Chemistry » Essential Ideas in Chemistry » Physical and Chemical Properties

Physical and Chemical Properties

By the end of this lesson and the next, you should be able to:

  • Identify properties of and changes in matter as physical or chemical
  • Identify properties of matter as extensive or intensive

Physical and Chemical Properties

Physical Property

The characteristics that enable us to distinguish one substance from another are called properties. A physical property is a characteristic of matter that is not associated with a change in its chemical composition. Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electrical conductivity.

We can observe some physical properties, such as density and color, without changing the physical state of the matter observed. Other physical properties, such as the melting temperature of iron or the freezing temperature of water, can only be observed as matter undergoes a physical change.

Physical Change

A physical change is a change in the state or properties of matter without any accompanying change in its chemical composition (the identities of the substances contained in the matter). We observe a physical change when wax melts, when sugar dissolves in coffee, and when steam condenses into liquid water (see image below).

physical-change

(a) Wax undergoes a physical change when solid wax is heated and forms liquid wax. (b) Steam condensing inside a cooking pot is a physical change, as water vapor is changed into liquid water. Image credit:- a: modification of work by “95jb14”/Wikimedia Commons; b: modification of work by “mjneuby”/Flickr

Other examples of physical changes include magnetizing and demagnetizing metals (as is done with common anti-theft security tags) and grinding solids into powders (which can sometimes yield noticeable changes in color). In each of these examples, there is a change in the physical state, form, or properties of the substance, but no change in its chemical composition.

Chemical Property

The change of one type of matter into another type (or the inability to change) is a chemical property. Examples of chemical properties include flammability, toxicity, acidity, reactivity (many types), and heat of combustion. Iron, for example, combines with oxygen in the presence of water to form rust; chromium does not oxidize (see image below). Nitroglycerin is very dangerous because it explodes easily; neon poses almost no hazard because it is very unreactive.

chemical-properties

(a) One of the chemical properties of iron is that it rusts; (b) one of the chemical properties of chromium is that it does not. Image credit:- a: modification of work by Tony Hisgett; b: modification of work by “Atoma”/Wikimedia Commons

Chemical Change

To identify a chemical property, we look for a chemical change. A chemical change always produces one or more types of matter that differ from the matter present before the change. The formation of rust is a chemical change because rust is a different kind of matter than the iron, oxygen, and water present before the rust formed. The explosion of nitroglycerin is a chemical change because the gases produced are very different kinds of matter from the original substance.

chemical-changes

(a) Copper and nitric acid undergo a chemical change to form copper nitrate and brown, gaseous nitrogen dioxide. (b) During the combustion of a match, cellulose in the match and oxygen from the air undergo a chemical change to form carbon dioxide and water vapor. (c) Cooking red meat causes a number of chemical changes, including the oxidation of iron in myoglobin that results in the familiar red-to-brown color change. (d) A banana turning brown is a chemical change as new, darker (and less tasty) substances form. Image credit:- a: OpenStax, Chemistry; b: modification of work by Jeff Turner; c: modification of work by Gloria Cabada-Leman; d: modification of work by Roberto Verzo

Other examples of chemical changes include reactions that are performed in a lab (such as copper reacting with nitric acid), all forms of combustion (burning), and food being cooked, digested, or rotting (see image above).

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