Download 7.2 NOTES What is chemical weathering? Objective: Explain how

7.2 NOTES
What is chemical weathering?
Objective: Explain how Earth’s surface is worn away by chemical
weathering
In chemical weathering, substances in water cause substances in rocks
to dissolve. This action weakens the rock’s structure over time.
Chemical changes occur when minerals in rocks are broken down into
other substances. They also occur when minerals are added or
removed from rocks. Chemical weathering is usually caused by
reactions with oxygen, water, or acids.
OxidationOxidation occurs when oxygen combines with another substance,
forming oxides. Rust is an iron oxide. Rocks such as pyrite and
magnetite have minerals that contain iron. When exposed to the air,
the iron undergoes oxidation, and the rocks weaken and crumble.
WaterMost chemical weathering is
caused by water. Hydrolysis is a
chemical reaction that occurs
when minerals with little water
content react with water. When
feldspar combines chemically
with water, it changes into clay.
When heated or dried even a
little, the minerals formed by
hydrolysis may fall apart.
AcidsCarbon Dioxide can dissolve in rain to form weak carbonic acid. When
this acid comes in contact with certain minerals, carbonation occurs.
The mineral calcite is changed by carbonation. Two rocks that are
made of calcite
are limestone and
marble. Buildings
made of these
materials are
often weathered
by carbonation.
Some green plants produce weak acids that wear away at rock surfaces.
Decaying organisms also produce acids. The internal structure of
materials that come in contact with these mosses or decayed
organisms will weaken over time.