Laws Of Thermodynamics

Thermodynamics is the branch of science which deals with the study of the flow of heat or any other forms of energy into or out of a system as it undergoes a physical or chemical change. The study of thermodynamics is based on three important laws or generalisations which is confirmed by well established experimental results. These laws are known as the Zeorth, First, Second and Third Laws of Thermodynamics.

Zeroth Law of Thermodynamics states that :  ''If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other.''    

A system is said to be in thermal equilibrium when it experiences no net change in thermal energy. If A, B, and C are distinct thermodynamic systems, the zeroth law of thermodynamics can be expressed as:

• "If A and C are each in thermal equilibrium with B, A is also in equilibrium with C."

 

The zeroth law was not initially recognized as a law, as its basis in thermodynamical equilibrium was implied in the other laws.  Once the importance of the zeroth law for the definition of temperature was realized, it was impracticable to renumber the other laws, hence it was numbered the zeroth law. 

 

First law of thermodynamics states that : A change in the internal energy of a closed thermodynamic system is equal to the difference between the heat supplied to the system and the amount of work done by the system on its surroundings.  E = q - W

The first law is in fact, an application of the principle known as the Law of Conservation of Energy to thermodynamic systems. Other statements of the first law are:

1. The total energy of an isolated system remains constant though it may change from one form to another.

2. Energy can neither be created nor destroyed, although it can be changed from one form to another.

3. Total energy of a system and surroundings remains constant.

4. It is not possible to construct a perpetual motion machine, i.e., a machine which can produce work without expenditure of of energy.


Second law of thermodynamics states that : ''Heat cannot spontaneously flow from a colder location to a hotter location.''

The need for the second law arise from the fact that for a particular process or change, the first law helps us to balance the internal energy, heat released and work done on the system or by the system. But, it does not sy anything about the thermodynamic possibility of the process to occur.

The second law explains that ''whenever a spontaneous or irreversible process takes place, it is accompanied by an increase in the total entropy of the universe.'' All spontaneous processes take place in the direction of increasing entropy. Entropy is a state quantity that is a measure of the randomness or disorder of the molecules of the system.

Third law of thermodynamics states that : As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

The third law does not give any any new concept. It only places a limitation to the value of entropy of a crystalline solid. The entropy of a substance varies directly with temperature. If we increase the temperature of a system, for example water, the molecules attain kinetic energy and starts moving restlessly resulting in an increasing entropy of the system. But, if we cool the system, the vibration of molecules slow down limiting the freedom of movement thereby decreasing the entropy. Finally, at absolute zero all molecular vibrations ceases resulting in nil disorder and the entropy of the system will be zero. i.e., S=0 at T=0K.

 

Hydrogen Energy

INTRODUCTION

Hydrogen is the simplest element known to exist having one proton and one electron. It has the highest energy content of any common fuel by weight, but the lowest energy content by volume. It is the lightest element and a gas at normal temperature and pressure. It is also the most abundant gas in the universe, and the source of all the energy we receive from the sun through the process of nuclear fusion. Hydrogen is always present in the compound form in combination with elements like oxygen (H2O), carbon (CH4), etc. It is one of the most abundant elements on the earth’s crust.

Hydrogen is one of the most promising energy carriers in future. It is a high efficiency, low polluting fuel that can be used for transportation, heating, and power generation in places where it is difficult to use electricity. Hydrogen was observed and collected long before it was recognized as a unique gas by Robert Boyle in 1671, who dissolved iron in diluted hydrochloric acid. 

HYDROGEN PRODUCTION AND BENEFITS

Since molecular hydrogen does not occur abundantly on earth’s atmosphere, it must be manufactured. There are several ways for producing hydrogen for commercial purposes. Hydrogen can be produced using diverse, domestic resources including fossil fuels, such as coal and natural gas; nuclear; and biomass and other renewable energy technologies, such as wind, solar, geothermal, and hydroelectric power. Some methods for hydrogen production are natural gas reforming, renewable electrolysis, photo electrochemical processes, high temperature thermochemical water splitting etc many of which are only in the early stages of development. Hydrogen can generate power without exhaust emission in fuel cells. Environmental benefits and health benefits are even greater when hydrogen is produced from low or zero-emission sources such as solar energy, wind and and nuclear energy. Hydrogen combustion produces only water as the by-product. It can also compensate for the intermittency of renewable energy production.

FOOD ADDITIVES

Food additives are substances added to food to preserve their freshness, improve their visual appeal or taste, enhance their flavor etc. Humans have been using food additives since long time. For example, preserving food by adding vinegar, oil, sugar and salt. Since more number of food additives, both artificial and natural ones, have been introduced with the advent of processed food, it is important to know the type of chemicals used as food additives.

