Change of Concentration with Time (Section)
(a) The gas-phase decomposition of SO2CI2. SO2CI2(g)→ SO2(g) + CI2(g). is first order in SO2CI2. At 600 K the halflife for this process is 2.3 x 105 s. What is the rate constant at this temperature? (b) At 320 °C the rate constant is 2.2 x 10-5 s-1. What is the half-life at this temperature?
GEOL 101: Weathering and Erosion Interface between climate and Tectonics 1. Weathering – chemical and physical changes that occur in sediments and rocks when they are exposed to the atmosphere and biosphere The process by which rocks are broken down at the earth’s surface to form soil Some rocks weather faster than others NOT EROSION I. Weathering terminology Bedrock – unaltered rock of any kind Rehoboth – a layer of broken pieces of rock and slightly altered rocked that overlays the bedrock o Starting to break down but haven’t moved. Separate bedrock and soil. Soil – a later of altered mineral material usually mixed with organic materials (humus) 2. Erosion – set of processes that losses and transport soil or rock downhill or downwind 3. Transportation 4. Deposition sedimentation 5. Burial 6. Diagenesis changes it from sediment to rock II. Factors that control Weathering Properties of parent rock – different minerals weather at different times Climate – temperature and rainfall Presence or absence of soil – positive feedback Length of exposure Size – smaller rock fragments weather faster than larger rock fragments III. Physical Weathering – Fragmentation of solid rocks by mechanical processes that do not change the chemical Weathering o More common in arid regions Preexisting fractures – natural zones of weakness Frost wedging – water expands by 9% when it freezes o Having water going back and forth between liquid and solid Thermal expansion – differential thermal expansion of minerals creates stress in rocks Organic activity – tree roots to microorgans o Roots grown into faults where the most water and maybe soil is Mechanical abrasion – glaciers, wind, currents IV. Chemical weathering – occurs because mineral formed deep in the earth’s interior are not stable under the conditions on the surface of the earth oThe principal agent of chemical weathering is water oAtmospheric CO2 plays a role Chemical Weathering of Silicate oQuartz – very stable – doesn’t weather oFeldspar – forms clay minerals (kaolinite) oMagic minerals – decomposes to oxides V. Weathering by solution. The complete breakup of minerals into ions in solution Magic silicate dissolve much more slowly than felsic silicates Carbonates – easily soluble in water (especially when acid is present) Sample Exam Questions The greenhouse effect is caused by a. Carbon dioxide and water vapor that trap heat radiating from the earth’s surface b. Heating of homes and businesses, which releases excess hear into the atmosphere c. Oceans that trap heat radiating from the earth’s seafloor d. Too many plants on the surface of the earth , which prevent cooling What is the general process by which rocks are broken down at the earth’s surface A. Deposition B. Erosion C. Lithification D. Weathering Which of the following statements about weathering is false a. Rocks of different compositions weather at different rates. b. Heat and heavy rainfall increase the rate of chemical weathering. c. The presence of soil slows down weathering of the underlying bedrock. d. The longer a rock is exposed at the surface, the more weathered it becomes .