Download Ch 6 Exam Review - Perry Local Schools

Ch 6 Exam Review
Major Concepts:
Rocks and minerals are disintegrated and decomposed by the processes of mechanical and chemical weathering.
This breakdown occurs because the parent material reacts with its new physical and chemical environment
transforming it into a new equilibrium state.
The products of weathering include soluble salts, ions in solution, and solid particles which can be eroded and
become sedimentary rock or modified in place to become soils.
Mechanical weathering includes the processes of frost action, pressure release, thermal expansion and
contraction, crystal growth, and the activities of organisms. The products of mechanical weathering are chemically
the same as their parent materials.
Chemical weathering processes include solution, oxidation, and hydrolysis. These processes cause a change in
the chemical composition whereby parent material is transformed into products including ions in solution, soluble
salts and clay minerals.
Hot and wet environments accelerate chemical weathering. Chemical weathering occurs in all environments,
except, possibly, permanently frozen polar regions.
Mechanical weathering enhances chemical weathering by breaking material into smaller pieces, thereby
increasing the surface area for chemical reactions.
Possible Essay Questions:
How do exfoliation domes form? Where would you go to see examples?
ANSWER: Exfoliation domes form in rocks prone to expansion and the formation of expansion joints. Deeply
buried rock bodies, such as plutons, expand as they are uplifted and eroded. Plutonic rock bodies that
exhibit exceptional exfoliation domes include Half Dome, in Yosemite National Park, California, and
Stone Mountain, Georgia.
Why is thermal expansion and contraction not a particularly effective type of mechanical weathering on Earth?
ANSWER: Thermal expansion and contraction may not occur due to the lack of extreme temperatures (hot and
cold) occurring with enough frequency on Earth to be an effective type of weathering. In addition, the
forces produced may not be as significant as a result.
What are the similarities between the mechanical weathering processes called frost wedging and salt crystal growth?
ANSWER: Both frost wedging and salt crytal growth involve expansive forces resulting from crystal growth, the
former case involving the growth of ice crystals. In both cases, an expansive force is produced.
Why is rainfall naturally acidic?
Rainfall (H20) falls through an atmosphere that is contains carbon dioxide (CO2). The reaction of water and
carbon dioxide results in an acid called carbonic acid (H 2CO3)
Briefly explain why water is such an important agent in weathering.
ANSWER: For chemical weathering, water is necessary for hydrolysis and the formation of carbonic acid. Water
serves to hold and transport the dissolved products. The expansion of water upon freezing, salts dissolved
in water, its support of organic growth all facilitate the mechanical weathering processes. For both
chemical and mechanical weathering, it also serves to transport/erode the weathering product.
Ch 6 Exam Review
How does mechanical weathering aid chemical weathering?
ANSWER: Mechanical weathering produces smaller particles, with more surface area for the given
volume, and chemical weathering operates on the surface of the material.
How does mechanical weathering differ from chemical weathering?
ANSWER: In mechanical weathering physical forces break the rock materials into smaller pieces which retain
their chemical composition; in chemical weathering the composition is altered.
Name an important physical property about water that makes it unique among liquids.
ANSWER: It increases in volume when it freezes (changes from a liquid to a solid state).
Why is this unique property of water important in the physical weathering of rocks?
ANSWER: The expanding volume creates pressures which may break rocks and minerals into smaller pieces.
Global warming is predicted to occur from increased atmospheric carbon dioxide due to the burning of fossil fuels.
How might this increased level of carbon dioxide affect rates of weathering?
ANSWER: Increased amounts of atmospheric carbon dioxide should increase rates of weathering by carbonic
acid and hydrolysis if rainfall remains constant or increases.
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Ch 6 Exam Review