Physical and Chemical Changes

Physical and Chemical Changes
Physical Changes: A physical change refers to a transformation in the appearance or state of matter without altering its chemical composition. In other words, the substance remains the same at the molecular level, even though its physical properties may change. Physical changes are usually reversible.
Examples of physical changes:
Melting Ice: When you heat solid ice, it changes into liquid water. This is a physical change because the substance (water molecules) remains the same; only its state changes.
Boiling Water: When you heat liquid water, it becomes water vapor (steam). Again, this is a physical change as the chemical composition of water remains unchanged.
Crushing a Can: If you crush a soda can, its shape changes, but the material (aluminum) remains the same.
Dissolving Salt: When you mix salt in water, it dissolves. The salt molecules spread out in the water but remain unchanged chemically.
Chemical Changes: A chemical change involves a transformation in which the chemical composition of a substance is altered, resulting in the formation of new substances with different properties. Energy changes often accompany chemical changes and are usually irreversible.
Examples of chemical changes:
Rusting of Iron: When iron reacts with oxygen and moisture in the air, it forms iron oxide (rust)-the composition of the iron changes, leading to a different substance with distinct properties.
Burning Wood: When wood burns, it combines with oxygen in the air and releases heat and light. The original wood molecules break down and form carbon dioxide, water vapor, and ash.
Digestion: When food is digested in our bodies, enzymes break down complex molecules into simpler ones that can be absorbed and utilized. This is a chemical change as the original food molecules are transformed into different substances.
Baking a Cake: When you bake a cake, the ingredients undergo chemical reactions to form a new structure with altered properties. Flour, eggs, and sugar react to create a cake batter that rises and solidifies as it bakes.
In summary, physical changes involve alterations in the state or appearance of matter without changing its chemical composition. In contrast, chemical changes involve the formation of new substances with different properties due to changes in molecular composition.