There are various types of food additives used with different purposes. Some of them are :-

Food Acids:  Added in order to add tartness to the flavor of foods, also act as anti-oxidants and preservatives. Example:- citric acid, lactic acid, fumaric acid, malic acid, tartaric acid, phosphoric acid (in colas), and vinegar. 

Food coloring: Colorings are added to food to replace colors lost during preparation, or to make food look more attractive. Example:- Caramel coloring (E150), made from caramelized sugar. The great bulk of artificial colorings used in food are synthetic dyes.

Flavors: These are added in order to enhance the flavors of foods, which can be either artificial or made from natural sources. Some of the common flavoring agents are monosodium glutamate (MSG), maltol, and disodium guanylate. Some of the compounds used to produce artificial flavors are;

Chemical	Odor
Ethylvanillin	Vanilla
Isoamyl acetate	Banana
Benzaldehyde	Bitter almond
Cinnamic aldehyde	Cinnamon
Ethyl propionate	Fruity
Methyl anthranilate	Grape
Limonene	Orange

Preservatives: These are chemicals that are added to food products in order to prevent food from spoiling due to the growth of micro-organisms like bacteria and fungi. Apart from being anti-microbial, there are also preservatives that are anti-oxidants. Common antimicrobial preservatives include calcium propionate, sodium nitrate, sodium nitrite, sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) and disodium EDTA. Antioxidants include BHA and BHT. 

Sodium nitrite and sodium nitrate are two closely related chemicals used for centuries to preserve meat. Nitrate is harmless but, it is readily converted to nitrite where it can form nitrosamines, extremely powerful cancer-causing chemicals. The chemical reaction occurs most readily at the high temperatures of frying. Nitrite has long been suspected as being a cause of stomach cancer. 

Antioxidants: Antioxidants such as vitamin C act as preservatives by inhibiting the effects of oxygen on food or preventing them from becoming rancid, and can be beneficial to health.

 

Stabilizers: Stabilizers, thickeners and gelling agents, like agar or pectin (used in jam) give foods a firmer texture.

Emulsifiers: These are added in order to enable oils and water to emulsify, or remain combined together, such as homogenized milk, mayonnaise, and ice-cream. Examples of food emulsifiers are egg yolk where the main emulsifying agent is lecithin, honey, and mustard, where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers.

There has been significant controversy associated with the risks and benefits of food additives. Some artificial food additives have been linked with cancer, digestive problems, neurological conditions, ADHD, heart disease or obesity. Natural additives may be similarly harmful or be the cause of allergic reactions in certain individuals.To regulate these additives, and inform consumers, each additive is assigned a unique number, termed as "E numbers", which is used in Europe for all approved additives.

Associative and Dissociative Substitution

Associative substitution describes a pathway by which coordination and organometallic complexes interchange ligands. Associative mechanism resembles the SN2 mechanism in organic chemistry. The opposite pathway is dissociative substitution, being analogous to SN1 pathway. Intermediate pathways exist between the pure associative and pure dissociative pathways, these are called interchange mechanisms.


Associative mechanism

• Metal size should be large
• Ligand size should be small
• Incoming group should have pi bonding ability (CN- is a pi acid ligand)
• Rate depend on the nature of nucleophile
• Trigonal bipyramidal intermediate 

    L5MX + Y =   L5MXY        (SLOW)
    L5MXY =    L5MY + X        (FAST)

    Rate = k [L5MX] [Y]
 

Dissociative mechanism

• Metal size should be small
• Ligand size should be large
• Rate does not depend on nature of the nucleophile

    L5MX =  L5M + X   (SLOW)
    L5M + Y =  L5MY   (FAST)

    Rate = k [L5MX]

Zinc Oxide Nanomaterials

Zinc oxide is one of the most important II-VI semiconductor material with direct wide band gap (3.37 eV or 375 nm), good transparency, high electron mobility (>100 cm2/Vs) photoconductivity, strong room-temperature luminescence large exciton and biexciton energies of 60 meV and 15 meV respectively. It has attracted increasing attention due to its excellent optical and electrical properties, inexpensiveness, relative abundance, chemical stability towards air, ability to produce significant quantum confinement effect. 

Since ZnO is an important trace element for humans, it is environment friendly and suitable for in vivo applications. Zinc oxide has high refractive index, high thermal conductivity, antibacterial and UV-protection properties. Consequently, it is added in various materials and products including plastics, ceramics, glass, cement, rubber, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants etc. and non-toxicity, making it a suitable additive for textiles and surfaces that come in contact with humans.

