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CHEMICAL WEATHERING

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Akram Suleiman
Akram Suleiman

Chemical weathering is the breakdown of rocks and minerals through chemical reactions with the environment, such as water, air, and organisms. It is influenced by many factors like temperature, climate, surface area exposure, and the presence of water and plants. Chemical weathering breaks down rocks into smaller particles, forms new minerals, and alters chemical compositions through processes like hydrolysis, oxidation, and ion exchange. It shapes landscapes over thousands of years and influences soil and water resources.

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CHEMICAL WEATHERING 1 Done by : - Majed Abdelrahim Alsmadi / 0188539 - Omar Sami Alkouz / 0206775 - Omar Ahmad Almhareb / 0195206 https://www.youtube.com/watch ?v=uSi6DWbWL1U
Introduction: 2 Chemical weathering is a natural process whereby rocks and minerals are transformed through chemical reactions with various elements in the environment such as water, air, and organisms. This process occurs as a result of multiple factors including temperature, pressure, and the presence of acidic or alkaline substances. The effects of chemical weathering can lead to a range of alterations in rocks and minerals including the formation of new minerals, the breakdown of minerals into smaller particles, and changes in their chemical composition. This natural process has significant impacts on the environment, contributing to the formation of geological features like canyons, mountain ranges, and caves while also influencing soil quality and water sources.
Introduction: 3 Chemical weathering is primarily caused by slightly acidic water. As raindrops fall through the air, they dissolve atmospheric carbon dioxide: H2O + CO2 S H2CO3 Rainwater thus is a weak solution of carbonic acid (H2CO3)like Perrier water! When weakly acidified rainwater becomes soil water or groundwater, it may dissolve additional carbon dioxide from decaying organic matter, becoming more strongly acidified. Another way that rainwater can become acidified is by interacting with anthropogenic (human-generated) sulfur and nitrogen compounds released into the atmosphere. This produces a phenomenon called acid rain. Human-caused acid rain is stronger than natural acid rain and causes accelerated weathering.
Introduction: 4 Through dissolution, minerals can be completely removed without leaving a residue. Some common rock-forming minerals, such as calcite (calcium carbonate) and dolomite (calcium magnesium carbonate), dissolve in slightly acidified water.
Introduction: 5 Water can also alter the mineral content of rock without dissolving all of it. One reaction of special importance in chemical weathering is ion exchange. Ions, which have a positive or negative electric charge, exist both in solution and in minerals. They form when atoms give up or accept electrons . Ions in minerals are tightly bonded and fixed in a crystal lattice, but ions in solutions can move about randomly and cause chemical reactions. Ion exchange is important in a common chemical weathering process known as hydrolysis, in which hydrogen ions (H+) released from acidic water enter and alter a mineral by displacing larger positively charged ions such as potassium (K+), sodium (Na+), and magnesium (Mg2+) (Figure 1). This type of weathering alters the composition of both the minerals and the water solutions that fill the pore spaces and fractures in the rock. Where do the potassium and other ions go after they are replaced by hydrogenions? Some remain in the groundwater, accounting for the taste of mineral water that some people find pleasant and others do not, and some flow out to sea and form part of the oceans reserve of dissolved salts. On the other hand, if the water evaporates, the dissolved materials can precipitate out again as solid evaporites, such as halite and gypsum.
Introduction: 6 Ion exchange . Figer-1
7
8 Chemical weathering is, basically, a surface phenomenon; therefore, the greater the surface area exposed, the more intense the reaction
Surface area : 9 The extent and pace of chemical weathering are significantly influenced by the surface area of rocks and minerals. Generally, the higher the surface area, the quicker the weathering process occurs. This is due to the fact that chemical reactions take place at the surface of the rock or mineral. If a rock is broken into smaller pieces, the total surface area of the rock will increase, which provides more space for chemical reactions, causing it to weather faster. The surface area effect is also relevant to many practical applications, such as the use of limestone in construction or the mining of ore deposits. In these cases, the amount of exposed surface area can affect the efficiency and effectiveness of industrial processes that involve chemical reactions. Additionally, the shape of the rock also affects the weathering rate; rocks with uneven surfaces, such as those with cracks and crevices, weather more quickly than those with smoother surfaces. Understanding the surface area effect is crucial in predicting and comprehending the extent and speed of chemical weathering.
