Chemical Weathering
CHEMICAL WEATHERING Process by which rocks break down as a result of chemical reactions.
CHEMICAL WEATHERING chemical reactions Process by which rocks break down as a result of chemical reactions. Dissolve minerals in rocks or change them into different minerals.
Agents of chemical weathering 1. Water 2. weak acids (acid precipitation, acids in ground water, acids in living things) 3. air. These agents weaken bonds between the mineral grains of rock.
Water Can cause rock to be broken down and dissolve. Can take thousands of years to take place.
Dissolves minerals from a rock over a long period of time (sometimes 1000s of years). 1. Water
2. Weak Acids Include acid precipitation acids in ground water acids in living things
Acid precipitation Where does acid rain come from? Rain, sleet, or snow, that contains a high concentration of acids. Small amounts of nitric or sulfuric acids from volcanoes. Air pollution from fossil fuels (coal & oil) give off gases & combines with water to from acid rain.
Acid Precipitation (weak acid) Rain, sleet, or snow that contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal.
Acid Rain Compounds from burning coal, oil and gas react chemically with water forming acids. Acid rain causes very rapid chemical weathering
Some groundwater contains weak acids like carbonic & sulfuric acid. These weak acids react with rocks, causing a chemical reaction. Ex. When groundwater touches limestone, it dissolves limestone to form caves over thousands of years. Acids in Ground water
Acids in Groundwater (weak acid) Carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock.
Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble
National Geographic Photos
Acids in Living Things (weak acid) Lichens produce acids that slowly break down rock.
Acids in Living things Lichens produce acids that slowly break down rock Roots and decaying plants release acids that dissolve minerals, thus weakening the rock.
AIR The process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust. Weak Acids
Oxygen in the air reacts with iron, causing it to rust (called oxidation). This process is called oxidation. A chemical reaction in which an element (iron) combines with oxygen to cause rust. Causes aluminum cans, bikes, & cars to rust. Water speeds up this process. 3. Air oxidation
Karst Topography A type of landscape in rainy regions where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams. Created by chemical weathering of limestone
Features of Karst: Sinkholes
Features of Karst: Caves
Features of Karst: Disappearing Streams
Quick Check Which of the following things cannot cause mechanical weathering? A. water B. acids C. wind D. animals
Quick Check Which of the following is a type of frost action? A. abrasion B. oxidation C. ice wedging D. gravity
Quick Check Which of the following types of chemical weathering causes a karst landscape, such as a cavern? A. lichens B. acid precipitation C. acids in groundwater D. water
Quick Check How do lichens slowly break down a rock? A. by abrasion B. by mechanical means C. by ice wedging D. by chemical means
Quick Check Which of the following will most likely experience oxidation? A. tennis ball B. aluminum can C. wooden fence D. Bicycle tire