Chemical changes generally happen when two substances react or combine with each other to form a different substance.
When any two or more substances in matter react with one another, two kinds of changes occur: Physical change which is usually reversible and chemical change which is generally irreversible. In this section, we’ll try to understand in detail about the chemical changes taking place in matter and the chemical change examples.
Irreversible processes are the processes in which the matter cannot be brought back into its initial form as the molecular structure of the matter partially or entirely changes.
Properties of chemical change
We can determine if the matter has gone through a chemical change or not with the help of the following properties:
- If the molecular composition of the matter/ substance changes.
- If the light is produced.
- If there is a change in temperature of the matter as energy is either released or absorbed when changes in molecular composition occur.
- When the energy is released, it is known as an exothermic reaction.
- When the energy is absorbed, it is known as an endothermic reaction.
- If the sound is produced.
- If there is a change in mass of the reactants present in the substance.
- If there is a change in composition.
- If gas is produced.
- If the color of the substance changes.
- If a precipitate is formed.
- In the case of liquids, bubbles may form.
- If an odor is released.
- If the change is difficult to reverse or impossible to reverse.
A chemical change might not display all the signs, but a few are likely to occur.
Types of chemical change
The types of chemical changes are divided into three main categories:
- Organic changes
- Inorganic changes
- Bio-chemical changes
Further, let us have a close look at these three changes:
1. Organic Changes
‘Carbon’ – one of the most important components of organic chemistry and hence the organic change.
Changes concerned with the chemistry of carbon and elements or compounds with which it reacts are known as Organic Chemistry.
Thus, when a substance undergoes a change involving carbon and its compounds, it is known as organic chemical change or simply organic change.
Some typical examples of organic changes involve:
- Cracking of hydrocarbons from crude oil for making gasoline at an oil refinery.
- Halogenations, which means reactions that deal with elemental halogens like Fluorine (F), Chlorine (Cl), Iodine (I), Bromine (Br), etc.
- Condensation reaction in which a single molecule is formed from the combination of two or more molecules. Usually, there is a loss of water when this type of reaction occurs; it is known as condensation reaction.
- Methylation, which means adding a methyl group to a substrate.
- Polymerization, which includes the reaction of monomer molecules to form a polymer chain in 3-dimensional networks.
2. Inorganic change
Reactions that do not involve ‘carbon’ are known as inorganic reactions and hence inorganic chemical change or simply inorganic change.
The typical types of reactions that inorganic changes involve are:
- Mixing of acid with a base, generally known as neutralization.
- Redox reactions in which there is a shift in oxidation states of atoms due to oxidation or reduction.
- Decomposition reaction in which a compound breaks down into two or more substances.
- Displacement reactions in which an atom or ion of one compound replaces an atom or ion of another compound.
3. Biochemical Change
It is a chemistry that occurs in living organisms such as plants, animals, humans, microorganisms, etc., where enzymes and proteins control most reactions.Biochemical change is highly complex, and it is still not fully understood.
Typical types of biochemical changes involve:
- Photosynthesis is a process used by plants, algae, and cyanobacteria (a group of bacteria) to convert light energy that is generally received from sunlight to convert into chemical energy so that it can be later used to fuel the organism’s activities.
- Protein synthesis, which creates protein in molecules that helps in the growth of the organism.
- Krebs cycle, which is a process that releases stored energy derived from proteins, fats, and carbohydrates through oxidation.
- Digestion is a process in which large food molecules are broken down into small food molecules so that they can be absorbed into blood plasma which helps the body to move and grow.
Read more on Example of Static force
Chemical Change Examples
1. Rusting Iron
Rusting is a chemical process that happens when iron or its alloys come in contact with oxygen in the presence of moisture, and hence it is a type of Redox reaction known as oxidation.
Objects submerged in the sea tend to rust faster due to the presence of salt in the seawater through the electrochemical process.
As rusting is a type of irreversible chemical change, iron cannot be brought back into its original form, but it can sure be prevented from rusting by using non-rusting materials or slow rusting materials as a protective coat on deteriorating materials, by galvanizing the material, or by coating the material by painting, wax tapes, varnish, and lacquer.