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Factor of water in chemical weathering: 11 Water is one of the most important factors in chemical weathering. It plays a crucial role in facilitating chemical reactions that break down rocks and minerals. Water is a universal solvent, meaning it can dissolve a wide range of substances, and it can penetrate deep into rocks and minerals to promote chemical reactions. One of the most common forms of chemical weathering that occurs in the presence of water is hydrolysis. Hydrolysis occurs when water reacts with minerals in rocks to break them down into new compounds. For example, feldspar minerals can undergo hydrolysis in the presence of water to form clay minerals and dissolved ions. Another way that water can contribute to chemical weathering is through oxidation reactions. Water is necessary for the oxidation of iron-bearing minerals, such as pyrite and magnetite, which react with oxygen to form iron oxides.
Factor of water in chemical weathering: 12 Water can also increase the rate of chemical weathering by promoting the growth of microorganisms that aid in the breakdown of rocks and minerals. In some cases, microorganisms can produce acids that dissolve minerals, leading to increased weathering rates. The impact of water on chemical weathering can be seen in many natural landscapes, such as canyons and river valleys, where water has played a significant role in shaping the landscape over time. Understanding the role of water in chemical weathering is crucial for predicting and managing the impact of weathering on natural environments and human-made structures.
Factor of plants in chemical weathering: 13 Plants can also play an important role in chemical weathering, particularly through their ability to produce organic acids that can dissolve minerals in rocks. These acids are produced by the roots of plants as they extract nutrients from the soil. The organic acids can dissolve minerals such as calcium carbonate, which is found in limestone, and contribute to the weathering of rocks and minerals. In addition to producing organic acids, plants can also contribute to weathering through their physical action on rocks. As roots grow and expand, they can exert pressure on rocks, causing them to crack and break. This process, known as root pry, can expose more surface area of rocks to chemical weathering agents such as water and oxygen. Furthermore, plants can help to create and sustain microenvironments that support the growth of microorganisms that contribute to chemical weathering. For example, the roots of plants can create spaces within rocks that provide a suitable habitat for microorganisms to live and thrive.
Factor of plants in chemical weathering: 14 The role of plants in chemical weathering is especially important in areas with significant vegetation cover, such as forests and grasslands. In these ecosystems, the combination of organic acid production, root pry, and microorganism activity can lead to significant weathering of rocks and minerals over time. In summary, plants can contribute to chemical weathering through the production of organic acids, root pry, and the creation of microenvironments that support the growth of microorganisms. Understanding the role of plants in chemical weathering is important for predicting and managing the impact of weathering on natural environments.
15
Effect of climate : 16 Climate is an important factor in chemical weathering. High levels of rainfall, warm and humid temperatures, and the abundance of water can increase the rate of chemical weathering. In contrast, arid regions may experience more physical weathering processes. The type of climate also influences the type of chemical weathering that occurs. Understanding the impact of climate on weathering processes is crucial for predicting the long-term effects of weathering on natural environments and human- made structures.
Effect of climate : 17 Climate affects the rate of weathering in two different ways. As noted earlier, chemical weathering is more intense and extends to greater depths in a warm, wet, tropical climate than in a cold, dry, arctic climate. In cold, dry climates, such as in Greenland or Antarctica, chemical weathering proceeds very slowly. On the other hand, mechanical weathering is fairly rapid in these harsh environments. The only environment where both kinds of weathering proceed very slowly is a hot, dry climate (Figure 2). - 2
18 Classification of Weathering Grade
Classification of Weathering Grade 19 Weathering leads to a general disintegration of rock through changes in mineral composition, increase in void space, and weakening of interparticle bonds . The degree of disintegration depends on the original composition and texture of the rock, as well as the processes and rates of weathering, Depending upon the degree of weathering, the engineering properties of weathered rock can be significantly different compared to fresh rock. Therefore, the engineering description of a rock must include a description of its degree or grade of weathering in both qualitative and quantitative terms.
