Physical and Chemical Processes Supported by Air: Air is a mixture of gases that forms an invisible layer of gaseous substance surrounding the Earth. There are different processes occurring all around us, and they may be physical as well as chemical processes. Before going into detail, we must have a clear picture of physical and chemical processes or changes. Physical change is the change in matter and other physical traits without any change in internal composition. At the same time, a chemical change is accompanied by a chemical reaction that changes the chemical composition of the original substance giving rise to a completely new substance. For example, melting of ice, evaporation, etc., are physical changes and burning of matchstick, cooking of food, rusting of iron rod, etc., are chemical changes. 

Now, we can observe numerous physical and chemical processes happening around us that are supported by air. The atmosphere is itself a blanket of air around the Earth that undergoes several physical processes like blowing of the wind, formation of clouds; the water cycle is a completely physical process where only the state of matter of water changes by evaporation, condensation, and precipitation. Similarly, many chemical processes are happening around us that is supported by air, such as combustion, corrosion, photosynthesis by plants, respiration in living beings, digestion, etc. All these chemical processes are irreversible and can occur only in the presence of oxygen gas that is one of the major constituents of air. 

Physical Processes Supported by Air

The Earth’s atmosphere is very dynamic, and many physical processes occur in the atmosphere due to certain changes. The causes of these physical changes are sometimes man-made and sometimes natural. Due to increasing air pollutants in the atmosphere, various changes are occurring, and scientists are continuously involved in the research of the causes of weather and climate change. These physical processes are not permanent and keep on changing. Some of the physical processes supported by air in the atmosphere are discussed below:

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1. Water Cycle – The natural water circulation in nature is called the water cycle. There are three major processes through which water is transported and released back into the atmosphere and vice versa, which are evaporation, condensation, and precipitation.

i. Evaporation is a phenomenon in which the liquid turns into a vapour state at a temperature below its boiling point.

ii. Condensation is the process in which the water vapour cools down to form tiny water droplets.

iii. The falling of large-sized water droplets on the Earth in the form of rain is also called precipitation.

2. Temperature change is a physical process that is a result of various factors in the air, including air pressure, wind, climate change, etc. The rate of evaporation also increases with an increase in temperature because as the temperature goes higher, the kinetic energy of the water molecules also increases and therefore, the rate of evaporation becomes faster.

3. Humidity change is another physical process that is the amount of moisture (water vapour) in the air.

4. Air Pressure change is a physical process in the atmosphere that is the force exerted by air molecules, whether it is compressed or unconfined, on the surface that encounters it.

5. The wind is a process of moving air caused by the difference in air pressure from one place to another.

6. Cloud formation is another physical process that is a result of condensation. As water vapours rise in the atmosphere, due to very low temperature, it changes into tiny droplets. These droplets come close together to form clouds in the atmosphere.

Chemical Processes Supported by Air

Chemical processes are mainly accompanied by chemical reactions that are mainly irreversible. In our surroundings, there are numerous chemical processes that are supported by air. Some of these are explained below:

Combustion – Combustion is a redox reaction that occurs between a fuel that acts as a reductant and oxygen gas present in the atmosphere as an oxidant that results in the formation of gases like carbon dioxide, water vapour and energy accompanied by flame and smoke. The chemical reaction involved in combustion is:

\({\rm{C}}{{\rm{H}}_{\rm{4}}}{\rm{ + 2}}{{\rm{O}}_{\rm{2}}} \to {\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O + }}\)Energy

Respiration – It is the biological oxidation of food or respiratory substrates inside the cells of the living organisms, using oxygen gas and producing carbon dioxide and water as by-products along with the release of energy in the form of ATP (adenosine triphosphate) that helps to perform metabolic activities inside our body. 

Cellular Respiration \(\Rightarrow {{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}{\rm{ + 6}}{{\rm{O}}_{\rm{2}}} \to {\rm{6C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 6}}{{\rm{H}}_{\rm{2}}}{\rm{O + ATP}}\)

Rusting – Rusting of iron refers to the formation of rust, which is a mixture of iron oxides, on the surface of iron objects. Rust is formed by a redox reaction between atmospheric oxygen and iron in an environment containing water. It is an irreversible process.

