Fcc unit cell

Introduction to unit cell
A regular three dimensional arrangement of points in space is called a crystal lattice. A unit cell is the smallest of a crystal lattice which, when repeated in different directions generates the entire lattice

Face centered cubic unit cell

A face centered cubic unit cell contains atoms at all the corners and at the centre of all the faces of the cube. Each atom located at the face centre is shared between two adjacent unit cells and only half of each atom belongs to a unit cell. Thus, in a face centered cubic unit cell:

1. 8 corners atoms × 1/8 atoms per unit cell=1 atom
2. 6 face centered atoms × 1/2 atoms per cell=3 atoms

Therefore, total no. of atoms per unit cell = 4 atoms

Packing efficiency of fcc unit cell

Packing efficiency is the percentage of total space filled by the particles. Let us calculate the packing efficiency of fcc unit cell. Let the unit cell edge be ‘a’  and face diagonal be ‘b’.
We know that b=√2a
If r is the radius of the sphere, we find
    b = 4r =√2a or a = 2√2r
we know that each unit cell in fcc structure, has effectively 4 spheres. Total volume of four spheres is equal to 4×(4/3)πr³ and the volume of the cube is a³ or (2√2r)³.
Therefore,
Packing efficiency of fcc unit cell
=volume of 4 spheres ×100/volume of unit cell  %
=4×(4/3)πr³×100/(2√2r)³
=74%

Density of unit cell

Volume of unit cell = a³
Mass of the unit cell =number of atoms in unit cell×mass of each atom
=z × m
Where z is the number of atoms in unit cell and m is the mass of single atom.
Mass of an atom present in a unit cell:
    m = M/N_a   (M is molar mass)
therefore, density of the unit cell =mass/volume
         =z×m/a³ = z×M/a³×N_a
     d   =    zM/a³N_a

Summay

The number of atoms in a fcc unit cell is four and these are present at all corners as well as at the centre of all faces of the cube

Make a fuel cell

Introduction :
A Fuel Cell is a device that converts the energy of the chemical reaction between a fuel and an oxidant into electricity and heat.  It is easy to make a fuel cell working, by using an anode, cathode, catalysts and most often an electrolyte.  Fuels and oxidants are also necessary to make a fuel cell.  Fuel cells are combined into groups to obtain a usable voltage and power output, called stacks. Fuel cells generate electricity electrochemically, rather than mechanically, so they are more efficient over a wider load factor and can cut greenhouse gases by over 50 percent.  Fuel cells are very much different from batteries. Fuel cells consume reactant from an external source, which must be replenished.  Fuel cells produce electricity with an efficiency of about 70 % compared to thermal plants whose efficiency is about 40%.

How to make a fuel cell

We can make a fuel cell (Hydrogen Fuel Cell) in our kitchen in just 10 minutes, and demonstrate how hydrogen and oxygen combines to give clean electricity.
To make a fuel cell, we would need:

• One foot of platinum coated nickel wire along with small piece of wood or Popsicle stick.  
• A 9 volt battery clip and a 9 Volt battery.
• A little transparent sticky tape.
• One glass full of water.
• Volt meter device.

Hydrogen-oxygen Fuel cell

One of the most successful fuel cells uses the reaction of hydrogen as fuel and oxygen as oxidant to form water (Hydrogen oxygen fuel cell).  The cell was used for providing electrical power in the Apollo space programme.  The water vapors produced during the reaction were condensed and added to the drinking water supply for the astronauts.  In the cell, hydrogen and oxygen are bubbled through porous carbon electrodes into concentrated aqueous solutions of sodium hydroxide.  Catalysts like finely divided platinum or palladium metal are incorporated into the electrodes for increasing the rate of electrode reactions.