Classification of Weathering Grade 20 Based on visual observations, the Geological Society of London (1995) proposed six grades of weathering (Table-1) : Table-1
CHEMICAL WEATHERING
In conclusion, chemical weathering is an important geological process that occurs over long periods of time, resulting in the breakdown of rocks and minerals. Factors such as surface area, water, plants, and climate all play crucial roles in promoting chemical weathering. Understanding these factors and their impacts is important for predicting and managing the effects of weathering on natural environments and human-made structures. Overall, chemical weathering is a complex and dynamic process that contributes to the shaping of the Earth's surface over time. 22
23 References: - Visualizing Geology by Barbara W. Murck (Book) - https://www.accessscience.com/content/article/a743100 (Article in site) - Geology: A Very Short Introduction by Jan Zalasiewicz (Book) - PRINCIPLES OF GEOLOGY BY CHARLES 揃 LYELL, ESQ. F. R. S (Book) - https://education.nationalgeographic.org/resource/weathering/ (Article in site)

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CHEMICAL WEATHERING

  • 1. CHEMICAL WEATHERING 1 Done by : - Majed Abdelrahim Alsmadi / 0188539 - Omar Sami Alkouz / 0206775 - Omar Ahmad Almhareb / 0195206 https://www.youtube.com/watch ?v=uSi6DWbWL1U
  • 2. Introduction: 2 Chemical weathering is a natural process whereby rocks and minerals are transformed through chemical reactions with various elements in the environment such as water, air, and organisms. This process occurs as a result of multiple factors including temperature, pressure, and the presence of acidic or alkaline substances. The effects of chemical weathering can lead to a range of alterations in rocks and minerals including the formation of new minerals, the breakdown of minerals into smaller particles, and changes in their chemical composition. This natural process has significant impacts on the environment, contributing to the formation of geological features like canyons, mountain ranges, and caves while also influencing soil quality and water sources.
  • 3. Introduction: 3 Chemical weathering is primarily caused by slightly acidic water. As raindrops fall through the air, they dissolve atmospheric carbon dioxide: H2O + CO2 S H2CO3 Rainwater thus is a weak solution of carbonic acid (H2CO3)like Perrier water! When weakly acidified rainwater becomes soil water or groundwater, it may dissolve additional carbon dioxide from decaying organic matter, becoming more strongly acidified. Another way that rainwater can become acidified is by interacting with anthropogenic (human-generated) sulfur and nitrogen compounds released into the atmosphere. This produces a phenomenon called acid rain. Human-caused acid rain is stronger than natural acid rain and causes accelerated weathering.
  • 4. Introduction: 4 Through dissolution, minerals can be completely removed without leaving a residue. Some common rock-forming minerals, such as calcite (calcium carbonate) and dolomite (calcium magnesium carbonate), dissolve in slightly acidified water.
  • 5. Introduction: 5 Water can also alter the mineral content of rock without dissolving all of it. One reaction of special importance in chemical weathering is ion exchange. Ions, which have a positive or negative electric charge, exist both in solution and in minerals. They form when atoms give up or accept electrons . Ions in minerals are tightly bonded and fixed in a crystal lattice, but ions in solutions can move about randomly and cause chemical reactions. Ion exchange is important in a common chemical weathering process known as hydrolysis, in which hydrogen ions (H+) released from acidic water enter and alter a mineral by displacing larger positively charged ions such as potassium (K+), sodium (Na+), and magnesium (Mg2+) (Figure 1). This type of weathering alters the composition of both the minerals and the water solutions that fill the pore spaces and fractures in the rock. Where do the potassium and other ions go after they are replaced by hydrogenions? Some remain in the groundwater, accounting for the taste of mineral water that some people find pleasant and others do not, and some flow out to sea and form part of the oceans reserve of dissolved salts. On the other hand, if the water evaporates, the dissolved materials can precipitate out again as solid evaporites, such as halite and gypsum.
  • 7. 7
  • 8. 8 Chemical weathering is, basically, a surface phenomenon; therefore, the greater the surface area exposed, the more intense the reaction
  • 9. Surface area : 9 The extent and pace of chemical weathering are significantly influenced by the surface area of rocks and minerals. Generally, the higher the surface area, the quicker the weathering process occurs. This is due to the fact that chemical reactions take place at the surface of the rock or mineral. If a rock is broken into smaller pieces, the total surface area of the rock will increase, which provides more space for chemical reactions, causing it to weather faster. The surface area effect is also relevant to many practical applications, such as the use of limestone in construction or the mining of ore deposits. In these cases, the amount of exposed surface area can affect the efficiency and effectiveness of industrial processes that involve chemical reactions. Additionally, the shape of the rock also affects the weathering rate; rocks with uneven surfaces, such as those with cracks and crevices, weather more quickly than those with smoother surfaces. Understanding the surface area effect is crucial in predicting and comprehending the extent and speed of chemical weathering.
  • 10. 10
  • 11. Factor of water in chemical weathering: 11 Water is one of the most important factors in chemical weathering. It plays a crucial role in facilitating chemical reactions that break down rocks and minerals. Water is a universal solvent, meaning it can dissolve a wide range of substances, and it can penetrate deep into rocks and minerals to promote chemical reactions. One of the most common forms of chemical weathering that occurs in the presence of water is hydrolysis. Hydrolysis occurs when water reacts with minerals in rocks to break them down into new compounds. For example, feldspar minerals can undergo hydrolysis in the presence of water to form clay minerals and dissolved ions. Another way that water can contribute to chemical weathering is through oxidation reactions. Water is necessary for the oxidation of iron-bearing minerals, such as pyrite and magnetite, which react with oxygen to form iron oxides.
