Understanding Chemical Reactions

Watch video: Structure of atom and how is light emitted? (http://www.youtube.com/watch?v=XVZSD23mD1Q) 

.Important notes on chemical reactions (for a quick reference)

1) All fusion chemical reactions are exothermic. I.e. Overlapping between atomic shells of two or more atoms release energy in the reaction. 

2) All fission chemical reactions are endothermic. I.e. detaching between atomic shells of two or more atoms absorbs energy in the reaction.

3) Mass loss in an exothermic chemical reaction is due to the releasing (explosion) of space matter, that present in the atomic shells of the reactant atoms (see Structure of an atom) to the outer world, when they overlap each other.  

4) Mass gain in an endothermic chemical reaction is due to the absorption (implosion) of space matter from outside of the reactant atoms to their shells when the reactant atoms detach each other. I.e. when the reactant atoms are detach each other, the space matter will enter to the atomic shells 

from outside for maintaining the space matter densities in natural level in the shells and for this bond braking reactions, the reactant atoms absorb energy (see chemical energy).

The below diagrams show the space matter shells in atoms and what will be happened when a bond making occurs between atoms.

Hydrogen atom	Hydrogen atom (diameter)	Hydrogen- Hydrogen bond
Nitrogen molecule (single bond)	Nitrogen molecule(triple bond)	Oxygen atom

Abstract

A free atom (without any binding) of an element has its own 'natural volume' in a constant temperature and pressure. But, when atoms react with other atoms (bonding- metallic or ionic or covalent bonding), the volume of individual atoms decrease because of the overlapping between them. I.e. the volume of any product molecule is less than the sum of the separate volumes of its reactant atoms. The releasing of heat energy (or any other form of energy) in a chemical reaction is directly related to the 'how much the atoms (atomic shells) are overlapping each other'. If the overlapping is more, then the releasing of energy will be also more and if the overlapping is less, then the releasing of energy will be also less. From these facts, we can differentiate the exothermic chemical reactions and endothermic chemical reactions in a different way. 

a) If the net volume of the product or products (in any type of reactions) molecules are lesser than the net volume of the reactants, then it will be an exothermic reaction. 

For example: 

1). Reaction between hydrogen and oxygen that produces water molecule. 2H₂+O₂ --> 2H₂O

 2) Methane, or natural gas (CH₄), burns in oxygen (O₂) to form carbon dioxide (CO₂) and water (H₂O)

In both of the above exothermic reactions, the net volume of the product molecules is lesser than the volume of reactant molecules (also, the net mass of the product molecules are slightly less than the reactants).

b) If the net volume of the product or products molecules (in any type of reactions) is greater than the net volume of the reactants, then it will be an endothermic reaction.

For examples: 

1) Electrolysis of water molecules into hydrogen and oxygen.

2) Electrolysis of salt copper chloride into copper cations and chloride anions.
    CuCl₂ --> Cu₂⁺ + 2Cl ^-

In both of the above endothermic reactions, the net volume of the product molecules is greater than the volume of reactant molecules (also, the net mass of the product molecules are slightly greater than the reactants).

We can see that one of the major products of most of the exothermic chemical reactions are water molecules. The major products in the combustion of hydrocarbon molecules are carbon dioxide, carbon monoxide etc along with the water molecules. One another important fact is that, the chemical bonding force (chemical binding energy) of atoms in water molecules or carbon dioxide molecules are much stronger than that of other ordinary molecules. Interestingly, most of the chemical reactions that produce water molecules or carbon dioxide molecules are highly exothermic.

TNT Molecule

Molecular structure of trinitrotoluene - a powerful explosive

The molecule consists of carbon, hydrogen, oxygen, and nitrogen atoms, TNT molecule collapses when it jolted, and that enables the oxygen atoms to react with the carbon and hydrogen atoms, producing carbon dioxide and water molecules, respectively. The breakdown also releases the nitrogen atoms, which then form nitrogen gas.

In a TNT molecule, the hydrogen, oxygen, carbon and nitrogen atoms are bonded in very weakly. I.e. the highly combustible atoms are arranged in very close together in the molecule. A small amount of heat energy (vibration) results the atoms in the molecule set them free (it is an endothermic reaction) and since the distance between these atoms is in atomic scales (in angstroms units) they will react (bond) immediately with the help of the above stated small amount of heat. Since the decreasing of volume in the molecular formation of CO₂, H₂O and Nitrogen (also the missing mass) are much greater than any other ordinary chemical reactions as stated above, the releasing and the explosion of space matter will be also much greater. Because of this space matter explosions are taking place where from the regions that the carbon & oxygen, hydrogen & oxygen and nitrogen atoms are bond together, the product molecules act as projectiles with tremendous kinetic energy. When these highly energetic molecules collide with the surrounding atoms/ molecules cause the generation of huge amount of thermal energy and that eventually causes the production of a super heated gas mixture of Nitrogen, carbon dioxide, water vapor etc.

Releasing of energy in a chemical reaction is proportionate with how much the space matter is released in the chemical bonding (overlapping between atomic shells) and which of the shells are involved in the reactions. When two atoms are bonded together, the releasing of energy can be calculated with considering of the parameters of the space matter densities of the overlapped shells of the atoms and the total volume that decreased in the molecular formation.

calculation