paper Changes
Other mechanical manipulations of paper, such as tearing or shredding, are also classified as physical changes. Tearing only reduces the size and changes the shape of the paper, but the shredded pieces are still composed of the same cellulose polymer. No new substance is created during the tearing process.
A contrast is seen when paper is burned, which is an example of a chemical change called combustion. When paper is ignited, the cellulose reacts vigorously with oxygen in the air. This chemical reaction breaks the molecular bonds in the cellulose and forms entirely new compounds: ash, carbon dioxide gas (CO2), and water vapor (H2O). The resulting ash and gases possess chemical properties distinct from the original paper, and the change is irreversible.