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What is a Chemical Change

Chemistry is a branch of science that deals with the study of chemicals as one of the main concepts. The elaborated description of chemical changes has become the primary goal of science in today's world. The study of chemicals and their interaction has played a significant role in discovering many new phenomena. The transformation of one substance into another form of the substance is known as a change, and a substance's ability to undergo a specific change in its chemical properties is known as chemical change. Chemical changes are also called chemical reactions. In a chemical reaction, one or more substances are changed into one or more new substances.

For example, zinc is silver-grey naturally. At room temperature, when zinc is reacted with bright yellow-colored sulfur by providing some heat, a white-colored product known as zinc sulfate is obtained, as shown in the below image. Therefore, a chemical reaction leads to a chemical change.

1. Zinc

What is a Chemical Change

2. Sulfur

What is a Chemical Change

3. Zinc Sulphate

What is a Chemical Change

A famous scientist named Antoine Lavoisier has precisely defined changes as:"Nothing is lost, nothing is created, everything is transformed."

In general chemistry, there are two types of changes-

  1. Chemical changes: Changes involving the rearrangement of atoms to form one or more different substances are defined as chemical changes. The chemical properties of products are entirely different from reactants.
  2. Physical changes: Changes that occur when there is an alteration in the physical properties of a substance. Physical changes do not affect the chemical identity of a substance. They only bring changes in the state of a substance.
What is a Chemical Change

Properties of Chemical Changes:

A chemical change can be distinguished from a physical change based on its properties. Following are some properties or evidence of a chemical change

  1. Irreversibility: Changes due to chemical reactions cannot be converted back to their original form, i.e., they cannot be reversed. This property of a chemical change is a very significant difference when compared with a physical change. Therefore, chemical changes are called permanent changes or irreversible changes. For example, cooking of raw eggs, increase in height, burning of paper, formation of curd from milk, breaking of glass, etc.
  2. Formation of new substances: During a chemical change formation of two or more new substances always occurs. These new substances possess properties that are different from the original substance.
  3. Production of light or heat: Many chemical reactions give off heat and light during a chemical change. Reactions in which heat is released are called exothermic reactions. A temperature increase also accompanies the release of heat. For example, combustion of candle. This chemical reaction gives off both light and heat. Similar to this is the combustion of wood and propane in gas stoves.
    What is a Chemical Change
  4. Colour change: Rotten food is an example of chemical change under the colour change property. The image shown shows how, after a chemical reaction, the colour of the apple changes from green to brown. Another example is rusting of iron.
    What is a Chemical Change
  5. Odour (smell) Development: When food reaches its expiry date, it undergoes some chemical reactions with its surrounding environment, which lead to the formation of new substances that have their unique smell, which is often unpleasant to smell.
  6. Change of Composition: Change in composition is another evidence of chemical change. For example, paper turns into ash.

Types of Chemical Changes:

The above evidence or properties of chemical changes are further categorized into three types of chemical changes:

  1. Inorganic Changes: Changes between elements and compounds not involving carbon are known as inorganic changes. For example, neutralization reaction and oxidisation involving rusting of iron.
  2. Organic Changes: Organic chemistry is the study of carbon-containing compounds. Organic chemical changes are the changes wherein carbon atoms react with and other elements or compounds. Polymerisation, hydrogenation, oil refinery, condensations, addition, elimination, substitution, etc., are the reactions studied under organic changes.
  3. Biochemical Changes: The chemistry of living organisms is known as biochemistry. It deals with the chemical changes in living organisms. It is more like biology. This is one reason behind the complexity of explaining and understanding biochemistry. Changes observed during photosynthesis, protein synthesis, and food digestion are biochemical changes.
    What is a Chemical Change

These three terms are the pillar of chemical changes. Anything studied under chemical changes is directly or indirectly connected to these three changes, their applications, properties, and mechanisms. Every chemical change occurs only under suitable environmental conditions.

Characteristics of Chemical Change:

1) Evolution of Gas:

Some chemical changes involve the evolution of gas while the reaction proceeds.

The evolution of hydrogen gas characterizes a chemical reaction between zinc and sulphuric acid.

