Types of chemical Reactions

In the first blog of the series, we talked about chemical reactions. We know from the blog that a chemical reaction is a process in which atoms or molecules of one or more substances are rearranged to form new substances. Today we are going to discuss types of chemical reactions.

In a chemical reaction, the transformation of atoms from one element to another does not occur. Likewise, atoms do not vanish from the mixture or materialize from elsewhere. Rather, chemical reactions entail the process of breaking and forming bonds between atoms, resulting in the creation of new substances.

The process of breaking and forming bonds can be carried out by different types of chemical reactions. Today we are going to discuss only two of them. The first one is.

 

Combination Reaction

A combination reaction, also known as a synthesis reaction, occurs when two or more substances combine to form a single, more complex substance. In a combination reaction, the reactants react with each other to create a product.

 The general equation for a combination reaction is:

A + B → AB

Here, A and B represent the reactants, and AB stands for the product.

For example, let’s discuss the formation of Water (H₂O)

2H₂ + O₂ → 2H₂O

We can clearly see that two molecules of hydrogen gas (2H₂) are combining with one molecule of oxygen gas (O₂) to form one molecule of water (H₂O).

Let’s take one more example. The formation of Calcium Oxide (CaO)

2Ca + O₂ → 2CaO

In this example we can see that two molecules of Calcium metal (2Ca) are reacting with one molecule of oxygen gas (O₂) to form two molecules of calcium oxide (2CaO).

These are just a few examples of combination reactions. In combination reactions, the reactants combine to produce a new substance with different properties than the individual reactants.

It has been seen that sometimes during the chemical reaction heat evolves along with the formation of products. The reaction in which such kinds of phenomenon is seen is known as exothermic chemical reaction.

 

Exothermic chemical reaction

An exothermic chemical reaction is a type of reaction that releases energy in the form of heat to its surroundings. In an exothermic reaction, the products have lower energy than the reactants, resulting in the release of excess energy. This energy is often seen as an increase in temperature or the generation of heat.

There are several examples of exothermic reactions such that:

• Combustion Reactions: Burning of fuels such as wood, gasoline, or natural gas.
• Neutralization Reactions: The reaction between an acid and a base to form salt and water. This reaction often generates heat.
• Oxidation Reactions: Reactions where a substance combines with oxygen. These reactions often release energy in the form of heat.

These are examples of exothermic reactions releasing energy in the form of heat during the chemical process. It is important to note that not all chemical reactions are exothermic.

 

The second type of chemical reaction is;

Decomposition reaction

A decomposition reaction is a type of chemical reaction in which a compound breaks down into simpler substances. It is the opposite of a combination reaction. In a decomposition reaction, a single reactant decomposes or breaks apart to form two or more products. The general equation for a decomposition reaction is:

AB → A + B

Here, AB stands for the reactant, while A and B represent the products formed during the decomposition.

For example, let’s discuss the Decomposition of Water (H₂O)

When water is subjected to high temperatures, it decomposes into its constituent elements, hydrogen gas (H₂) and oxygen gas (O₂). Here we can see that at high temperature two molecules of water are breaking apart into two molecules of hydrogen (2H₂) and one molecule of oxygen (O₂).

Another example of decomposition reaction can be taken is Hydrogen Peroxide (H₂O₂)

2H₂O₂ → 2H₂O + O₂

Hydrogen peroxide decomposes spontaneously over time or can be accelerated by adding a catalyst. It decomposes into water (H₂O) and oxygen gas (O₂).

We can see that two molecules of hydrogen peroxide (2H₂O₂) are decomposing into 2 molecules of water (H₂O) and one molecule of oxygen gas (O₂).

These examples illustrate decomposition reactions in which a single compound breaks down into simpler substances.

In the first example of decomposition reaction, we discussed that water needs high temperature to decompose into simpler substances. The decomposition reaction that requires heat energy to process is known as thermal decomposition reaction.

 

Thermal decomposition reaction

A thermal decomposition reaction is a specific type of decomposition reaction that is initiated or driven by heat. In thermal decomposition reactions, a compound breaks down into simpler substances when exposed to high temperatures. The heat energy supplies the activation energy required for the reaction to occur.

Some examples of thermal decomposition reaction are:

1. Thermal Decomposition of Calcium Carbonate (CaCO₃):

CaCO₃ (s) → CaO (s) + CO₂ (g)

When calcium carbonate (commonly found in limestone or marble) is heated, it decomposes into calcium oxide (quicklime) and carbon dioxide gas.

 

2. Thermal Decomposition of Hydrogen Peroxide (H₂O₂):

2H₂O₂ (l) → 2H₂O (l) + O₂ (g)

Hydrogen peroxide decomposes into water and oxygen gas when heated.

These examples highlight thermal decomposition reactions in which the application of heat causes the compounds to decompose into simpler substances. It is important to note that specific conditions, such as temperature, pressure, and presence of catalysts, can significantly influence the rate and outcome of thermal decomposition reactions.

