Types of chemical reactions

The National Weekender
TECHNOLOGY

By MICHAEL JOHN UGLO

THIS is the seventh lecture on matter in the Science in Action series. The lecture is based particularly on the types of chemical reactions. Chemical reactions are the reason for all costs and economic benefits and expenditures that affect any economy of any country. Without having a clearer understanding on the sciences of it, it will be like a blind person or people making unsound decisions that compromises the well-being of that particular society, community or an economy of a nation.

The types of chemical reactions

The types of chemical reactions known are from these areas. Firstly, it is the reaction involving transfer and acceptance of electrons from an atom of a metallic element and a non-metallic element forming chemical bonds called ionic chemical bonds. The products formed have new chemical properties from the parent elements. For instance, sodium a metal chemically combining with chlorine a poisonous gas produces the product sodium chloride which is the common table salt that can be sprinkled on food to be eaten. Also with electrons, it involves sharing of electrons between two non-metals or atoms of group four elements forming crystals such as silicon forming silicon crystals using covalent bonds. Again, the parent elements are intact while the product formed show new chemical properties from the parent elements. For example, the molecule carbon dioxide is formed from covalent bond of carbon and oxygen. Carbon is found in organic substance like woods while oxygen is a gaseous element. Now, when carbon is burned in air or burned in oxygen, it forms a covalent molecule of carbon dioxide. Carbon dioxide is needed by plants to make their food called glucose in the process called photosynthesis.
The other types of chemical reactions involve the parent elements to split into different elements. This involves nuclear reactions that includes radioactive decay and also the reactions of elementary or subatomic particles that is described in quantum field theory such as the electron captures.
In electron captures, reactions by protons in a nucleus, which will cause a proton to change to a neutron from its electron orbit. A gamma ray is emitted with a neutrino. A neutrino and a positron are emitted in a beta plus decay. This will change a neutron into a proton and this process is also known as positron emission. In a negative or minus-beta emission, the nucleus will emit an electron and an antineutrino and that will convert a neutron to a proton.
Radioactivity also known as radioactive decays or nuclear disintegration is the break-up of unstable nucleus of elements. After the break up from parent nucleus to daughter nuclides very chemically different chemical elements can be formed. These different chemical elements will have very different mass numbers which include the number of protons together with the number of neutrons. Also, different atomic numbers which include the different number of protons. For instance, uranium will decay to produce plutonium and thorium.
The increase in chemical reactions happen due to increase in temperature and concentration of the reactants. The increase in temperature causes atoms to be excited because they provide the activation energy that breaks the chemical bonds and set the atoms free to combine with other atoms. They then, increasingly collide to cause the increase in the scale of the chemical reaction.
Catalysts are chemical substances that are used in chemical reactions to speed up the reaction or slow it down but are not used up themselves. The catalysts hence, can then be used over and over again in new chemical reactions.
The kinds of chemical reactions include redox reactions, displacement (both single and double) reactions, synthesis reactions, decomposition reactions and combustion reaction. All the different reactions are represented by a chemical equation. The chemical equation specifies the kinds of reactants involved and the products produced. In giving the symbols of both the reactants and the products produced, it also specifies the number of atoms involved in both sides (reactants and products) of the equation and the numbers in front of the individual elements added to balance the equation gives the number of moles involved. The equation can be written in words called the word equation or in symbols called chemical equations. For instance;

Word equation

Hydrogen gas + Oxygen gas = Water

Chemical equation

H2 + O2 = H2O

The above equation has to be balanced and so it should be correctly written as;

Chemical equation

2H2 + O2 = 2H2O

This chemical reaction of hydrogen gas with oxygen gas produces molecules of water. So, when the equation is balanced as indicated by the twos in front of H2 and H2O as 2H2 and 2H2O it is really 2 moles of hydrogen gas with a mole of oxygen gas producing two moles of a water molecule.
There are also other chemical reactions known as complexation, Acid-Base reactions, Precipitation solid state reactions, reactions at solid and gas interface and photochemical reactions.
Common reaction involved here are Complexation, Acid-Base reactions, Precipitations, Solid state reactions, Reactions at solid and gas interface and Photochemical reactions.
Particular chemical reaction that takes place is the chemical reactions that go on in the living world are studied in organic chemistry. Organic chemistry involves the commonly known reactions such as substitutions and additions and eliminations. In substitution reactions groups of atoms acting as a unit called a functional group is replaced by another group that is electrophilic, nucleophilic or one that is a radical. It can also be replaced by a halogen of the group seven elements. In substitution reactions with electrophiles, it has an atom or a molecule that is lower in electron density therefore carry a positive charge. Therefore, it is more lenient towards a more negative substrate to replace the atom or molecule there to effect, the electrophilic chemical reaction. For instance, such electrophiles will include carbonyl groups of carbon atoms, sulfur cations as well as nitronium cations. This chemical reaction is seen in particularly aromatic hydrocarbons.
In nucleophilic chemical reactions, an atom or a molecule has a higher electron density and therefore it carries a negative charge. When it seeks a substrate of a positive charge or a neutral substrate, it replaces the atom or the molecule present and forms a new bond on the substrate. Examples of nucleophiles are amines, hydroxides and halides. The nucleophilic chemical reactions are mainly found in aliphatic hydrocarbons.
The elimination and addition are chemical opposites. In addition, chemical reaction, the substituents composed of double and triple bonds are changed from a carbon atom for the formation of a single bond. Furthermore, in elimination chemical reaction multiple bonds as double and triple bonds are formed when a suitable leaving group is eliminated.
The next chemical reaction is the biochemical reactions. In this particular chemical reaction, the enzymes which are made of proteins become the catalysts are thus organic catalysts that control the reactions. The reactions are very specific and occur inside the cells. The concentration of substrates and the temperature are very specific to the cellular environment and cannot happen outside of that environment like any other chemical reactions. That means the product of one reaction become the substrate or reactant for the next chemical reaction in a cycle of the biochemical reaction called metabolism. The other phenomenon in biochemical reactions is the production of bigger organic compounds such as proteins and carbohydrates from smaller units. This biochemical reaction is called anabolism. The energy that is used to carry out all biochemical reactions is derived from glucose. The glucose is produced from photosynthesis. All plants and animals use glucose to make a chemical compound called ATP (adenosine tri-phosphate) to carry out all reactions.
In the application of chemical reactions, these are used to make new products having the knowledge of how specific reactants combine in producing a variety of products. The amount and concentration of reagents involved together with certain temperature for activation energy to break the bonds and as well as the use of catalysts to control the rate of reaction are areas that can be used to produce new useful products.
Some specific ideas such as the acidity and alkalinity given in pH readings, emission and absorption of specific colors of radiation wavelengths as well as radioactive isotopes can be used to trace the movement of certain elements or micronutrients through an organism for study purposes.
My Prayer for PNG today is: “Trust in the Lord you shall not tire, bless you the Lord, you shall not weaken… ”

Next week: Masses, Moles and Concentrations in Science and Technology

  • Michael Uglo is the author of the textbook “Science in PNG, Pacific, Asia & Caribbean” and a lecturer in Avionics, Auto- Piloting and Aircraft Engineering. Send comments to: [email protected]