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A chemical change occurs when one material is transformed into a new material by the synthesis or decomposition of substances. These types of changes are usually irreversible. Any change occurring in the matter can be of two types: physical change or chemical change.
- It occurs when two or more substances combine, which is also called a chemical reaction.
- A chemical reaction is defined as an arrangement of atoms of the reactants to create different substances as products.
- When heat is generated in these reactions, they are called exothermic reactions.
- Endothermic reactions are types of reactions in which the reactants absorb heat from the surroundings to form products.
- Cooking up food, baking cakes and cookies, and digestion of food are some common examples of chemical change.
Key Terms: Chemical Change, Chemical Reaction, Matter, Endothermic reaction, Exothermic reaction, Physical Change, Energy, Substances, Reactants, Organic Compounds, Inorganic Compounds, Biochemical Changes
What is a Chemical Change?
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Chemical change occurs when a substance combines with another to form a new substance and results in a change in the composition of a substance. The change is caused by oxidation and reduction reactions.
- The building and breaking of bonds are two components of chemical change.
- These changes are irreversible, barring any other chemical reactions.
- The bonds between atoms are broken during a change, and new bonds are formed to create the required product.
- The process involves the exchange or transformation of energy.
- It is used in the fields of chemistry, biology, and environmental science.
Chemical change explains the transformation and behaviour of matter, the synthesis of new compounds, and the impact of chemical reactions on the environment and everyday life.
Examples of Chemical Change in Everyday LifeExample: Look at the below examples of chemical change. A lot of which can be seen in everyday life.
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Chemical Change
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Properties of Chemical Change
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Chemical properties describe the ability of a substance to undergo a certain chemical change. Here are the properties of chemical changes:
- Chemical changes are irreversible, which means that after a chemical reaction, it cannot be reversed to return to the initial substances.
- The molecular composition of products differs from the molecular composition of reactants.
- The chemical configuration of substances changes during a chemical reaction.
- One or more new chemical substances, i.e. products, are produced when two or more reactants react in a chemical reaction.
- As reactants react to form new compounds by breaking down or merging, there is a temperature change.
- So, during a chemical reaction, either energy is absorbed or released.
When energy is absorbed during a chemical change, it is called an endothermic reaction, and when energy is released, it is called an exothermic reaction.
Signs of Chemical Change
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The below-listed characteristics will help you identify if a chemical change has occurred.
Temperature Change
Temperature change is quite common in chemical change. The temperature can be measured by inserting a thermometer inside a vessel. If it rises, that means chemical change is taking place.
Colour Change
Change in the colour of an object is another characteristic of chemical change. It can be explained with the help of rusting of an iron.
Odour
When more than one type of element is mixed together in a chemical reaction, then an individual can experience an odour or scent, which indicates the occurrence of chemical change.
Precipitate Formation
The formation of precipitation is another sign of chemical change that takes place in a chemical reaction. It occurs when a solid is formed within another solid or solution.
- This process is known as precipitation.
- The most common example is the carbonate reaction with barium.
Bubble Formation
Bubble formation is an indicator of chemical change. The formation of bubbles is also accompanied by a change in temperature. The most common example is the reaction of sodium carbonate with hydrochloric acid.
Chemical Changes with Organic Compounds
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Organic compounds contain one or more carbon atoms covalently bonded with each other or with elements of other atoms. A few examples of chemical changes involving organic compounds are stated below:
Ripening and Rotting of FruitsWhen fruits ripen, their chemical composition changes. This change is irreversible. Now, a chemical change also occurs when fruits rot, which is again an irreversible change. Burning of Natural GasNatural gas comprises methane gas, which reacts with oxygen from the atmosphere and forms carbon dioxide and water. It is a combustion reaction.
Burning of Natural Gas |
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| Difference Between Acid and Base | Bomb Calorimeter | Solvent Examples |
| Oxygen Cycle | Examples of Weak Acids | Weak Base |
Chemical Changes with Inorganic Compounds
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Substances in which two or more elements (usually except carbon) are combined to form compounds are called inorganic compounds. A few examples of chemical changes involving inorganic compounds are stated below:
Rusting of IronRusting of iron occurs due to an oxidation reaction. When iron comes into contact with water or oxygen, rusting occurs. It is a form of inorganic corrosion.  Rusting of Iron Acid-base TitrationIn titration reactions, acid and base react with each other to form salt and water. Usually, an indicator, which is known by a change in colour, is used to determine the completion of the reaction.
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Biochemical Changes
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Chemical changes occurring in living organisms involving complex processes for their growth and activity are biochemical changes. Some examples of biochemical changes include:
Photosynthesis
Photosynthesis is a process by which plants convert carbon dioxide and water into sugar and oxygen.
Digestion of food
The process of digestion of food enhances growth in organisms. The enzymes break down food particles into smaller, digestible particles resulting in a chemical change.
Things to Remember
- Chemical change, also known as chemical reaction, is irreversible and permanent.
- It changes the chemical configuration of the substance by forming new chemicals.
- Signs of a chemical change include changes in colour, temperature, density, formation of gas, formation of precipitates, and production of light.
