2 (h.b.a) Oxygen in Earth's Atmosphere
Oxygen: Oxygen is called an element, because it is made of the same kinds of atoms (oxygen atoms). Almost all of our oxygen in our atmosphere was made by producers through a process called photosynthesis. Oxygen Even though oxygen is the second most abundant gas in the atmosphere, it makes up less than one fourth of the volume. Plants and animals take oxygen directly from the air and use it to release energy from their food. Oxygen is also involved in many other important processes. Any fuel you can think of, from the gasoline in a car to the candles on a birthday cake, uses oxygen as it burns. Without oxygen, a fire will go out. Burning uses oxygen rapidly. During other processes, oxygen is used slowly. For example, steel in cars and other objects reacts slowly with oxygen to form iron oxide, or rust. Chemical change A change in matter that produces one or more new substances is a chemical change, or a chemical reaction. In other chemical changes, two or more substances combine to form different substances. For example, iron metal combines with oxygen from the air to form the substance iron oxide, which you call rust. Unlike a physical change, a chemical change produces new substances with properties different from those of the original substances. The chemical change that occurs when fuels such as natural gas, wood, candle wax, and gasoline burn in air is called combustion.