Friday, September 16, 2016

Chemical Properties of Matter


In addition to physical properties like hardness, malleability, and melting point, matter has properties related to how they are arranged at the molecular level. Chemical properties can only be observed when a substance interacts with other substances and changes.

Chemical Properties:
  • any ability to produce change in the composition of matter at the molecular level.
  • can only be observed when the substances in a sample of matter change into different substances.

A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected greatly for its chemical properties to be investigated. When a substance goes under a chemical reaction, the properties will change drastically, resulting in chemical change. (https://en.wikipedia.org/wiki/Chemical_property)

Two chemical properties are flammability and reactivity.

Flammability
Flammability is a material's ability to burn in the presence of oxygen.

Burning is a chemical reaction in which molecules of the flammable substance combine with oxygen and give off energy that causes the air nearby to glow and give off light (flame).

Reactivity
Reactivity is the property that describes how readily a substance combines chemically with other substances.

Substances react with other substances in different ways. Some things are highly reactive and others are not. Oxygen is an example of something that reacts easily. Nitrogen is an example of something that does not.


Chemical Changes
Chemical changes (which rely on chemical properties) occur when a substance reacts with another substance and forms one or more NEW substances that are different in molecular composition compared to the original substances. For example…

Many people know that water is chemically represented by H2O. This notation means that two molecules of hydrogen chemically combine with one molecule of oxygen to make up a molecule of water. So, to form water, two substances, hydrogen and oxygen, chemically react, and the NEW substance is water. Water is different from both the hydrogen and oxygen that form it..

When chemical changes occur, there are usually physical changes and often other signs of the change.

A Change in Color
Many chemical changes result in the new substance showing a different color then the original.

Production of Gas
Some reactions release gas, and can be observed as bubbles or an odor.

Formation of a Precipitate
In liquid mixtures, chemical reactions will often cause the newly formed substances to take on a solid form and suspend more obviously in the liquid. The solid that forms in a liquid mixture is called a precipitate. The precipitate may remain suspended in the liquid, may settle to the bottom, or may float to the top.

Temperature Change

It is not uncommon for chemical changes to involve a temperature change. When a chemical change gives off heat (the system gets warmer), it is said to be exothermic. When a chemical change takes in heat (the system cools off), it is said to be endothermic.

It is not always easy to tell if an observed change is physical or chemical. A heated piece of iron will change color, but still be iron. Gas bubbles will form when water's temperature approaches its boiling point, but it is still water.

For a chemical change to take place, two or more substances must change at the molecular level to become one or more NEW substances.


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Definitions and content from:
New Oxford American Dictionary
Physical Science Concepts in Action, Pearson
http://en.wikipedia.org

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