(d) A banana turning brown is a chemical change as new, darker (and less tasty) substances form. (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. (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. 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 ( Figure 1.3.3).įigure 1.3.3 (a) Copper and nitric acid undergo a chemical change to form copper nitrate and brown, gaseous nitrogen dioxide. The explosion of nitroglycerin is a chemical change because the gases produced are very different kinds of matter from the original substance. 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. (credit a: modification of work by Tony Hisgett credit b: modification of work by “Atoma”/Wikimedia Commons)Ī chemical change always produces one or more types of matter that differ from the matter present before the change. Nitroglycerin is very dangerous because it explodes easily neon poses almost no hazard because it is very unreactive.įigure 1.3.2 (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. ![]() Iron, for example, combines with oxygen in the presence of water to form rust chromium does not oxidize ( Figure 1.3.2). Examples of chemical properties include flammability, toxicity, acidity, reactivity (many types), and heat of combustion. The change of one type of matter into another type (or the inability to change) is a chemical property. (credit a: modification of work by “95jb14”/Wikimedia Commons credit b: modification of work by “mjneuby”/Flickr) (b) Steam condensing inside a cooking pot is a physical change, as water vapor is changed into liquid water. 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.įigure 1.3.1 (a) Wax undergoes a physical change when solid wax is heated and forms liquid wax. Other examples of physical changes include magnetizing and demagnetizing metals (as is done with common antitheft security tags) and grinding solids into powders (which can sometimes yield noticeable changes in color). We observe a physical change when wax melts, when sugar dissolves in coffee, and when steam condenses into liquid water ( Figure 1.3.1). 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). ![]() 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. We can observe some physical properties, such as density and color, without changing the physical state of the matter observed. Familiar examples of physical properties include density, color, hardness, melting and boiling points, and electrical conductivity. A physical property is a characteristic of matter that is not associated with a change in its chemical composition. ![]() The characteristics that enable us to distinguish one substance from another are called properties.
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