1.5:
Physical and Chemical Properties of Matter
Characteristics that help us to distinguish one type of matter from another are referred to as properties. Matter exhibits two types of properties: physical and chemical.
Physical properties of matter can be measured and observed without changing the composition or identity of the matter. Odor, taste, color, appearance, hardness, density, melting and boiling points, and electrical conductivity, are all examples of physical properties.
Some of these physical properties can be observed without changing the physical state of the matter. So, when we say that helium gas is lighter than air, we are referring to a physical property. Similarly, the smell of gasoline is also a physical property.
Other physical properties can only be observed when matter undergoes physical changes. For example, pure gold in its solid-state is made up of tightly packed gold atoms. But when it is melted at a high temperature, it changes its state from a solid to a liquid. However, this liquid is still composed of gold atoms, so this is a physical change.
Similarly, when liquid water freezes to solid ice, the chemical composition of both the water and ice remains the same. Thus, physical changes only alter the state of the matter or physical conditions, without changing the chemical composition.
Crushing, grinding, slicing, blending, magnetizing, or demagnetizing are other common ways to change the physical condition of matter.
Chemical properties of matter, on the other hand, are characteristics that can only be measured and observed when the substance has a change in chemical composition. Corrosiveness, flammability, toxicity, acidity, or chemical reactivity are all examples of chemical properties of matter.
In order to identify a chemical property, we look for a chemical change. Chemical changes involve chemical reactions and are often observed through a change in color or odor.
For example, when a copper penny is exposed to air and water there is a chemical change. The copper undergoes a series of chemical reactions, one of which is shown here, to form a layer of blue-green patina on an otherwise naturally brown penny.
Thus, chemical changes produce entirely new forms of matter which differ from the matter present before the change. For instance, the flammability of gasoline is a chemical property evident from the chemical changes in the composition of gasoline when it burns, turning gasoline into entirely new substances, primarily carbon dioxide and water.
1.5:
Physical and Chemical Properties of Matter
The characteristics that enable us to distinguish one substance from another are called properties.
Physical Properties of Matter
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 the water, can only be observed as matter undergoes a 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, for example, wax melts, sugar dissolves in coffee, and steam condenses into liquid water. Other examples of physical changes include magnetizing and demagnetizing metals (as is done with common anti-theft security tags) and grinding solids into powders. 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 Properties of Matter
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. Nitroglycerin is very dangerous because it explodes easily; neon poses almost no hazard because it is very unreactive.
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. 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), the ripening of fruits, and food being cooked, digested, or rotting.
This text is adapted from Openstax, Chemistry 2e, Section 1.3: Physical and Chemical Properties.