2. Cooking Food
Cooking food is the simplest example of chemical change. For cooking any food, the raw ingredients are either boiled, fried, baked or sautéed. In any case, there is a change in its chemical composition, which cannot be reversed back. When the raw ingredients are cooked, there is a change in flavor, color, nutritional composition, etc.
3. Digestion of food in the stomach
When the food that we eat reaches the stomach, it mixes with several digestive juices and enzymes that the stomach makes. The stomach’s strong muscles blend the food with enzymes and digestive juices to turn the food into a usable form. Once this process is completed, the food slowly enters the small intestine via a short tube between the stomach and the small intestine. Here the next step takes place when the juices produced in the pancreas and liver turn the food into energy. As a result, a lot of processes take place that completely change the food’s chemical composition. And thus, digestion of food is a chemical change.
4. Burning wood
Burning of wood is an example of chemical reaction as the structure and chemical composition of the wood change as a whole. Oxygen is an essential component when it comes to igniting something. In the absence of oxygen, the material would not catch fire or would not get ignited. So, when the wood log is kindled, it turns into ashes releasing carbon dioxide and water vapor.
5. Fruit/Vegetable getting rotten
There are multiple reasons behind fruit/vegetables or any food getting rotten, such as prolonged exposure of food in closed spaces in the presence of moisture, fermenting, acidifying, etc. Such processes create bacteria and fungi that sometimes cannot be harmful themselves, but their waste products may cause severe implications to one’s health.
6. Decomposition of matter into the soil
Decomposition is a process that breaks down large pieces of matter into smaller ones. It is affected by several factors such as the soil’s surface, temperature, accessibility to flies or insects, oxygen, humidity, composition, and the matter’s internal components. The rate of decomposition also varies due to all such factors.
Various chemical powders are filled inside a firecracker, which, when set to fire, react with each other producing different types of sound, color, lighting and patterns. For a firecracker to burn with its expected result, it needs some amount of energy known as Activation Energy . Once the tip of the firecracker is ignited, heat is produced that provides the required activation energy to the firecracker to show its beautiful result in the form of lighting and color.
Still, with this stunning effect, there comes a severe issue, that is the release of toxic chemicals into the atmosphere such as carbon monoxide, potassium, nitrogen, carbon dioxide, ammonia, etc., that create air pollution, which in turn has adverse effects on human health, animals and plants. Also, various institutions are researching to make an Eco-friendly alternative to firecrackers.
Photosynthesis is a process used by plants and other organisms to convert light energy received from sunlight into chemical energy that can further fuel the body’s movement and growth. This energy is stored in starch and sugars present in the particular body. Plants absorb Carbon Dioxide and water from the surrounding environment like air and soil and, in turn, emit oxygen in the presence of light which acts as a catalyst.
A general equation for photosynthesis in plants is given as:
A light-absorbing pigment known as chlorophyll, responsible for giving the green colour in plants absorbs energy from blue-light and red-light and reflects the green-light, making the plant appear green.
Thanks to plants for which oxygen is a waste, due to which all life forms on earth can breathe.
9. Leaves changing color
Many factors affect the change in color of leaves. One such is the breaking down of chlorophyll pigments, due to which plants lose their green color. When chlorophyll breaks down, another pigment known as Anthocyanin, responsible for the red color in leaves, comes to the rescue that protects the leaves from harmful sun-rays. But this doesn’t last for an extended period of time; eventually, these leaves dry out and fall off. Similarly, different pigments are responsible for different colors in plants.
Some other reasons for leaves changing color are drought, disease, change in the soil pH level, too little or too much availability of water and root damage.
One of the most famous and easy examples of this reaction is the mixture of Hydrochloric acid with Sodium Hydroxide, which is a base, both in aqueous form, that yields Sodium Chloride and water.
Its reaction can be given as follows:
Hydrochloric Acid (HCL) + Sodium Hydroxide (NaOH)→Sodium Chloride (NaCl) + Water(H2O)
The reaction between an acid and a base is one of the most important chemical change examples.