Catalysis plays a very important role in Hydrogen oxygen fuel cells, separating the electrons and protons of the reactant fuel (at the anode), and forcing the electrons to travel though a circuit, generating electrical power.  At the cathode, another catalytic process takes the electrons back, combining them with the protons, which have traveled across the electrolyte and the oxidant to form waste products like carbon dioxide and water.
The electrode reactions of Hydrogen oxygen fuel cell are given below:
Cathode reaction:     O₂ (g) + 2H₂O (l) + 4e⁺    4OH^–(aq)
Anode reactions:       2H₂ (g) + 4OH^–(aq)  4H₂O (l) + 4e^–
Overall reactions:     2H₂ (g) + O₂ (g)   2 H₂O (l)
The cell can run continuously as long as the reactants are supplied.

Alcohol fuel cell

Introduction

A fuel cell is an electrochemical device which converts the chemical energy of compounds into electrical energy via electrochemical reactions. Unlike a conventional battery, a fuel cell is not an energy-storing apparatus but reactants are continuously replenished into the cell separately during the operation. A Hydrogen rich compound or pure hydrogen is used as a fuel, while oxygen from the air or pure oxygen commonly serves as oxidant. The benefits obtained using a fuel cell for energy production are high efficiency and low emissions of harmfull effluents.

Alcohol fuel cell

In an alcohol fuel cell, as the name indicates alcohol is used as a fuel to produce electricity.  The cell in which Methanol is directly used as fuel is named as Direct Methanol Fuel cell. The technology behind Direct Methanol Fuel Cells (DMFC), a particular example for alcohol fuel cell.  It is still in the early stages of development, but it has been successfully demonstrated powering mobile phones and laptop computers—potential target end uses in future years.

In the early 1990s, DMFCs were not appreciated because of their low efficiency and power density, as well as other problems. Improvements in catalysts and other recent developments have increased power density to 20-fold and it is expected that the efficiency may eventually reach 40%.

DMFC is very similar to the PEMFC in that the electrolyte is a polymer and the charge carrier is the hydrogen ion (proton). However, in a DMFC, the liquid methanol (CH₃OH) is oxidized in the presence of water at the anode generating CO₂, hydrogen ions and the electrons that travel through the external circuit as the electric output of the fuel cell. The hydrogen ions travel through the electrolyte and react with oxygen from the air or pure oxygen, used as oxidant and the electrons from the external circuit to form water at the anode completing the circuit.

Cell reactions

Reaction at the Anode:      CH₃OH + H₂O => CO₂ + 6H+ + 6e^-
Reaction at the Cathode:   3/2 O₂ + 6 H⁺ + 6e^- => 3 H₂O
Overall Cell Reaction:       CH₃OH + 3/2 O₂ => CO₂ + 2 H₂O

These cells have been tested to work in a temperature range from about 50ºC-120ºC. This low operating temperature and advantage of no requirement for a fuel reformer make the DMFC an excellent candidate for very small to mid-sized applications, such as cellular phones and other consumer products, up to automobile power plants.

One of the drawbacks of this alcohol fuel cell is that the low-temperature oxidation of methanol to hydrogen ions and carbon dioxide requires a more active catalyst, which typically means a larger quantity of expensive platinum catalyst is required than in conventional PEMFCs.

One other demerit of driving the development of alcohol fuel cells is the fact that methanol is toxic. Therefore, some companies have been developing the advantageous Direct Ethanol Fuel Cell (DEFC). The performance of the DEFC is currently only about half that of the DMFC, but this gap is expected to narrow within very short time.

Diagram of atom structure

Introduction :
Atom is defined as the very small particle. The atoms are having many chemical properties of the elements. The atoms structure are having the nucleus at its center. The electrons are also present in the atom. The electron is always surrounds the nucleus part. The particles like protons and neutrons are also present in the atom.

Various particles present in the diagram of an atom structure

The atom diagram structure consists of three types of particles. They are defined below the following,
1. Protons
2. Neutrons
3. Electrons

Explanation for the various particles for the diagram of atom structure

The diagram of Structure of an Atom is shown below,
                 

Protons:
The protons present in the atom are having a positive charge. The positive charge is equal to the negative charge present in the electrons. The number of particles present in the atoms is used for the representation of the atomic number. Protons are 1836 times greater than the electrons. The proton structure is discovered by the scientist named Ernest Rutherford.

