ENERGY KIDS

Energy transformation - Chemical energy


Chemical energy is one of the 7 main form of the energy. Chemical energy is a potential energy. That type of energy comes from the bonds of atoms and molecules.

Chemical energy as a heat is possible to be released during a chemical reaction. The chemists called it an exothermic reaction.
Some of the reactions require an input of heat to proceed. During such a reaction that energy can be stored as chemical energy in newly formed bonds.
Food also consist chemical energy that the body convert into mechanical energy and heat.

Chemical reactions
Chemical reactions are everywhere around us. When you mom is cooking is a chemical reaction between different ingredients and products. When your dad is driving a car is also type of chemical energy.

Photosynthesis is also a chemical reaction. This is a process where the plants using light energy from the sun convert carbon dioxide and water to glucose sugar and oxygen gas through a series of reactions.


Chemical reactions can be placed in the following categories:
  • Combustion
  • Synthesis
  • Single displacement
  • Decomposition
  • Double displacement
  • Acid-base

Combustion
During this reaction the oxygen combines with another compound to form water and carbon dioxide. This type of reactions produce heat - exothermic reaction.
An example - burning of napthalene:

C10H8 + 12 O2 --> 10 CO2 + 4 H2O


Synthesis
When two or more simple compounds combine to form a more complicated one.
Example is the combination of iron and sulfur to form iron sulfide:

8 Fe + S8 --> 8 FeS


Decomposition
This is the opposite of a synthesis reaction. During the decomposition reaction a complex molecule breaks down to make simpler ones. In other words one compound decomposes (splits-up) into two or more compounds and/or elements. Most decomposition reactions are endothermic.

Examples
The process of electrolysis of water into oxygen and hydrogen gas:
2 H2O --> 2 H2 + O2

Process of decomposition of potassium chloride into potassium and chlorine gas:
2 KCl(s) → 2 K(s) + Cl2(g)


Single displacement (substitution)
When one element trades places with another element in a compound.

Examples
Process when zinc combines with hydrochloric acid. The zinc replaces the hydrogen:
Zn + 2 HCl --> ZnCl2 + H2

When hydrogen react with magnesium the hydrogen is replaced/displaced by magnesium:
Mg + HCl --> MgCl2 + H2

Double displacement
When the anions and cations of two different molecules switch places, forming two entirely different compounds.

Equation is expressed as:
The equation is expressed in general as :
AB + CD --> AC + BD

Aqueous barium chloride reacts with sulfuric acid to form solid barium sulfate and hydrochloric acid:
BaCl 2 ( aq ) + H 2 SO 4 ( aq ) → BaSO 4 ( s ) + 2HCl ( aq )

Acid-base
This is a type of double displacement reaction that takes place when an acid and base react with each other.

Examples
The most fundamental acid-base reaction is the dissociation of water: H2O --> H+ + OH-