 

Third type of chemical reaction is;

Displacement Reaction

A displacement reaction, also known as a substitution reaction, is a type of chemical reaction in which one element or group of elements is replaced by another element in a compound. It occurs when a more reactive element displaces a less reactive element from its compound. The less reactive element is typically pushed out of the compound and is often in the form of a cation (positively charged ion) or an anion (negatively charged ion).

A reactive element can be defined as the compatibility of both elements to form bonds. The more compatible the elements will be, the more readily they will form bonds.

Displacement reactions can occur in various forms, such as metal displacement reactions, halogen displacement reactions, and redox reactions. Here are a few examples to illustrate different types of displacement reactions:

 

1. Metal Displacement Reaction: In a metal displacement reaction, a more reactive metal displaces a less reactive metal from its compound. For example:

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

 

In this reaction we can observe that zinc (Zn) reacts with copper sulphate and displaces copper (Cu) from copper sulfate (CuSO₄), resulting in the formation of zinc sulfate (ZnSO₄) and solid copper.

 

2. Halogen Displacement Reaction: Halogen displacement reactions involve the displacement of one halogen by another halogen in a compound. For instance:

 

Cl₂ (aq) + 2Na Br (aq) → 2Na Cl(aq) + Br₂ (l)

 

In this reaction we can observe that chlorine (Cl₂) reacts with sodium bromide and displaces bromine (Br) to form sodium chloride (NaCl) and liquid bromine.

These are examples of displacement reactions. Displacement reactions are important in various fields, including metallurgy, electrochemistry, and chemical synthesis. They help us understand the reactivity of different elements and provide a means for obtaining desired products through the replacement of specific elements in compounds.

 

 

Fourth type of chemical reaction is;

Double Displacement reaction

A double displacement reaction, also known as a double replacement or metathesis reaction, is a type of chemical reaction that involves the exchange of ions between two compounds. In this reaction, cations and anions of two different compounds swap places, resulting in the formation of two new compounds.

The general form of a double displacement reaction can be represented as:

AB + CD → AD + CB

In this equation, A and C represent cations, while B and D represent anions. The cations and anions recombine to form new compounds, AD and CB.

Here's an example to illustrate a double displacement reaction:

NaCl (aq) + AgNO₃ (aq) → NaNO₃ (aq) + AgCl (s)

 

In this reaction we can see that sodium chloride (NaCl) and Silver Nitrate (AgNO₃) are reacting. In reaction chlorine (Cl) and Nitrate (NO₃) swapped their place and produced two new elements sodium nitrate (NaNO₃) and silver chloride (AgCl).

Double displacement reactions often occur in aqueous solutions where the ions are free to move and interact. They are commonly observed in reactions involving ionic compounds, such as salts, acids, and bases.

Fifth type of chemical reaction is; 

Redox Reaction

It involves two simultaneous processes: oxidation, which involves the loss of electrons, and reduction, which involves the gain of electrons. Redox reactions are essential for energy generation, chemical transformations, and numerous biological processes.

In a redox reaction, there are two key components:

1. Oxidation: Oxidation refers to the process in which a substance loses electrons, resulting in an increase in its oxidation state. It is often associated with the addition of oxygen or the removal of hydrogen from a compound. The substance that undergoes oxidation is called the reducing agent or reductant since it causes the reduction of another species.
2. Reduction: Reduction refers to the process in which a substance gains electrons, leading to a decrease in its oxidation state. It is typically associated with the addition of hydrogen or the removal of oxygen from a compound. The substance that undergoes reduction is called the oxidizing agent or oxidant since it causes the oxidation of another species.

A simplified representation of a redox reaction can be given using half-reactions, where oxidation and reduction are written separately. Each half-reaction consists of the species involved and the electrons gained or lost. The overall redox reaction can be obtained by balancing the number of electrons transferred in both half-reactions.

For example, let's consider the reaction between magnesium (Mg) and oxygen (O₂) to form magnesium oxide (MgO):

2Mg + O₂ → 2MgO

In this reaction, magnesium is oxidized (loses electrons) to form Mg²⁺ ions, while oxygen is reduced (gains electrons) to form O²⁻ ions. The oxidation half-reaction is:

Mg → Mg²⁺ + 2e⁻

The reduction half-reaction is:

O₂ + 4e⁻ → 2O²⁻

 By balancing the number of electrons transferred, the overall redox reaction is obtained. The overall redox reaction is:

2Mg + O₂ → 2MgO

 

Effects of oxidation reaction:

Oxidation reactions have several effects and consequences in various contexts. Here are two of the obvious effects of oxidation reactions:

1. Corrosion: Oxidation reactions can cause the deterioration of materials through corrosion. When metals react with oxygen and other substances in the environment, they can undergo oxidation, leading to the formation of metal oxides or other corrosion products. Corrosion can weaken structures, reduce the lifespan of materials, and affect their functionality.
2. Preservation and Food Spoilage (Rancidity): Oxidation reactions can influence the preservation and spoilage of food. Oxidation of fats and oils in food can lead to rancidity, causing undesirable flavors and odors. Antioxidants are often used to inhibit oxidation and extend the shelf life of food products.