• The mass of the proton is given by 938 MeV/c² = 1.67 x 10^-27 kg.
• The charge of the3 proton is given by 1.602 x 10^-19 Coulombs.
• The diameter of the proton is given by 1.65 x 10^-15 m.

Electron:
The electrons are having the negative charges. The electrons cannot able to split into the further particles. The electrons move freely in the diagram of an atom. The electron forms the electron clouds.

• The mass of an electron present in the atom is given by 9.2095 x 10^-31 kg.
• The charge of an electron present in the atom is given by -1.602177 x 10^-19 C.
• The electron rest energy present in the atom is given by 0.511 MeV.
• The spin of an electron present in the atom is given by + `(1)/(2)` or -`(1)/(2)`

Neutron:
The charge of the neutron present in the atom is having neutral charge. The neutrons present in the atom are used to represent the isotope of the element.

• The mass of the neutron is given by 1.67492729 × 10⁻²⁷ kg.
• The charge of the neutron is given by 0.  
• The spin of the neutron is given by `(1)/(2)`

Classification of Chemical Coordination

Introduction:

A metal or coordination complex is a structure which consist of a central atom or ion which is usually a metal being bonded to a molecules or anions array. Examples are ligands and complexing agents. Within a ligand, there is an atom that is directly bonded the atom in the centre or ion, this is called the donor atom. A chelate complex can be formed by polyadenylated ligand. At least one pair of electrons is donated by the ligand to the central atom/ion.

Compounds containing a coordination complex are called coordination compounds. The central atom or ion together with all ligands forms the coordination sphere.

Coordination points to the "coordinate covalent bonds" (dipolar bonds) between the ligands and the central atom.

Classification of Chemical Coordination

Metal complexes also known as coordination compounds; they consist of all metal compounds, aside from metal vapors, plasmas, and alloys. The study of "coordination chemistry" is the study of all alkali and alkaline earth metals, transition metals, lanthanides, actinides, and metalloids. Thus, coordination chemistry is the chemistry of majority of the periodic table. Metals and metal ions only exist in the condensed phases surrounded by ligands.

The different areas of coordination chemistry are classified according to the nature of the ligands. They are:

 1) Classical (or "Werner Complexes"): Ligands in classical coordination chemistry bind to metals via their "lone pairs" of electrons residing on the main group atoms of the ligand. Typical ligands are H2O, NH3, Cl−, CN−, en−

Examples: [Co(EDTA)]−, [Co(NH₃) ₆]Cl₃, [Fe(C₂O₄) ₃]K₃

2) Organo-metallic Chemistry: Ligands which are organic (alkenes, alkynes, alkyls) as well as "organic-like" ligands are found in organo-metallic chemistry like phosphines, hydride, and CO.

Example: (C₅H₅) Fe (CO) ₂CH₃

 3) Bioinorganic Chemistry: Ligands which are provided by nature, especially including the side chains of amino acids, and many cofactors such as porphyrins.

Example: hemoglobin.

Many natural ligands are Werner complexes especially including water.

4) Cluster Chemistry: Ligands which also include other metals as ligands.

Example Ru3(CO)12

Older classifications of isomerism

In the older literature, one encounters:

1) Ionisation isomerism states that the possible isomers arise from the exchange between the outer sphere and inner sphere. In this classification, the "outer sphere ligands," may combine with the "inner sphere ligands" to produce an isomer.

 2) Solvation isomerism occurs when an inner sphere ligand is replaced by a solvent molecule. This classification is absolute because it considers solvents as being distinct from other ligands.

What are chemical indicators

Introduction 
Substance which undergo some easily detectable change (such as change of colour, precipitation, etc.) during titration and which thereby indicate the equivalence point are called Chemical indicators.

Example:  Phenolphthalein, Methyl orange, Methyl red, Starch, etc.

