Physical and Chemical Changes: Overview, Differences, Experiments

Change does not happen by itself. A cause always accompanies a change in a substance. Ice, for example, does not melt to generate water on its own. Ice must be heated to melt and turn into water. Change is divided into two types namely, physical and chemical changes.

A physical change is a temporary and simply reversible change in which the physical properties of a substance change. A chemical change is a permanent change in which the chemical composition of a substance is changed. In this article, we have provided detailed information on physical and chemical changes. Scroll down to continue more!

Types of Changes: Overview

There are two types of changes as listed below:

1. Physical Change
2. Chemical Change

Physical Changes

A physical change is a temporary and easily reversible change in which the physical properties (e.g., physical state, shape, size, appearance, density etc.) of a substance change. Some physical changes are: glowing of an electric bulb, sublimation of iodine, melting of wax, melting of sulphur, evaporation of water and other liquids, formation of dew, crystallization of salt,zing of liquids, drying of wet clothes, bending of a glass tube, etc.

1. Change of State

Change of state (or form) in water is a physical change. On heating, ice melts, and water evaporates. On cooling, the water vapour cools to form water and waterzes to form ice. This is a reversible change where the form of water changes on reversing the conditions. Melting of wax and butter is the change of state.

2. Making Mixtures is a Physical Change

We mix iron filings with powdered sulphur; it forms a mixture from which iron filings can be separated from sulphur.

In all physical changes, the change is temporary and reversible. No new substance is formed.

A physical change is a temporary change in which only the physical properties of the substance are changed. On reversing or removing the cause of the change, the substance regains its original form.

Experiments to Examine Changes in a Few Substances

The changes are temporary in nature and can be reversed. Such changes are called physical changes.

Experiment: By putting around \(2\,{\rm{g}}\) of candle wax in a dry hard glass test tube. With the use of a Bunsen burner flame, slowly melt the wax in a test tube. What are your observations?

When the wax melts, it turns into a colourless liquid. Hold the test tube in cold water to cool it down. What are your observations?

The molten wax hardens. As a result, we can state that wax melts when heated, and liquid wax solidifies when cooled.

Experiment: By using tongs to hold a short piece of platinum or nichrome wire. In a non-luminous Bunsen flame, hold the wire’s end. What are your observations?

The wire’s end gets red hot. Remove the wire end from the Bunsen flame and set it aside to cool. What are your observations?

The colour of the wire returns to its previous state.

Similarly, when electricity passes through a light bulb, the filaments become white-hot and emit light. When the electricity is turned off, the filament produces no light. As a result, the bulb’s look change is only transitory.

Characteristics of Physical Changes

(i) No new substances are formed during a physical change

When ice is heated, it melts and turns into water. When the water is heated further, it turns into steam. The steam condenses and becomes water when it cools. The water forms into ice as it cools further.

Ice, water, and steam molecules, always have two hydrogen atoms and one oxygen atom. As a result, we can conclude that no new substances are formed.

When we add ordinary salt to the water, a salt solution is formed, but no change in the molecules occurs. Water evaporates during evaporation, leaving the salt behind.

(ii) Physical changes can be generally reversed

When a permanent magnet is stroked across a piece of iron, it becomes magnetic. Magnetized iron, on the other hand, loses its magnetic when hammering. When the wax is heated, it turns into a liquid. However, when liquid wax cools, it solidifies.

(iii) There is no change in weight during a physical change

When ten grams of solid wax is melted, it yields \(10\) grams of molten wax.

If you make a salt solution by dissolving \(20\,{\rm{g}}\) salt in water, you’ll end up with \(20\,{\rm{g}}\) of salt after the water evaporates.

(iv) Only a little heat (if any) is absorbed or given off during physical change

If the water absorbs a particular quantity of heat energy to become steam, steam will give off the same amount of heat energy to become water. The heat energy generated during physical changes is never used to alter the composition of a substance’s molecules.

Examples of Physical Changes

We have provided some of the common examples of physical changes below:

1. Preparing a solution of salt and sugar.
2. Powdering chalk stick.
3. Powdering crystals of salt and sugar.
4. Changing of water into steam by boiling
5. Magnetisation of iron.
6. Condensation of water vapour, such as the formation of clouds, mist, fog, etc.

Chemical Changes

A chemical change is a permanent change in which the chemical composition of a substance is changed, and one or more new substances with different chemical compositions and different properties are formed. The change is not easily reversible. e.g., burning of carbon, burning of sulphur, burning of wax, burning of carbon, curdling of milk, digestion of food etc.

Experiment-1: Hold a short length (about \(50\,{\rm{cm}}\)) of magnesium ribbon in the fire tongs-heat the magnesium ribbon in the non-luminous flame for about \(2\) minutes.

The magnesium ribbon produces a bright white flame that produces a lot of heat and light. It leaves white ash behind, which is generally referred to as magnesium oxide.

