Chemical Reaction
A process of chemical combination or decomposition in which substances undergo certain chemical change to form products.
Word Equation
A chemical reaction represented with the help of the name of the chemicals is called word equation. It is also known as formula equation. It is less informative than a chemical equation.
Example:
Carbon + Oxygen $\rightarrow$ Carbon Dioxide
Chemical Equation
A chemical reaction written using the symbols and molecular formula of the reactants and products is called chemical equation. It is more informative than a word equation.
Example:
$\text{C} + \text{O}_2 + \triangle \rightarrow \text{CO}_2$
Reversible and Irreversible Reaction
- Reversible Reaction: A chemical reaction that can be reverted back is called reversible reaction. In this type of reaction, the reactants that produce products are capable of producing the same reactants. It is temporary in nature.
- Irreversible Reaction: A chemical reaction that cannot be reverted back is called irreversible reaction. It is a permanent change and thus the products that are formed cannot be used to re-generate the reactants.
Types of Chemical Reaction
Chemical Reaction is broadly categorized into two types:
- On the basis of
- Combination Reaction
- Decomposition Reaction
- Displacement Reaction
- SIngle Displacement Reaction
- Double Displacement Reaction
- On the basis of heat
- Endothermic Reaction
- Exothermic Reaction
Combination Reaction
In this reaction, reacting atoms or ions combine together to form products. It is also known as addition or synthesis reaction.
Decomposition Reaction
In this reaction, a single larger molecules gets broken down (or split into) smaller particles. It is also known as analysis reaction.
Example:
1) Decomposition of Potassium Chrloate into Potassium Chloride and Oxygen gas on the application of heat.
$\text{2KClO}_3 \ \ \displaylines{_{\triangle} \\ \longrightarrow} \ \ 2\text{KCl + 3O}_2$
Displacement Reaction
In this reaction, the atoms or radicals of reacting atoms or molecules are exchanged in between one another to form the product.
On the basis of exchange, it is categorized into two types:
Single Displacement Reaction
In this reaction, atom or radical of only one reactant is replaced by the other reactant.
Double Displacement Reaction
In this reaction, atoms or radicals are mutually exchanged in between the reactants.
Exothermic and Endothermic Reaction
- Exothermic Reaction: A chemical reaction that evolves heat as a part of product is called exothermic reaction.
- Endothermic Reaction: A chemical reaction that absorbs heat during the chemical change is called endothermic reaction.
Balanced Chemical Equation
A chemical equation must always be balanced. By balancing a chemical reaction, it refers to equating equal number of atoms of each elements both in the product and the reactant side. It is done because mass of atoms remains conserved during chemical reaction. This is to say, the sum of masses of atoms in the products side is always equal to the sum of masses of atoms in the reactants side.
Rate of Chemical Reaction
The change of reactants into products per unit time is called rate of chemical reaction. It can be altered by changing the physical conditions.
The rate of chemical reaction can be increased by doing the following tasks:
- Use of Positive Catalyst: A catalyst can either increase or decrease the rate of chemical reaction. However, the use of a positive catalyst always increases the rate of chemical reaction.
- Increase the surface area of reacting particles: On increasing the surface area of reacting particles, the number of particles in contact increases. As a result, the reaction takes place at a larger sites. The rate of reaction increases due to increase in number of reacting atoms or ions or molecules.
- Application of heat: It is clear from endothermic reactions that application of heat increases the rate of chemical reaction. This is because it increases temperature of the reacting molecules that increases the frequency of collisions between them.
- Concentration of reactants: Generally, concentrated acids react more quickly than diluted acids. It is because higher concentration refers to higher number of reacting molecules. Therefore, increase in concetration of reactants increases the rate of chemical reaction.
- Chemical nature of reactants: Some chemical substances are more reactive than the others. Therfore, the chemical reactivity of those elements also determines the rate of chemical reaction.
Other Important Definitions
- Gram Atomic Weight: The atomic weight of an element expressed in grams is called gram atomic weight of that element. Example: gram atomic weight of hydrogen is 1 gram.
- Gram Molecular Weight: The molecular weight of a compound expressed in grams is called gram molecular weight of that compound. Example: gram molecular weight of water is 18 grams.
It can be further understood as the sum of gram atomic weight of each atom present in a compound. Example: gram molecular weight of Carbon dioxide = gram atomic weight of Carbon atom + 2 * gram atomic weight of Oxygen atom
= 12 + 2 * 16
= 48 grams - One Mole: One mole is defined as the amount of a substance containing Avogardo’s number of particles (atoms, ions, molecules or particles). Avogardo’s number is equal to 6.023*1023.