What is chemical weathering? Mr. White Earth Science

Learning Objective Students will explain how Earth's surface is worn away by chemical weathering.

Key Terms oxidation carbonation hydrolysis

Kinds of Chemical Weathering In chemical weathering, substances in water cause substances in rocks to dissolve. This action weakens the structure of the rocks. Chemical changes occur when minerals in rocks are broken down into other substances. They also occur when minerals are added to or removed from rocks. Chemical weathering is usually caused by reactions with oxygen, water, or acids.

The Statue of Liberty contains a large amount of copper The Statue of Liberty contains a large amount of copper. Its thin copper skin reacts with oxygen in the air to form a green coating.

Oxidation One kind of chemical weathering is oxidation. Oxidation occurs when oxygen combines with another substance. New substances called oxides are formed. Rust is an iron oxide.

Like copper statues, rocks can be oxidized. Oxidized rocks change color. Here, the iron in the rock has reacted with oxygen in the air. The red streaks are oxidized iron, or rust.

Water Most chemical weathering is caused by water. Water reacting chemically with a mineral that has little water content is called hydrolysis. Many minerals in rocks undergo hydrolysis. For example, feldspar may combine chemically with water and change to clay. When heated or dried even a little, minerals formed by hydrolysis may fall apart.

Acids Carbon dioxide can dissolve in rain to form weak carbonic acid. When this acid comes into contact with certain minerals, a chemical change called carbonation occurs. The mineral calcite is changed by this process. Limestone and marble are made of calcite. Buildings made of these materials are often weathered by carbonation.

Many buildings and building decorations are made of limestone. Limestone can be damaged by carbonation.

Organisms Some green plants produce weak acids. Mosses, which grow on rocks, are an example. The acids can wear away a rock's surface. As acid seeps into cracks in a rock, it can break the rock apart. Decaying organisms also produce acids, which contribute to chemical weathering.

Checking Concepts What process will most likely chemically weather an iron-rich rock? What substances cause most chemical weathering?

Answers Oxidation Oxygen, water and acids

The End