essay on chemical and physical changes

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Chemical and Physical Changes of Matter

If you are confused about chemical and physical changes and how to tell them apart, you’ve come to the right place. Chemical and physical changes both are changes in the structure of matter . In a chemical change , a chemical reaction occurs and a new substance is produced. In a physical change , matter changes forms but does not change its chemical identity. So, the difference between chemical and physical changes is that a chemical change alters the chemical composition of matter, while a physical change does not

A chemical change produces a new substance, while a physical change alters the form of matter but not its chemical identity.

Chemical Changes

A chemical change involves a chemical reaction to produce a new product . It is a change at the molecular level of matter. Chemical bonds between atoms break and then form to connect different atoms.

Examples of Chemical Changes

In a chemical change, new product forms as atoms rearrange themselves. Chemical bonds are broken and reform to make new molecules. Examples of chemical changes include:

• Souring milk
• Digesting food
• Cooking an egg
• Baking a cake
• Rusting iron
• Mixing an acid and a base
• Burning a candle
• Mixing baking soda and vinegar

Physical Changes

A physical change is a change in matter that alters its form but not its chemical identity. The size or shape of matter often changes, but there is no chemical reaction. Phase changes are physical changes. These include melting, boiling, vaporization, freezing, sublimation and deposition. Breaking, crumpling, or molding matter also results in a physical change. Many physical changes are reversible.

• Examples of Physical Changes

Examples of physical changes include:

• Melting an ice cube
• Freezing an egg
• Boiling water
• Sublimation of dry ice into carbon dioxide gas
• Shredding paper
• Crushing a can
• Breaking a bottle
• Chopping vegetables
• Mixing sand and salt
• Making sugar crystals
• Dissolving sugar in water (the sugar mixes with the water, but can be recovered by evaporation or boiling)

How to Tell Chemical and Physical Changes Apart

The key to distinguishing between chemical and physical changes is determining whether there is a new substance that wasn’t there before. If you see signs of a chemical reaction, it’s probably a chemical change. Signs of a reaction include:

• Temperature change
• Color change
• Formation of a precipitate

If none of these signs are present, it’s a good bet a physical change occurred.

Are Physical Changes Reversible?

Some people use reversibility as a test for chemical and physical changes. The premise is that a physical change can be undone, while a chemical change can only be reversed by another chemical reaction. This is not a great test because there are too many exceptions. While you can melt and freeze an ice cube (a physical change), it’s much harder to reassemble shredded paper (another physical change).

Most physical changes can be reversed if energy is added. Some chemical changes are reversible, but only via another chemical reaction. For example, rusting of iron is a chemical change. Converting rust back into iron and oxygen is possible, but it requires a chemical reaction.

Practice Identifying Chemical and Physical Changes

Download and print this worksheet for practicing identifying chemical and physical changes. The worksheet and answer key are PDF files, or you can right-click, save, and print the PNG image.

[ PDF Worksheet ] [ Answer Key ]

Explore chemical and physical changes in greater detail and learn how they relate to chemical and physical properties of matter:

• Examples of Chemical Properties
• Is Dissolving Salt a Chemical or Physical Change?
• Examples of Physical Properties
• Atkins, P.W.; Overton, T.; Rourke, J.; Weller, M.; Armstrong, F. (2006).  Shriver and Atkins Inorganic Chemistry  (4th ed.). Oxford University Press. ISBN 0-19-926463-5.
• Chang, Raymond (1998).  Chemistry  (6th ed.). Boston: James M. Smith. ISBN 0-07-115221-0.
• Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001).  Organic Chemistry  (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
• Kean, Sam (2010).  The Disappearing Spoon – And Other True Tales From the Periodic Table . Black Swan, London. ISBN 978-0-552-77750-6.
• Zumdahl, Steven S.; Zumdahl, Susan A. (2000).  Chemistry  (5th ed.). Houghton Mifflin. ISBN 0-395-98583-8.

