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Chemical Equations

We are from a chemical reaction! We are from a chemical reaction! Life is a series of chemical reactions (metabolic), but from where the life is originated? Scientific hypotheses about the origin of life may be divided into several categories. Most widely accepted phenomenon is, Abiogenesis. Yes, life is originated from a series of chemical reactions from inorganic matter. Scientists demonstrated that aminoacids, the building blocks of life were synthesized in primordial fluid (the primitive oceans of the Earth) from inorganic chemicals such as NH3, H2S, CO2 etc. From these aminoacids, the self replicable nucleic acids (RNA and DNA) were synthesized from which the beginning of life had started.

Learning Objectives

After completing the topic, the student will be able to:

  • Differentiate chemical and physical reactions (changes).
  • Write the chemical formula of a given compound and memorize the chemical formula of different compounds.
  • Write chemical equations with standard notations.
  • Balance the chemical equations by following different methods such as trial and error method, ion–electron method etc.
  • Classify different types of reactions.
  • Identify the process involved in a given reaction.
  • Characterize the type of reaction by observing changes such as evolution of gas and formation of precipitate etc.
Chemical Changes Life is a series of chemical changes
Rust on Iron nails
Chemicals are omnipresent

Chemicals are everywhere, all the substances in the world are chemicals. The rocks, the plants, the animals, all are made up of chemicals. Look around yourself. Ripening of a fruit, the changing of milk into curd, the digestion of food in our body, rusting of iron objects on exposure to damp air, growth of a child are some of the examples of chemical reactions.

When wood burns, heat is released. The end product is ash. This happens because the chemicals in the wood change on heating. The chemicals in the wood change into something different (ash) from wood.

The air we breathe is a mixture of gases such as oxygen, nitrogen, carbon dioxide and water vapor. These are chemicals. When food is digested in the stomach, the chemicals in the food undergo a series of reactions, to give us energy to live.

The water we drink, the food we eat, the clothes we wear, the buildings we live in, all are chemicals. Almost 65% of our body is water, the rest is made up of complex molecules such as proteins and lipids. They are also chemicals.

Plants are also made up of chemicals. In fact they are capable of mixing all the natural chemicals for their needs and they also make many new chemicals that we need. From plants we get food, medicines, fibers, fuel and many other useful chemicals.

When plants and animals die and get buried, over million years, their chemicals change to give us fossil fuels like petrol, diesel and gas. These changes are chemical reactions again!

Physical and Chemical changes Examples for physical and chemical change
Physical and chemical changes

When an ice cream melts, what do you think is happening? The cold ice cream changes physically from a solid to a liquid form. It is a physical change. When salt or sugar is dissolved in water, it is a physical change, too. On the other hand when a candle is burning, the melting wax is a physical change but the heat and light that we get is due to chemical changes or reaction of the wax molecules with oxygen molecules in the air. This is a chemical change.

When a light bulb is emitting light by electricity – is it a physical change or a chemical change? When switch is ON, the tungsten filament is heated up by an electrical current (or electrical energy). It becomes red hot and produces light. When switched OFF, the filament cools to regain its original form. There is no chemical change in the bulb. When a firecracker is lighted – is it a physical change? No, surely not. The chemicals in the firecracker burn to give bright colored sparks and flashes. These are chemical changes.

In all the above examples, wherever there is a chemical change, a common thing is happening to the chemicals. The chemicals are combining to give new chemicals. What does it mean in terms of chemical bonds, at a tiny microscopic level of atoms and molecules? Well, the chemical bonds break and new bonds are formed in the new chemicals. Thus we can say that a chemical change is a permanent change or irreversible change. In this change the original substance gives rise to one or more substances with different properties. The original substance cannot be obtained easily again.

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