Fast And Slow Chemical Reactions

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Slow reactions

Chemical reactions that occur very slowly and can take a long time for completion are called slow reactions.  
Usually covalent compounds are involved in slow reactions.
Some reactions can take days, weeks and months to complete; they are called very slow reactions.
For example, Milk may take several hours or a day to convert to curd, while it may take even longer for iron to corrode.

Rusting of Iron
4Fe + 3O2       ->    2Fe2O3
                              (Iron) (Oxygen)      (Rust – Iron Oxide)

Formation of crude oil by a geochemical reaction and disintegration of radium are other examples of slow reactions.


Fast reactions

Chemical reactions that complete in a very short time, such as less than 10 -6 seconds, they are called fast reactions.
Examples: Magnesium ribbon is burnt in the flame of Bunsen burner; it quickly gets combusted with a noticeable spark.

2Mg(s) + O2 (g) heat > 2MgO (s)

Similarly, a neutralization reaction between acids and bases is a fast reaction.
Example: When hydrochloric acid reacts with the base, ammonium hydroxide, it forms salt and water.

HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O (l)
(Acid)        (Base)             (Common Salt) (Water)

Another example of fast reaction is formation of silver chloride precipitate when sodium chloride solution is mixed with silver nitrate solution.
Ag+NO3- + Na+Cl– -> AgCl + NaNO3

Since, these fast reactions occur between ions, they are also known as ionic reactions. 
Besides slow and fast reactions, there is another category called moderate reactions.

 


Irreversible Reactions

A fundamental concept of chemistry is that chemical reactions occurred when reactants reacted with each other to form products. These unidirectional reactions are known as irreversible reactions, reactions in which the reactants convert to products and where the products cannot convert back to the reactants. These reactions are essentially like baking. The ingredients, acting as the reactants, are mixed and baked together to form a cake, which acts as the product. This cake cannot be converted back to the reactants (the eggs, flour, etc.), just as the products in an irreversible reaction cannot convert back into the reactants. 

An example of an irreversible reaction is combustion. Combustion involves burning an organic compound—such as a hydrocarbon—​and oxygen to produce carbon dioxide and water. Because water and carbon dioxide are stable, they do not react with each other to form the reactants. Combustion reactions take the following form:

CxHy+O2→CO2+H2O

 


Reversible Reactions

In reversible reactions, the reactants and products are never fully consumed; they are each constantly reacting and being produced. A reversible reaction can take the following summarized form:

A+B⇌k1k−1C+DA+B⇌k1k−1C+D

This reversible reaction can be broken into two reactions.

Reaction 1: 

A+B−→k1C+DA+B→k1C+D

Reaction 2: 

C+D−→−k−1A+BC+D→k−1A+B

These two reactions are occurring simultaneously, which means that the reactants are reacting to yield the products, as the products are reacting to produce the reactants. Collisions of the reacting Molecules cause chemical reactions in a closed system. After products are formed, the Bonds between these products are broken when the molecules collide with each other, producing sufficient energy needed to break the bonds of the product and reactant molecules. 

Imagine a ballroom. Let reactant A be 10 girls and reactant B be 10 boys. As each girl and boy goes to the dance floor, they pair up to become a product. Once five girls and five boys are on the dance floor, one of the five pairs breaks up and moves to the sidelines, becoming reactants again. As this pair leaves the dance floor, another boy and girl on the sidelines pair up to form a product once more. This process continues over and over again, representing a reversible reaction. 

Unlike irreversible reactions, reversible reactions lead to equilibrium: in reversible reactions, the reaction proceeds in both directions whereas in irreversible reactions the reaction proceeds in only one direction. If the reactants are formed at the same rate as the products, a dynamic equilibrium exists. For example, if a water tank is being filled with water at the same rate as water is leaving the tank (through a hypothetical hole), the amount of water remaining in the tank remains consistent. 

 

Reversible reaction and dynamic nature of equilibrium.

A reversible reaction attains equilibrium of dynamic nature and not of static nature. The fact that the properties of a system become constant at the equilibrium stage may give the impression that both the forward and backward processes stop altogether. This however is not true. At equilibrium, forward and backward reactions go at equal speeds, but do not stop. The rate of formation of the products exactly equals to the rate of formation of reactants again. As a result the concentration of the reactants and products and other properties of the system remain unchanged. Thus the equilibrium is dynamic in nature.