Zn + H2SO4 -----> ZnSO4 +H2

Similarly, the reaction between zinc and hydrochloric acid is characterized by bubbles of hydrogen gas near the mouth of the flask.

Zn + 2HCl -----> ZnCl2 + H2

2) Formation of Precipitation:

Precipitation is an insoluble solid formed in a chemical reaction. The chemical reaction between copper sulfate and sodium hydroxide produces blue precipitation of copper hydroxide.

CuSO4 + 2NaOH -> Na2SO4 + Cu (OH) 2

(Blue ppt)

3) State Change:

All matter exists in three forms/states: solid, liquid, and gas. An example of a state change reaction is the combustion of candle wax.

C2H5 + O2 ->CO2 + H2O + Heat and light

Difference between Chemical Change and Physical Change:

Physical Changes Chemical Changes
In a physical change, there is no formation of new substances and products. In a chemical change new substance or product is formed.
They are temporary/ reversible changes. They are permanent/ irreversible changes.
Physical changes do not affect the chemical bond. During a chemical change, existing bond break, and new bonds are formed.
Since physical changes are reversible changes, the substance identity is retained in this process. Substance identity is not retained.
In physical changes, the composition of matter does not change. Composition of matter changes.
They bring change in the physical properties. They bring change in the chemical property of substances.
Crumbing of paper. Melting of ice. Crushing of plastic bottle. Evaporation of water. The casting of silver in mould. Maxing of sand and water. Maxing of marbles. Mixing of oil and water.
Burning wood. Souring of milk. Cooking of egg. Baking of cake. Rusting of iron. Cutting of tree Breaking of glass.

Chemical Changes from Everyday Life:

1) Photosynthesis:

Photosynthesis is a chemical reaction to convert carbon dioxide and water into glucose (food) and oxygen. Oxygen gas is evolved in this reaction, and an energy source compound called glucose is obtained. This chemical reaction takes place in the presence of sunlight. This is one of the most essential chemical reactions because it helps plants make food and provide oxygen to animals.

6CO2 + 6H2O + Sunlight -> C6H12O6 + 6O2

2) Aerobic Cellular Respiration:

Unlike photosynthesis in aerobic cellular respiration, glucose molecules combine with oxygen molecules to release carbon dioxide and water molecules. The Equation for aerobic salary respiration is-

C6H12O6 + 6O2 ->6CO2 + H2O + Energy

The energy release is in the form of ATP. Generally, 37 Adenosine triphosphate molecules are released in one cycle of aerobic cellular respiration.

3) Metathesis:

Metathesis is a chemical reaction between vinegar and baking soda to produce carbon dioxide and water bubbles of carbon dioxide gas are produced during the chemical reaction. It is a multi-step reaction usually performed while baking.

4) Soap and Detergent Reaction:

Cleaning Agent soap and detergent clean through a chemical reaction.

5) Electrochemistry:

The conversion of chemical energy into electrical energy is known as electrochemistry. Batteries use electrochemistry or redox (reduction Oxidation) reactions to convert chemical energy into electrical energy.

6) Anaerobic respiration:

Anaerobic respiration is the process of Adenosine triphosphate synthesis by the cells in the absence of oxygen example, anaerobic respiration by yeast and bacteria to produce alcohol.

Sometimes it is difficult to determine whether a change is chemical or physical. For example, when two or more metals are mixed to form an alloy, the properties of an alloy are entirely different from the metal it is formed for. Like brass, a standard alloy is made of copper (60%) and Zinc (40%), but brass properties neither match copper nor Zinc. Even though the properties of alloys (brass) differ from their constituent metal (copper and Zinc), it is not a chemical change because alloy and metal are not chemically bonded. As a result, brass represents physical change.


Every event essential to life in the universe is because of chemical changes; it is because of the chemical reaction that human beings reproduce, grow, heal, digest, etc. The reason behind the growth of plants and the colour of fruits and flowers are all because of chemical reactions. Chemical changes are not only chemical reactions but also biological processes. The heart pumping and our ability to think are all chemical processes in the body. Chemical changes correlate chemistry to the biology of humans. Inorganic and organic changes deal mainly with reactions, whereas biochemical changes deal with biological processes. Hence, a particular set of conditions is required for a chemical change to occur.

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