- In physical change, the molecular arrangement of molecules is changed.
- Redox reactions and displacement reactions are common examples of chemical changes involving inorganic compounds.
Sample Questions
Ques. How do you identify a chemical change? (2 marks)
Ans. Chemical changes have some characteristics that can help you identify them, like changes in temperature, color, odor, density, or taste, production of light, formation of gas, and formation of a precipitate.
Ques. Give some examples of chemical change in everyday life? (2 marks)
Ans. Plant growth, formation of cheese from milk, burning candles, lighting a match stick, fireworks exploding, rusting of iron, burning of gas on a kitchen stove, baking of biscuits, cooking food, digestion of food are some of the many examples of chemical change in everyday life.
Ques. What is a chemical change? (2 marks)
Ans. A chemical change is also known as a chemical reaction. When two or more substances react with each other and form new products, a chemical change is said to have occurred. The chemical configuration of these reactants and products is different. Generally, chemical changes are permanent and irreversible.
Ques. Why do we call the burning of paper as chemical change? (3 marks)
Ans. When wood or paper is burnt in the air, it gives carbon dioxide and water leaving behind a little ash.
We call it chemical change because-
(i) In the above reaction new substances are formed. Impurities that are non-volatile remain behind.
(ii) The change is permanent.
(iii) Heat and light energies are given out.
(iii) Mass of wood gets changed but the total mass remains the same.
Ques. Give an example of each of the following chemical changes? (4 marks)
(a) A reaction involving
(i) Change of state
(ii) Formation of a precipitate
(b) An exothermic and endothermic reaction involving carbon as one of the reactants.
(c) A reaction where the color change is noticed.
Ans. a) The reaction are as follows:
i) C(s)+ 2S → CS2(l)
ii) FeSO4(aq) + 2NaOH(aq) 
FeOH2 ↓+Na2SO4 (aq)
- Exothermic reaction: When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced.
C + O2 → CO2 + Heat
Endothermic reaction: When carbon is heated with sulfur at a high temperature, liquid carbon disulfide is formed.
C + 2S →Δ CS2
c) 
Ques. Differentiate between physical and chemical changes? (4 marks)
Ans. The difference between physical and chemical changes are as follows:
| Physical Changes | Chemical Changes |
|---|---|
| The changes that occur in the physical state of matter, such as the change in shape, size, or state, are physical changes. | The changes that occur in the chemical configuration of substances which can be known by the change in temperature, color, etc. are chemical changes. |
| These changes are mostly temporary and reversible. | Generally, these changes are permanent and irreversible. |
| No new products are being formed. | New products are formed. |
| Example: ice to water | Example: the formation of curd from milk |
Ques. Which of the following are chemical changes? (5 marks)
(A) Growth of a plant
(B) rusting of iron
(C) Mixing of iron filings and sand
(D) Cooking of food
(E) Digestion of food
(F) Freezing of water
(G) Burning of a candle
Ans. A. Growth of a plant- It is an irreversible change. It is found that photosynthesis is a chemical change process that involves the formation of new products. Hence, we can say that it is a chemical process.
- Rusting of iron- It is an irreversible process, that involves the formation of new products. Hence, we can say that it is a chemical process.
- Mixing of iron filings and sand- It is a reversible process, as by using a magnet these can be easily separated.
- Cooking of food- It is an irreversible process, where some reactions take place that forms a different product. Hence, we can say that it is a chemical process.
- Digestion of food- we can say that it is a chemical change, as digestion of food produces different reactants.
- Freezing of water- It is a reversible process, as it is a physical change. For example, ice can be melted to get water.
- burning of a candle- we can say that it is a chemical change, as it is found that wax is made up of hydrocarbons that melts and becomes a gas. It is also found that the hydrocarbons are broken.
So the correct answer is “A, B, D, and G”.
Ques. What changes are visible after ripening of fruits? (3 marks)
Ans. The changes that are visible after ripening of fruits are as follows:
- The most common change is that fruit, after ripening, becomes juicy and soft.
- Since there is a breakdown of chlorophyll, the colour of the skin of the fruit changes.
- The aroma of the ripe fruit changes.
Ques. What is esterification? (2 marks)
Ans. Esterfication involves a reaction between organic acid and alcohol. The process of esterification involves a combination of compounds to produce ester and water. It is most commonly used in the production of fragrances, flavours, and plasticizers. The most common example of esterification includes a reaction between acetic acid (CH3COOH) and ethanol (CH3CH2OH) to form ethyl acetate (CH3COOCH2CH3).
Ques. What type of chemical change takes place in the formation of steel? (2 marks)
Ans. The formation of steel is an irreversible process. In this process, steel is formed by the addition of different types of elements in required quantities, with carbon as the basic element. The process results in the formation of new substances, which is considered a type of chemical change. The properties of required substances are different from those of iron.
Ques. What is law of conservation of mass? (2 marks)
Ans. The law of conservation of mass states that mass placed in a closed system is neither created nor destroyed but can be transformed from one form to another. In this, the mass of reactants is equal to the mass of products. It was discovered by Antoine Laurent Lavoisier in 1789.
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