 


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The Rate of a Chemical Reaction is the speed at which the reactants are converted into products. The rate of a reaction can be affected by a number of factors, including the concentration of the reactants, the temperature, the presence of a Catalyst, and the surface area of the reactants.

The concentration of the reactants is one of the most important factors affecting the rate of a reaction. The higher the concentration of the reactants, the more likely it is that the reactant molecules will collide with each other and react.

The temperature is another important factor affecting the rate of a reaction. The higher the temperature, the faster the molecules move. This means that they are more likely to collide with each other and react.

A catalyst is a substance that speeds up the rate of a chemical reaction without itself being consumed. Catalysts work by providing an alternative pathway for the reaction to occur. This pathway has a lower activation energy than the uncatalyzed pathway. The activation energy is the minimum energy required for the reactants to react.

ENZYMES are biological catalysts. They are proteins that speed up the rate of biochemical reactions in living organisms. Enzymes are highly specific, meaning that they only catalyze a specific reaction or group of reactions.

Reversible reactions are reactions that can proceed in both the forward and reverse directions. The equilibrium constant for a reversible reaction is a measure of the relative concentrations of the reactants and products at equilibrium.

Equilibrium is a state of balance in which the rate of the forward reaction is equal to the rate of the reverse reaction. At equilibrium, the concentrations of the reactants and products do not change.

Le Châtelier’s principle states that if a system at equilibrium is disturbed, the system will shift in a way to counteract the disturbance. For example, if the concentration of a reactant is increased, the equilibrium will shift to the right, producing more products.

The kinetics of enzyme-catalyzed reactions are the study of how enzymes speed up the rate of chemical reactions. Enzymes work by providing an alternative pathway for the reaction to occur. This pathway has a lower activation energy than the uncatalyzed pathway.

Inhibitors are substances that slow down the rate of a chemical reaction. Activators are substances that speed up the rate of a chemical reaction.

Enzyme kinetics and drug design are closely related fields. Enzymes are the targets of many drugs. By understanding how enzymes work, scientists can design drugs that will specifically target and inhibit or activate the enzymes involved in a particular disease process.

Here are some examples of fast and slow chemical reactions:

The rate of a chemical reaction can be affected by a number of factors, including the concentration of the reactants, the temperature, the presence of a catalyst, and the surface area of the reactants. By understanding the factors that affect the rate of a chemical reaction, scientists can design experiments to study the rates of reactions and to develop new technologies that rely on chemical reactions.

What is a chemical reaction?

A chemical reaction is a process that changes one or more substances into new substances.

What are the different types of chemical reactions?

There are many different types of chemical reactions, but some of the most common include:

What are the factors that affect the rate of a chemical reaction?

The rate of a chemical reaction is affected by a number of factors, including:

What are some examples of fast and slow chemical reactions?

Some examples of fast chemical reactions include:

Some examples of slow chemical reactions include:

What are some applications of chemical reactions?

Chemical reactions are used in a wide variety of applications, including:

What are some safety precautions that should be taken when working with chemicals?

When working with chemicals, it is important to take the following safety precautions:

  1. Which of the following is not a factor that affects the rate of a chemical reaction?
    (A) Temperature
    (B) Concentration
    (C) Surface area
    (D) Catalyst

  2. The rate of a chemical reaction is the speed at which the reactants are converted into products.
    (A) True
    (B) False

  3. The rate of a chemical reaction can be increased by increasing the temperature, increasing the concentration of the reactants, or increasing the surface area of the reactants.
    (A) True
    (B) False

  4. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.
    (A) True
    (B) False

  5. The activation energy is the minimum amount of energy required to start a chemical reaction.
    (A) True
    (B) False

  6. The rate of a chemical reaction is affected by the activation energy.
    (A) True
    (B) False

  7. The rate of a chemical reaction is inversely proportional to the activation energy.
    (A) True
    (B) False

  8. The rate of a chemical reaction is directly proportional to the temperature.
    (A) True
    (B) False

  9. The rate of a chemical reaction is directly proportional to the concentration of the reactants.
    (A) True
    (B) False

  10. The rate of a chemical reaction is directly proportional to the surface area of the reactants.
    (A) True
    (B) False

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