Photosynthesis is the most common example of a photochemical reaction that is supported by \({\rm{C}}{{\rm{O}}_{\rm{2}}}\) in the air. In this process, plants prepare their food by using sunlight and water to convert carbon dioxide into glucose and oxygen.

Atmosphere and Air Pressure

The atmosphere is a layer of gases that envelope the Earth and is held by the gravity of the planetary body. It helps all living organisms to survive and maintains the temperature of the Earth, and protects us from harmful UV radiations coming from the sun. 

The chemical composition of air in the atmosphere is shown below:

Air Pressure – The pressure exerted by the air around us is known as the air pressure, while the atmospheric pressure is the pressure exerted by the atmosphere on the Earth. Air pressure is measured by tire gauge; on the other hand, atmospheric pressure is measured using a mercury barometer. 

Summary

Air is a mixture of invisible gases that supports life on the Earth. There are many types of changes or processes occurring in the atmosphere continuously. Based on certain characteristics, these changes or processes are classified as physical and chemical changes or processes. The change in which the molecular composition is completely changed and a completely new product is formed is called a chemical change. These changes are generally irreversible and permanent. A chemical change is accompanied by the energy change as the breaking of old bonds in reactants, and the formation of new bonds in products takes place.

The chemical reactions in which energy is released is known as exothermic reaction, and the chemical reactions in which energy is absorbed is known as endothermic reaction. For example, combustion, respiration, photosynthesis in plants, corrosion, etc., are examples of chemical processes supported by air. Conversely, in a physical change, only the arrangement of molecules is altered, leading to change in its state and no new products are formed. Such changes are reversible and temporary; for example, water onzing forms ice and ice on melting again forms water. In the atmosphere, many physical processes occur that are supported by air, like blowing of the wind, air pressure, water cycle, humidity, temperature changes, etc. Thus, the air is a very important and vital constituent of our life.

FAQs on Physical and Chemical Processes Supported by Air

Q.1. What is the chemical reaction of air?
Ans: In the air, a chemical reaction known as combustion takes place. It is a redox reaction that occurs between a fuel and oxygen gas present in the atmosphere that results in the formation of gases like carbon dioxide, water vapour and energy accompanied by flame and smoke. The chemical reaction involved in combustion is:
\({\rm{C}}{{\rm{H}}_{\rm{4}}}{\rm{ + 2}}{{\rm{O}}_{\rm{2}}} \to {\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\) Energy

Q.2. What are the physical changes/processes occurring in the atmosphere?
Ans: The physical changes in the atmosphere are the water cycle that is the natural water circulation in nature. There are three major processes through which water is transported and released back into the atmosphere and vice versa, which are evaporation, condensation, and precipitation. Temperature change is a physical process that is a result of various factors in the air, including air pressure, wind, climate change, etc. Humidity change is another physical process that is the amount of moisture in the air. Air pressure change is a physical process in the atmosphere that is the force exerted by air molecules, whether it is compressed or unconfined, on the surface that encounters it. The blowing of wind is a process of moving air caused by the difference in air pressure from one place to another. Cloud formation is another physical process that is a result of condensation. As water vapours rise in the atmosphere, due to very low temperature, it changes into tiny droplets. These droplets come close together to form clouds in the atmosphere.

Q.3. Can sea salt affect the chemistry of the atmosphere?
Ans: Sea salt can affect the chemistry of the atmosphere to some extent as the salt particles may release halogens into the atmosphere. They undergo chemical reactions that affect the amount of ozone and methane in the atmosphere, which may further impact temperatures. Thus, affecting the chemical constituents of the atmosphere.

Q.4. What is the composition of the atmosphere made of?
Ans: The chemical composition of the atmosphere is composed of nitrogen \(\left( {78.1\% } \right)\), oxygen \(\left( {2.9\% } \right)\), argon \(\left( {0.93\% } \right)\), carbon dioxide \(\left( {0.04\% } \right)\), trace amount of other gases and water vapour (variable), along with ammonia, methane, hydrogen, etc

Q.5. What is a particle of salt called?
Ans: Salt particle is a grain-like particle that is mainly composed of sodium chloride \(\left( {{\rm{Nacl}}} \right)\) crystals and other halides of alkali metals and alkaline earth metals. They exist as ionic compounds. The size of sea salt particles ranges from \(0.05\) to \({\rm{10\mu m}}\) in diameter.

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