Geography is the study of places and the relationships between people and their environments

1. -RASHMI SAMMI
(PGT GEOGRAPHY)
K.V. A.G.C.R. COLONY DELHI

2. OBJECTIVES:
•To make students understand the concept of Chemical weathering.
•To make students know about different types of Chemical weathering.
•To make students aware about the process of Chemical weathering.

3. TEACHING AIDS :
POWER POINT PRESENTATION WITH VARIOUS PICTURES AND
DIAGRAMS,
GOOGLE MEET WITH THE HELP OF LAPTOP,CLEAR
GLASSES,WATER VINEGAR AND CHALK.
TEACHING METHODOLOGY
•Question Answer method
• Lecture method
• Audio Visual Method and use of ICT
•Demonstration Method

4. PREVIOUS KNOWLEDGE
Q1. What is Weathering?
Q2. What are the different types of weathering?
Q3. ‘Weathering is one of the denudation process’, True or False.

5. CONTENT
CHEMICAL WEATHERING
Introduction
Process
Types of chemical weathering
o Solution
o Hydration
o Oxidation
o Carbonation

6. Introduction
Weathering is an important
geological mechanism which
can destabilize the earth’s surface materials
and remove them by erosive processes.
Weathering is the physical disintegration
and chemical decomposition of a rock mass
on the land.
Weathering is a collective term used to
denote the mechanical, chemical and
biological(organic) processes that take
place on the earth’s surface.

7. Chemical
weathering
Chemical and structural characteristics of minerals
present in rocks are also expected to play a significant
role in weathering
Chemical weathering changes the composition of
rocks, often transforming them when water interacts
with their minerals to create various chemical
reactions.
Tightness of packing of ions in crystals
Ferro magnesium minerals are more susceptible to
chemical weathering than feldspar and quartz.

8. Chemical weathering processes
 It is the process of decomposition of Earth’s surface
materials.
 It is done by various agents and chemical reaction. The
reactions, here, are exothermic and result in the increase
in volume of minerals that contribute to the physical
disruption of rock.

9. Rate of chemical weathering
The rate of Chemical weathering depends on various factors
like
 Temperature
 Amount of surface area and
 Availability of water or natural acid.

10. Processes of chemical weathering
The major processes involved in chemical
weathering are:
 Solution
 Oxidation
 Hydration
 Carbonation

11. Solution
 Solution is the process of dissolving mineral constituents by
water or acid.
 Most minerals have low solubility in pure water, but rain
contains carbonic acid, so that carbonate minerals dissolve
readily in acidic solutions.
 Some substances present in the rocks are directly soluble in
water.
 .

13. HYDRATION
*Hydration involves absorption of water.
*Chemical combination of water molecules with a particular
substance or mineral leading to a change in structure.
*Soil forming minerals in rocks do not contain any water and
they undergo hydration when exposed to humid conditions.

16. Oxidation Atmosphere contains 21% of free oxygen. Whereas the
oxygen content of air dissolved in water is 30- 35%.
These two forms of oxygen are the most active
chemical agents for weathering.
Oxidation of Minerals and Rocks is an effective
process in decoloration and decomposition of
materials.
In this process, the atmospheric oxygen combines
with the metal ions of minerals to form oxides (or
hydroxides).
Sulphide minerals become unstable & gradually
substituted by sulphates

17. Carbonation and Dissolution
1. Carbonation is the reaction of carbonate or carbonate ions with minerals.
As rainwater falls through the atmosphere it dissolves small amounts of
carbon dioxide.
2. The atmospheric carbon dioxide when dissolved in water it forms
carbonic acid.
3. Carbonic acid plays a significant role in chemical weathering. Carbonic
acid is formed naturally in rainwater. Additional carbon di oxide is picked-
up in the ground from decaying vegetation.
4. Carbonic acid is the principal weak acid- responsible for Chemical
weathering.
5. Acidic rainwater is also very effective at breaking down calcium
carbonate.

18. Recapitulation
1. The process that breaks down rocks and other materials on Earth's surface is called
a)Weathering
b) Erosion
c) Deposition
d) none of above
2. Rust that forms on rocks or metal because of extended exposure to oxygen is what
example of chemical weathering?
Carbonation
Oxidation
Hydration
None of the above

19. 3. Caves being formed by acid rain dissolving underground
limestone due to __________ .
a)Weathering
b) Erosion
c) Deposition
d) none of above

20. ASSIGNMENT:
 Define chemical weathering?
 Explain different types of Chemical weathering.

21. THANKYOU