Related Posts

• Physical and Chemical Changes
• Difference Between Physical And Chemical Change

Difference Between Physical and Chemical Change

There are many differences between physical and chemical changes and it is important to understand them to be able to understand these concepts clearly. The comparisons and differences between physical and chemical changes are given below along with their examples. To understand physical and chemical properties and changes better, it is important to know what they are. Visit physical and chemical changes to know more about them in detail. In this article, the differences between physical changes and chemical changes are provided in a tabular format.

Table of Contents

Differences between physical and chemical change.

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• Frequently Asked Questions – FAQs

Thus, it can be understood that the primary difference between physical and chemical changes is that physical changes are reversible, whereas chemical changes are usually not.  To learn more about how physical and chemical changes are different, register with BYJU’S now!

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Physical and chemical changes and its characteristics.

Reversible and Irreversible Changes

Frequently Asked Questions – FAQs

How can you tell the difference between physical and chemical changes.

The appearance or form of matter changes during a physical change, but the type of matter in the substance does not. A chemical change, on the other contrary, results in the creation of at least one new substance with new properties.

Why is it important to know the difference between physical and chemical changes?

It’s essential to recognise the difference between chemical and physical changes. Several changes are obvious, but there are some fundamental concepts to be aware of. Physical changes usually refer to changes in the physical state of stuff. When two or more molecules interact, chemical changes occur on a molecular level.

What are the examples of physical and chemical changes?

Examples of chemical changes would be burning, cooking, rusting, and rotting. Examples of physical changes could be boiling, melting, freezing, and shredding. Most physical changes can be reversed if sufficient energy is provided.

How to tell whether it’s a physical or chemical change?

Check for indications that a chemical change has taken place. The following are indications of a chemical change:

• Gas is created. Bubbles can occur in liquids.
• An odour is created.
• The colour of the substance changes.
• Sound is generated.
• There is a shift in the temperature. The environment either heats up or cools down.
• Light is generated.
• A precipitate develops.
• Reversing the change is difficult or impossible.

What are three forces that can cause a physical change?

Forces such as motion, temperature, and pressure can create physical changes. Oxygen in the air reacts with sugar, and the chemical bonds are destroyed.

Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin!

Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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Are rotting vegetables an example of a physical or chemical change? Or is it neither?

Decaying plant and rotting vegetables is another chemical reaction, because this reaction is non-reversible. Also because the decomposition of the plant changes the chemical formulas of the compounds in the plant.

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Changes in Matter: Physical vs. Chemical Changes

Physical changes do not produce a new substance. Chemical changes result in the production of a new substance and cannot be reversed.

Oxidized Copper Lion

The process of rusting, or oxidization, exemplifies a chemical reaction. Here is an oxidized copper lion statute in front of the Chicago Art Institute and the Aon Center.