Main Characteristics Of Chemical Indicators

Chemical indicators possess one color in the presence of an excess of the substance to be estimated, and another in the presence of an excess of the standard solution of the reagent used and thus these substances indicate the exact end-point.  A familiar example of an indicator is litmus, which is blue in the presence of an excess of alkali and red in the presence of excess of acid.
A good chemical indicator must possess the following two essential characteristics.

1. The color change of the indicator must be clear and sharp, i.e. it must be sensitive.  Thus, it would be useless if 2 or 3 c.c. of the reagent is sufficient to bring out the color change.
2. The Ph-range over which the color change takes place must be such as to indicate when the reaction is complete.

Classification Of Chemical Indicators

All well-known indicators can be classified in two ways; either on the environment in which they are used or on the basis of the types of titrations in which they are used.  In general, an indicator may be internal or external.

1. Internal indicator: If the indicator is added to the liquid which is being titrated, it is called an Internal indicator viz. litmus solution, Phenolphthalein, potassium chromate, etc.
2. External indicator: If the indicator is used outside the vessel in which the reaction is taking place, and drops of the liquid are taken out of the reaction vessel from time to time and mixed with the indicator, it is called external indicator.

Potassium ferricyanide, the most familiar example of external indicator, is used during the titration of ferrous ions as it gives blue color with ferrous ions and a brown coloration with ferric ions and thus tells us when a ferrous solution has been completely oxidized to the ferric state.  The indicator is used as external since if it is added to the ferrous solution to start with, it would have been reacted with it.

Explosive chemical reactions

Introduction :
Chemical reactions that releases energy are known as exothermic reactions.

Case I: When the reaction proceeds slowly, released energy will be dissipated smoothly and there will be few noticeable effects other than an increase in temperature.

Case II: On the other hand, when the reaction proceeds very rapidly, the energy will not be dissipated smoothly. A huge amount of energy can be deposited into a relatively small volume of atmosphere, then manifest itself by a rapid expansion of hot gases, which in turn can create a shock wave or propel fragments outwards at high speed.
There are three primary fields of application for these chemcial explosions: propellants, explosives and pyrotechnics.

Propellants works when they create a high gas pressure for moving projectiles or rockets and for similar uses.

Explosives works when they create a disruption of solid or liquid bodies, as in construction, mining or warfare.

Pyrotechnics works when they have effects that are mainly sound and light, but include many other varied applications, mainly on a small scale.

Fireworks are used as an application for entertainment, a show of light, noise and motion.

Some more examples:

Black Powder: Black powder was invented as a pyrotechnic substance, then it was applied as a propellant in firearms, and finally used in engineering and mining. The history of black powder and firearms relates to Cannon.

Smokeless Powder: Vielle discovered how to make a propellant from cellulose nitrate in 1886. The work was started with low-nitrogen guncotton, or pyrocotton, with 11%-12% of nitrogen, and plasticized it with ether and alcohol. Pyrocotton will dissolve completely in this solvent. This gel was rolled out into sheets and then the sheets were broken up into powder, after this the powder formed into grains, and these grains, mixed with various additives to control the rate of burning, chemical properties and stability in storage, made a propellant called smokeless powder that could replace gunpowder, and was more powerful.

Aromatic Explosives: One of the first aromatic explosives was picric acid, or trinitrophenol, C6H2(NO2)3OH. This particular explosive was first prepared in 1771 by Woulfe as a dye, and was also used in medicine, long before it was first employed as an explosive in 1830. Name was so given because of it's extremely sharp or bitter taste, and also in Greek word it means pikros, "sharp." It forms pale yellow crystals of density 1.76 g/cc, melting at 122°C and exploding above 300°C. It is too sensitive to heat to be poured into shells, and must be press-loaded, meanwhile another effect of it is corrosion of metals, forming sensitive picrates. The most famous aromatic explosive is trinitrotoluene, called TNT for short. TNT is deficient in oxygen, so makes a cloud of black smoke. It is a popular bursting charge for shells and bombs, replacing picric acid after World War I.