Chemical Weathering

Chemical Weathering Students will be able to: ➢ Define chemical weathering. ➢ Identify agents of chemical weathering. ➢ Describe how chemical weathering causes changes on Earth’s surface. Chemical Weathering Key Vocabulary: ➢ Carbonation ➢ Chemical weathering ➢ Hydrolysis ➢ Oxidation ➢ Weathering Chemical Weathering Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Chemical Weathering Weathering constantly changes the rocky landscape of Earth. It wears away exposed surface over time. Weathering may be categorized as mechanical or chemical. Chemical Weathering Chemical weathering occurs when rocks undergo chemical reactions to form new minerals. Water, acids, and oxygen are just a few of the chemicals that lead to geological change. Over time, chemical weathering can produce dramatic results. Chemical Weathering Chemical weathering involves the weakening and subsequent disintegration of rock by chemical reactions. These reactions include: ➢Oxidation; ➢Hydrolysis; and ➢Carbonation. Chemical Weathering These processes either form or destroy minerals, thus, altering the nature of the rock’s mineral composition. Temperature and moisture are critical for chemical weathering. This is the reason why chemical weathering of rock minerals generally occurs more quickly in hot, humid climatic regions. Chemical Weathering Oxidation is the reaction of rock minerals with oxygen, which results in the changing of the mineral composition of the rock. When minerals in rock oxidize, they become less resistant to weathering. Chemical Weathering An example of oxidation is rust formation, which occurs when oxygen reacts with iron to form iron oxide (rust). Rust changes the color of the rocks, plus iron oxide is much more fragile than iron, so weathered region becomes more susceptible to breakage. Chemical Weathering Water, may it be moving or stagnant, is another agent of chemical weathering. Chemical weathering occurs when water dissolves minerals in a rock, producing new compounds. This reaction is called hydrolysis. Chemical Weathering An example is when water comes in contact with granite. Feldspar crystals inside the granite react chemically, forming clay minerals. The clay weakens the rock, making it more likely to break. Chemical Weathering Water also interacts with calcites in caves, causing them to dissolve. Calcite in dripping water builds up over many years to create stalagmites and stalactites. Chemical Weathering In addition to changing the shapes of rocks, chemical weathering from water changes in the composition of water. For example, weathering over billions of years is a big factor in why the ocean is salty. Chemical Weathering When rocks and minerals are altered by hydrolysis, acids may be produced. One common acid is carbonic acid, a weak acid that is produced when carbon dioxide reacts with water. The process of rock minerals reacting with carbonic acid is known as carbonation. Chemical Weathering Carbonation is an important process in the formation of many caves and sinkholes. Carbonic acid dissolves or breaks down minerals in the rock. Calcite in limestone dissolves under acidic conditions, leaving open spaces. Chemical Weathering Comprehension Check… Answer the following questions. 1. What is chemical weathering? 2. What are the different agents of chemical weathering? 3. Describe how water causes rock minerals to break down chemically. Chemical Weathering Comprehension Check… Answers Answer the following questions. 1. What is chemical weathering? Chemical weathering is the breaking down of rocks through various chemical reactions. 2. What are the different agents of chemical weathering? The agents of chemical weathering are water, oxygen, and acids. 3. Describe how water causes rock minerals to break down chemically. Chemical weathering occurs when water dissolves minerals in a rock, producing new compounds.