Photograph by Paul Damien

Matter is capable of undergoing changes, which are classified as either physical or chemical. Physical changes in matter are often reversible. For example, an ice cube can melt into liquid water, and then the liquid water can be refrozen into an ice cube. Chemical changes , on the other hand, are not reversible: A log burned in a fire turns to ashes, but the ashes cannot be changed back into a log. What Is a Physical Change? In a physical change, the material involved is structurally the same before and after the change. Examples of some physical changes are texture, shape, temperature, and a change in the state of matter. A change in the texture of a substance is a change in the way it feels. For instance, a block of wood may feel rough when you run your finger across it. If you rub that block of wood with sandpaper to smooth the surface, it will no longer feel rough. The wood itself has not changed during sanding to become a new material, though—only the texture of the surface changed. A piece of metal may be heated in a fire until it glows, but the metal is the same material before heating and after cooling. Similarly, when a material changes phase, it only changes physically; the substance is still the same. Think about ice melting into water, and then water being heated up and turning into steam. The chemical structure of water is the same whether it is a solid (ice), liquid, or gas (steam). What Is a Chemical Change? A chemical change occurs when the composit ion of a substance is changed. Chemical changes require the breaking and forming of chemical bonds during a chemical reaction . This results in the rearranging of atoms in substances to form the products of a chemical reaction, which become brand new molecules . These new molecules cannot be easily reverted back to their original state. Sometimes it is difficult to tell if a chemical reaction has taken place. To help determine whether there has been a reaction, chemists consider a few basic indicators. These include a change in temperature, a change in color, or the development of an odor. The formation of a precipitate or the formation of a gas may also indicate a chemical reaction. In a chemical alteration, a temperature change occurs as a result of the breaking or formation of chemical bonds. When the chemical bonds of the reactants are broken, sometimes excess energy is released. This can cause heat to be discharged, leading to an increase in temperature. Burning wood is an example of a reaction that releases excess energy as heat. A chemical cold pack in a first aid kit is an example of a chemical reaction that absorbs heat energy, rather than releasing it. This results in cooling. An example of a color change signaling a chemical reaction can be observed when iron reacts with oxygen to produce iron oxide. A common example is when an iron nail is left outside. Over time, it develops a reddish-brown rust. Rotting food illustrates odor development as a result of a chemical change. When food spoils it may produce a foul odor. This is because of chemical reactions that take place as the food begins to break down and go bad. These changes lead to the formation of new substances that have unique smells. Another common sign of a chemical reaction is the formation of a precipitate. This happens when chemicals dissolved in a solution are mixed together and an insoluble solid forms in the liquid mixture. This solid is a precipitate. The creation of a new, solid substance from two liquid substances indicates that a reaction has taken place that has altered the original substances. A chemical reaction may also release a gas. For example, a mix of vinegar and baking soda will immediately start bubbling and foaming. The bubbles are a release of carbon dioxide gas, a product of the chemical reaction between these two household substances. Chemical Change or Physical Change? Sometimes it is difficult to determine whether a change is physical or chemical. For example, think about dissolving table salt (sodium chloride) into liquid water. The solid table salt is added to the water and disappears. This dissolution is easily identified as a physical change, because if the water is allowed to evaporate, the salt remains after all the water has evaporated. In other words, the salt has not been permanently altered. However, table salt is an ionic compound. Ions are negatively or positively charged atoms or molecules (because of the loss or gain of an electron). When ionic compounds are added to water, they dissociate or break apart into ions. In the case of table salt, salt added to water dissociates into sodium ions (positive) and chloride ions (negative). This would seem to be a chemical change. However, scientists do not consider this to be one, because the solid table salt remains after the water is evaporated. The atoms recombine into their original arrangement once the water is removed. The formation of alloys is another example of a change that is difficult to identify as either physical or chemical. An alloy is a metal that has different properties from the metals that are mixed together to make it. Brass is a common example, which can be found on musical instruments such as trumpets, trombones, and saxophones. Brass is made up of about 60 percent copper and 40 percent zinc. However, brass has different properties than either copper or zinc alone. Brass, though, is not made using a chemical reaction. The copper and zinc atoms are both in brass, but they do not chemically bond together. As a result, brass represents a physical change instead of a chemical change. Remember that a physical change is a change in properties such as texture, shape, or state. In contrast, a chemical change represents the formation of a new substance after the atoms are rearranged by means of a chemical reaction. Unlike many physical reactions, a chemical reaction cannot be easily reversed and sometimes cannot be reversed at all.

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Physical and Chemical Changes

Key questions.

A chemical change is any change that results in the formation of new chemical substances with new properties.

For example, hydrogen reacts with oxygen to form water. This is a chemical change.

2H₂ + O₂ → H₂O

Hydrogen and oxygen are both colourless gases, but water is a liquid at ordinary temperatures.

Which of the following are chemical changes? (a) Sugar dissolves in warm water. (b) A nail rusts. (c) A glass breaks. (d) A piece of paper burns. (e) Iron and sulfur form a shiny nonmagnetic grey substance on heating.

Solutions :

(a) Not a chemical change. The sugar and water are still present. (b) A chemical change. The reddish-brown rust is different from the iron. (c) Not a chemical change. The glass is just in smaller pieces. (d) A chemical change. The paper disappears. All that remains is a small amount of ash. (e) A chemical change. Sulfur is yellow, and iron is magnetic. The product is neither yellow nor magnetic.