Physical and Chemical Changes – Physical Change, Chemical Change, Their Differences, Practice Problems and FAQ

This concept page deals with the physical and chemical changes. To better understand, consider an iron rod.

What happens when the iron rod is bent?

It undergoes a physical change. The iron rod which was linear before has lost its linearity.

Similarly, what happens when the iron rod gets rusted?

The iron atoms in the iron rod are oxidised to iron oxide. Therefore, it undergoes a chemical change.

In this concept page, we will get to know more about physical changes, chemical changes and their differences.

TABLE OF CONTENTS

• Physical Change
• Chemical Change
• Difference between Physical and Chemical Changes
• Practice Problems
• Frequently Asked Questions – FAQ

Physical Change

A substance's structure and chemical makeup are both impacted by these modifications. Because the modifications it makes are reversible, the situation can return to how it was originally. When a substance undergoes modifications that do not influence its chemical bonds, a physical change takes place. It results in modifications to a substance's external appearance, including changes to shape, colour, and size. It is used to separate mixtures into the substance's constituents. These modifications are made through reactions that do not alter the chemical structure in any way. It is contrary to a chemical change, where the reactants combine to create new products. In order to separate mixtures into their respective components, physical modifications are used. It is employed to separate a chemical into more basic components. It also involves modifications to its specific physical characteristics, such as texture, toughness, and change.

Heating and cooling: A substance’s phase can be changed by either heating or cooling it. When a substance is heated, it changes its physical state from a solid to liquid or liquid to gas or solid to gas. When a substance is cooled, it changes its physical state from gas to liquid or liquid to solid, or gas to solid.

Magnetism: Materials that naturally exhibit ferromagnetism are magnetic. It is reversible.

Example: Melting of ice. A block of ice can turn into liquid water as the temperature changes, but the water can also turn back into ice on cooling.

Chemical Change

Chemical changes usually happen when two or more substances combine and this combination results in a change in their chemical bonds. Chemical changes are permanent. They are unable to return to their former configuration after they have changed into a different form. Chemical changes are also referred to as chemical reactions. The rearrangement of the atoms that occurs during chemical changes typically results in the gain or loss of electrons. Exothermic and Endothermic reactions are thus two categories of chemical reactions. Exothermic chemical changes are those in which heat energy is released to create a new product. Heat and light are the two forms of energy that are released. An endothermic chemical change is another type of chemical change in which energy is required for a reaction to take place. There are numerous further types of chemical changes.

Organic Change - Organic change is the chemical change occurring in a compound containing carbon.

Biochemical Change - This change relates to chemical processes that take place throughout the function and development of biological things.

Example: Rusting of iron is a well-known example of chemical change. Iron forms ferric oxide when it is exposed to air and oxygen (Fe2O3). The iron acquires a reddish-brown hue as a result.

Difference between Physical and Chemical Changes

Practice Problems

1. Which of the following properties remain constant during both chemical and physical changes?

1. Particle arrangement
2. Particle size and shape
3. Density
4. Mass

Answer: D

Solution: Chemical and physical changes adhere to the law of mass conservation. As a result, mass remains constant. The properties given in other options can change in physical and chemical changes.

So, option D is the correct answer.

2. Which of the following is an example of physical change?

1. Sublimation of dry ice
2. Buring of wood
3. Preparation of caramel by heating sugar
4. Corrosion of a metal

Answer: A

Solution:

1. The sublimation of dry ice is a physical change in which solid carbon dioxide undergoes a phase change into a gaseous state.

2. Burning of wood results in the formation of new products. Therefore, it is a chemical change.

3. Heating of sugar to prepare caramel is a chemical change as the oxygen in the air reacts with sugar and chemical bonds are broken.

4. Corrosion of a metal is a chemical change because metals react with gases like oxygen in the air to form new products.

Thus, the process given in option A is a physical change.

So, option A is the correct answer.

3. Which of the following are examples of physical or chemical changes?

1. petrol exhaustion
2. LPG combustion
3. Milk curdling
4. condensation of steam

1. a) and b) are physical changes, c) and d) are chemical changes
2. a) and b) are chemical changes, c) and d) are physical changes
3. a), b) and c) are physical changes, d) is a chemical change
4. a), b) and c) are chemical changes, d) is a physical change

Answer: D

Solution:

1. Exhaustion of petrol is a chemical change as the chemical composition of petrol changes on exhaustion.

2. Combustion of LPG is also a chemical change as new products are formed on combustion.

3. Curdling of milk is an irreversible process in which the curd formed cannot be reverted back into milk. Therefore, it is a chemical change.

4. The condensation of steam is a physical process in which steam (gas) undergoes phase change into liquid water. The liquid formed by the condensation of steam can be converted back to steam by heating. Thus, it is a reversible process.

Thus, the processes given in a), b) and c) are chemical changes whereas, the process given in d) is a physical change.

So, option D is the correct answer.

4. Which of the following statements truly represent the nature of chemical change?

1. It occurs when several substances combine, causing their chemical bonds to change.
2. The chemical changes are permanent.
3. They are unable to return to their original shape once they have changed.
4. All of these

Answer: D

Solution:

1. Chemical changes occur when two or more substances combine, leading to the change in the chemical bonds.

2. Chemical changes are generally irreversible. The products once formed cannot be reverted back into the reactants.

3. A substance undergoing a chemical change can not retain its original shape once the chemical change has occurred. Chemical changes are also referred to as chemical reactions.

Thus, the statements given in options A), B) and C) are true.

So, option D is the correct answer.

Frequently Asked Questions – FAQ

1. How do you distinguish between physical and chemical changes?
Answer: During a physical change, the appearance or form of matter changes, but the type of matter in the substance does not. A chemical change, on the other hand, produces at least one new substance with new properties.

2. Why is it important to understand the distinction between physical and chemical changes?
Answer: It is critical to distinguish between chemical and physical changes. There are several obvious changes, but there are some fundamental concepts to be aware of. Physical changes are typically changes in the physical state of something. Chemical changes occur on a molecular level when two or more molecules interact.

3. What are the three physical forces that can cause a change?
Answer: Physical changes can be caused by three major forces such as motion, temperature, and pressure. On the contrary, chemical changes can be caused by the combination of two or more substances in addition to motion, temperature and pressure.

4. Can physical and chemical changes happen simultaneously?
Answer: Yes, physical and chemical changes can happen simultaneously in some cases. The burning of a candle is one such example. The wax in the candle melts and becomes liquid. This implies that the change is physical in nature. At the same time, the carbon and hydrogen in the candle react with the oxygen in the air to form new products. This implies that a chemical change is taking place.

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