Physical changes do not produce new substances, but chemical changes do produce new substances. A physical change is concerned with states of matter. Melting, vaporization, freezing, sublimation and condensation are physical changes. Melting an ice cube is a physical change because the substance remains as water. Most physical changes are reversible. Crushing a can, boiling water, breaking glass, chopping wood, mixing sand and water, and shredding paper are physical changes.
Chemical changes occur on the molecular level. The change produces a new substance. Chemical changes include combustion, synthesis, oxidation, neutralization and decomposition. For example, iron rusting is an instance of a chemical change. Food metabolism, burning wood, mixing and acid with a base, baking a cake and using a chemical battery are also examples of chemical changes.
A chemical change can be determined by evaluating if a reaction has occurred. A chemical reaction may have occurred if a change in light, heat, color, gas production, odor or sound is produced. If a precipitate develops, then a chemical change has occurred. An odor is a sign of a chemical change because it is evidence that decomposition is occurring. For example, a rotten egg produces an odor as it transforms into a new substance.Learn More
Examples of chemical changes include burning of wood, digestion of sugar, an exploding firecracker, reactions between salts and acids and lighting a matchstick. A chemical change involves changes at the atomic and molecular level.Full Answer >
The term "chemical reaction" refers to any process that changes a set of chemical substances to another. That is, the substances that are put into a chemical reaction are different, on a molecular level, from those that result.Full Answer >
Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place. Both of these two mechanisms of chemical change involve the heat characteristics of the involved substance or substances and the environment in which the chemical change is taking place.Full Answer >
Phosphorus is a nonmetal solid that comes in three forms: black, white and red. White phosphorus can spontaneously ignite and is poisonous. The element has an atomic weight of 31 and atomic number of 15, and its atomic symbol is P.Full Answer >