Physical and Chemical Properties/States of Matter

The properties of a substance are those characteristics that are used to identify or describe it. When we say that water is "wet", or that silver is "shiny", we are describing materials in terms of their properties. Properties can be divided into the categories of physical properties and chemical properties. Physical properties are readily observable, like; color, size, luster, or smell. Chemical properties are only observable during a chemical reaction. For example, you might not know if sulfur is combustible unless you tried to burn it.

Another way of separating kinds of properties is to think about whether or not the size of a sample would affect a particular property. No matter how much pure copper you have, it always has the same distinctive color. No matter how much water you have, it always freezes at zero degrees Celsius under standard atmospheric conditions. Methane gas is combustible, no matter the size of the sample. Properties, which do not depend on the size of the sample involved, like those described above, are called intensive properties. Some of the most common intensive properties are; density, freezing point, color, melting point, reactivity, luster, malleability, and conductivity.

Extensive properties are those that do depend on the size of the sample involved. A large sample of carbon would take up a bigger area than a small sample of carbon, so volume is an extensive property. Some of the most common types of extensive properties are; length, volume, mass and weight.

Pieces of matter undergo various changes all of the time. Some changes, like an increase in temperature, are relatively minor. Other changes, like the combustion of a piece of wood, are fairly drastic. These changes are divided into the categories of Physical and Chemical change. The main factor that distinguishes one category form the other is whether or not a particular change results in the production of a new substance.

Physical changes are those changes that do not result in the production of a new substance. If you melt a block of ice, you still have H2O at the end of the change. If you break a bottle, you still have glass. Painting a piece of wood will not make it stop being wood. Some common examples of physical changes are; melting, freezing, condensing, breaking, crushing, cutting, and bending. Special types of physical changes where any object changes state, such as when water freezes or evaporates, are sometimes called change of state operations.

Chemical changes, or chemical reactions, are changes that result in the production of another substance. When you burn a log in a fireplace, you are carrying out a chemical reaction that releases carbon. When you light your Bunsen burner in lab, you are carrying out a chemical reaction that produces water and carbon dioxide. Common examples of chemical changes that you may be somewhat familiar with are; digestion, respiration, photosynthesis, burning, and decomposition.




http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson15.htm