Properties and Changes in Matter
Every substance, whether an element or compound, has characteristic properties. Chemists use these properties to distinguish different substances and then use their knowledge of characteristics to separate them.
A property may be a characteristic that defines an entire group of substances. That property can be used to classify an unknown substance within that group. For example, are large groups of elements is metals. The property that sets than apart from anything else is that they conduct electricity well. Therefore, if scientists find an unknown element, and test it for electricity conduction, and it turns out to conduct electricity well, it is, in fact, a metal.
Properties also define subgroups or substances. And can also help to reveal the identity of an unknown substance. However, identification usually cannot be made based on only one property. Comparisons of several properties can be used to determine the identity of an unknown. Properties are either intensive or extensive. An extensive property depends on the amount of matter that is present. These properties include volume, mass, and the amount of energy in a said substance. Intensive properties, however, do not depend on the amount of matter present. These properties include the melting point, boiling point, density, and ability to conduct electricity and heat. Regardless of how much of a substance is present, these properties will always be the same.
Chemical and Physical Properties and Changes
Physical Properties and Physical Changes
A physical property is a characteristic that can be measured or observed without changing the identity of the substance. Physical properties describe the substance itself. Examples of these properties are properties such as melting point and boiling point.
A change in a substance that does not involve a change in the identity of the substance is called a physical change. Examples of physical changes include grinding, gutting, melting, and boiling a substance or material. These changes do not change the physical identity of a property. For example: If you rip a paper in half, does that change the identity of the two torn parts? The answer is no, it is still a paper, just smaller and ripped. If you bend a paper clip, is it still a paper clip? Yes.
Melting point and boiling point are part of an important classification of physical changes called change of state. A change of state is a physical change of a substance from on state to another. The three common states of matter are solid, liquid, and gas. Matter in the solid shape has a definite volume and definite shape. Matter in the liquid state has a definite value, but not a definite shape-a liquid can be molded or formed into many different shapes. Matter in the gas state has neither definite volume nor definite shape.
Chemical Properties and Chemical Changes
Physical properties can be observed without changing the identity of the substance, but chemical properties cannot. A chemical property relates to a substances ability to undergo changes that transform it into different substances. Chemical properties are easiest to see when substances react to form (a) new substance(s). For example, when charcoal burns, it combines with oxygen in air to become a new substance, carbon dioxide gas. After this chemical change, the original substances of the charcoal, carbon and oxygen, are no longer present. Another example is the ability of iron to rust by combining with oxygen in the air (moisture).
A change in which one or more substances are converted into different substances is called a chemical change or reaction. The substances that react in a chemical change are called the reactants. The substances formed by the chemical change are called the products. By burning charcoal, carbon and oxygen are the reactants in a combustion, or burning reaction. Carbon dioxide is the product.
Chemical changes and reactions, such as combustion and decomposition, form products whose properties differ greatly from those of the reactants. Chemical changes, however, do not affect the total amount of matter present before and after a reaction. The amount of matter, and total mass, remain the same.