Transcript Chemical Weathering

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.
Water
Can cause rock to
be broken down
and dissolve.
Can take thousands
of years to take
place.
1. Water
• Dissolves minerals
from a rock over a
long period of time
(sometimes 1000s of
years).
2. Weak Acids
Include
1. acid precipitation
2. acids in ground
water
3. 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
Acids in
contains weak acids
Ground water
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 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 • Lichens produce
acids that slowly
things
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
3. Air
oxidation
• 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.
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?
•
•
•
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A. water
B. acids
C. wind
D. animals
Quick Check
Which of the following is a type of frost
action?
•
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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?
•
•
•
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A. lichens
B. acid precipitation
C. acids in groundwater
D. water
Quick Check
How do lichens slowly break down a rock?
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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?
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A. tennis ball
B. aluminum can
C. wooden fence
D. Bicycle tire