  • 12. Factor of water in chemical weathering: 12 Water can also increase the rate of chemical weathering by promoting the growth of microorganisms that aid in the breakdown of rocks and minerals. In some cases, microorganisms can produce acids that dissolve minerals, leading to increased weathering rates. The impact of water on chemical weathering can be seen in many natural landscapes, such as canyons and river valleys, where water has played a significant role in shaping the landscape over time. Understanding the role of water in chemical weathering is crucial for predicting and managing the impact of weathering on natural environments and human-made structures.
  • 13. Factor of plants in chemical weathering: 13 Plants can also play an important role in chemical weathering, particularly through their ability to produce organic acids that can dissolve minerals in rocks. These acids are produced by the roots of plants as they extract nutrients from the soil. The organic acids can dissolve minerals such as calcium carbonate, which is found in limestone, and contribute to the weathering of rocks and minerals. In addition to producing organic acids, plants can also contribute to weathering through their physical action on rocks. As roots grow and expand, they can exert pressure on rocks, causing them to crack and break. This process, known as root pry, can expose more surface area of rocks to chemical weathering agents such as water and oxygen. Furthermore, plants can help to create and sustain microenvironments that support the growth of microorganisms that contribute to chemical weathering. For example, the roots of plants can create spaces within rocks that provide a suitable habitat for microorganisms to live and thrive.
  • 14. Factor of plants in chemical weathering: 14 The role of plants in chemical weathering is especially important in areas with significant vegetation cover, such as forests and grasslands. In these ecosystems, the combination of organic acid production, root pry, and microorganism activity can lead to significant weathering of rocks and minerals over time. In summary, plants can contribute to chemical weathering through the production of organic acids, root pry, and the creation of microenvironments that support the growth of microorganisms. Understanding the role of plants in chemical weathering is important for predicting and managing the impact of weathering on natural environments.
  • 15. 15
  • 16. Effect of climate : 16 Climate is an important factor in chemical weathering. High levels of rainfall, warm and humid temperatures, and the abundance of water can increase the rate of chemical weathering. In contrast, arid regions may experience more physical weathering processes. The type of climate also influences the type of chemical weathering that occurs. Understanding the impact of climate on weathering processes is crucial for predicting the long-term effects of weathering on natural environments and human- made structures.
  • 17. Effect of climate : 17 Climate affects the rate of weathering in two different ways. As noted earlier, chemical weathering is more intense and extends to greater depths in a warm, wet, tropical climate than in a cold, dry, arctic climate. In cold, dry climates, such as in Greenland or Antarctica, chemical weathering proceeds very slowly. On the other hand, mechanical weathering is fairly rapid in these harsh environments. The only environment where both kinds of weathering proceed very slowly is a hot, dry climate (Figure 2). - 2
  • 19. Classification of Weathering Grade 19 Weathering leads to a general disintegration of rock through changes in mineral composition, increase in void space, and weakening of interparticle bonds . The degree of disintegration depends on the original composition and texture of the rock, as well as the processes and rates of weathering, Depending upon the degree of weathering, the engineering properties of weathered rock can be significantly different compared to fresh rock. Therefore, the engineering description of a rock must include a description of its degree or grade of weathering in both qualitative and quantitative terms.
  • 20. Classification of Weathering Grade 20 Based on visual observations, the Geological Society of London (1995) proposed six grades of weathering (Table-1) : Table-1
  • 22. In conclusion, chemical weathering is an important geological process that occurs over long periods of time, resulting in the breakdown of rocks and minerals. Factors such as surface area, water, plants, and climate all play crucial roles in promoting chemical weathering. Understanding these factors and their impacts is important for predicting and managing the effects of weathering on natural environments and human-made structures. Overall, chemical weathering is a complex and dynamic process that contributes to the shaping of the Earth's surface over time. 22
  • 23. 23 References: - Visualizing Geology by Barbara W. Murck (Book) - https://www.accessscience.com/content/article/a743100 (Article in site) - Geology: A Very Short Introduction by Jan Zalasiewicz (Book) - PRINCIPLES OF GEOLOGY BY CHARLES 揃 LYELL, ESQ. F. R. S (Book) - https://education.nationalgeographic.org/resource/weathering/ (Article in site)