The magnesium oxide so form does not change to magnesium ribbon on cooling. Thus, we can conclude; the change brought about in magnesium is permanent in nature; a new product is formed with entirely different properties, and a large amount of heat and light energy is evolved..

Experiment-2: \(2\,{\rm{g}}\) of sugar are placed in a hard glass test tube. Strongly heat the test tube. What are your observations?

When the sugar melts, it turns brown. It emits steam when heated further, which condenses on the cooler areas of the test tube. The residue in the test tube has a dark colour to it. The alteration does not reverse after it cools.

As a result, sugar heating is a permanent change. Sugar decomposes into charcoal, which is a type of carbon that is black. It also emits steam, which is made up of water.

Characteristics of Chemical Changes

A change in which the original property of a substance being used is changed to new material with new properties. The change cannot be reversed. Some examples are:

(i) When a chemical change occurs, new substances with entirely new properties are formed

The burning of wax in a candle is a chemical change producing carbon, carbon dioxide and water vapour. This change is not reversible. We do not get wax back from carbon, carbon dioxide and water by cooling them or any other method.

(ii) A chemical change cannot be easily reversed

Heat some sugar crystals in a test tube over a flame. Gradually, the crystal sugar changes its colour to brown. This brown substance is caramel. Caramel is a different substance from white crystal sugar, which has undergone a chemical change. On further heating, the caramel in the test tube forms a black substance. This is mainly carbon.
Sugar on heating gives out water vapour and carbon. Water and carbon do not taste sweet, and we do not obtain sugar back from caramel or carbon by adding water to it. In this change, sugar changes to new substances and the process are not reversed by reversing the cause. This is a chemical change.

(iii) There is usually a change in weight during a chemical reaction

When magnesium is burnt in the air, then the weight of white ash (magnesium oxide) is more than magnesium metal.

Similarly, when iron rusts, the weight of rusted iron is more than that of the original metal because oxygen combines with iron.

(iv) A lot of heat is usually given off or absorbed during a chemical change

• Magnesium produces a lot of heat and light energy as it burns in the air.
• Mercuric oxide absorbs a lot of heat energy when it decomposes into mercury and oxygen.
• Sugar absorbs a lot of heat energy when it decomposes into sugar charcoal and steam.

Examples of Chemical Changes

Below we have provided some of the common examples of chemical changes:

1. Cooking of food
2. Food turning bad after a few days
3. Curdling of milk
4. Fading the colours of clothes
5. Ripening of fruits
6. Lightening of a matchstick by striking match head with the side of Matchbox
7. Digestion of food within our bodies
8. Respiration by humans, plants and animals

Difference between Physical and Chemical change

Below we have listed down the difference between physical and chemical change for your reference:

Summary

Physical or Chemical changes are noticed in the matter when the energy in any form, say light, heat, electricity etc., is either absorbed or released by the matter to show some sort of changes. A temporary change that can be reversed is a physical change. A physical change is a change in shape, size, colour or state. A change in which the original property of a substance being used is changed to new material with new properties. The change cannot be reversed. In this article, we learned about physical changes and chemical changes, characteristics of physical and chemical changes and examples.

FAQs on Physical Changes and Chemical Changes

Q.1. What are five physical changes and chemical changes?
Ans: The 5 Physical and Chemical changes are explained below.
Some common examples of physical changes are:
1. Preparing a solution of salt and sugar.
2. Powdering chalk stick.
3. Condensation of water vapour, such as the formation of clouds, mist, fog, etc.
4. Changing of water into steam by boiling
5. Magnetization of iron.
Some common examples of chemical changes are:
1. Cooking of food.
2. Food turning bad after a few days.
3. Curdling of milk.
4. Fading the colours of clothes.
5. Ripening of fruits.

Q.2. What is an example of both a physical and chemical change?
Ans: Cutting wood is a physical change, as no new substance is formed. There is no evolution of heat and light.On the other hand, the burning of wood is a chemical change, as a new substance is formed, called ash, with an evolution of heat and light. It is an irreversible process.

Q.3. What is a chemical change and physical change?
Ans: A physical change is a temporary and easily reversible change in which the physical properties (e.g., physical state, shape, size, appearance, density etc.) of a substance change. A chemical change is a permanent change in which the chemical composition of a substance is changed, and one or more new substances with different chemical compositions and different properties are formed. The change is not easily reversible.

Q.4. Is boiling an egg a chemical change?
Ans: A chemical change occurs when an egg is boiled. The composition of an egg is irreversible when it is cooked. As a result of the formation of new material, it is irreversible.

Q.5. Can a physical and chemical change occur together?
Ans: Yes, physical and chemical changes can occur simultaneously in some circumstances. The burning of a candle is one such example. The melting of wax and the solidification of molten wax are physical changes. The burning of molten wax is a chemical change.

We hope this article on Physical and Chemical Changes has helped you. If you have any queries, drop a comment below, and we will get back to you.