Nanosized ZnO has immense importance due to its multifunctionality. Thermal stability, irradiation resistance and flexibility to form different nanostructures are the advantages that highlight its promising applications in solar cells and electronic devices, ultraviolet-light detectors and photo diodes and in catalysis.Structures like nanowires, nanobelts and nanorings are of great interest in photonics research, optoelectronics, nanotechnology, and biomedicine. Therefore, the controlled synthesis of various ZnO nanostructures such as nanocrystals, nanowires, nanobelts and other complex nano architectures has been extensively explored.

Zinc oxide nanostructure growth is heavily researched presently. The substance is likely to have the largest variety of nanostructures (and their associated properties) among all known materials. Its hexagonal lattice can easily match catalyst lattice structure and facilitate controlled growth patterns. Positive zinc surfaces and negative oxygen surfaces create electric dipoles that facilitate polarization growth along certain directions and planes under applied voltage and temperature. Different techniques such as sol-gel, spray pyrolysis, thermal evaporation, wet chemical processes etc are used for the synthesis of ZnO nanomaterials.

ZnO quantum dots exhibit emission bands in the ultraviolet and visible regions as shown by its photoluminescence spectra. The UV emission band at around 370 nm is usually attributed to the interband transition or the exciton combination in ZnO . Even though the emissions in the visible region are associated with the electronic defects due to surface states or trapping effects in the QDs, there are still
controversies related to the unambiguous electron transitions. In the visible region, the blue emission in ZnO QDs has considerable importance in biological fluorescence labeling. Several studies indicate that ZnO is one of the most efficient oxide-based phosphors in both photoluminescence (PL) and electroluminescence (EL).

Considerable studies have been done on the properties of metal incorporated fluorescent materials like Co, Ni and Fe doped ZnO aiming to develop efficient magnetic semiconductors. The properties of inner-transition metal doped ZnO nanoparticles have also been subjected to tremendous amount of studies. The combination of magnetic and optical properties provides the composites significantly important applications in biomedical fields including drug targeting, bioseparation and diagnostic analysis.

ENDOSULFAN

Endosulfan is an organochlorine insecticide and acaricide with a cyclodiene sub-group. It is highly toxic and can  bioaccumulate in organisms. It can also act as an endocrine disruptor i.e., it interferes with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis (normal cell metabolism), reproduction, development, and behavior.

Endosulfan has been used in agriculture around the world to control insect pests including whiteflys, aphids, leafhoppers, Colorado potato beetles and cabbage worms. Because of its non-specificity it impacts many beneficial insects also. It is also used as a wood preservative.

Comercial names : Beosit, Thiodan, Cyclodan, Malix, Thifor, Endocide etc.

Specifically, it is produced by the Diels-Alder reaction of hexachlorocyclopentadiene with cis-butene-1,4-diol and subsequent reaction of the adduct with thionyl chloride.Technical endosulfan is a 7:3 mixture of stereoisomers, designated α and β. α- and β-endosulfan are conformational isomers arising from the pyramidal stereochemistry of sulfur. α-Endosulfan is the more thermodynamically stable of the two, thus β-endosulfan irreversibly converts to the α form, although the conversion is slow.

Endosulfan breaks down into endosulfan sulfate and endosulfan diol, both of which, according to the EPA, have "structures similar to the parent compound and are also of toxicological concern. Since it neither  dissolves in water easily nor stick to soil particles readily, its transport to other regions is easier.

India the world's largest user of endosulfan, and a major producer with three companies—Excel Crop Care, H.I.L., and Coromandal Fertilizers—producing 4,500 tonnes annually for domestic use and another 4,000 tonnes for export.


In 2001, in Kerala, India, endosulfan spraying became suspect when linked to a series of abnormalities noted in local children. Initially endosulfan was banned, yet under pressure from the pesticide industry this ban was largely revoked.

Endosulfan is acutely neurotoxic to both insects and mammals, including humans.  Symptoms of acute poisoning include hyperactivity, tremors, convulsions, lack of coordination, staggering, difficulty breathing, nausea and vomiting, diarrhea, and in severe cases, unconsciousness. Doses as low as 35 mg/kg have been documented to cause death in humans, and many cases of sub-lethal poisoning have resulted in permanent brain damage. Farm workers with chronic endosulfan exposure are at risk of rashes and skin irritation.

Quantum tunnelling

Quantum tunnelling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount because its total mechanical energy is lower than the potential energy of the barrier.

Quantum tunnelling is where a particle is found outside a confining potential despite it having insufficient energy to cross the barrier classically. 

Particles are confined to certain regions of space because they do not have enough energy to escape from that region. These regions are defined by potential energy curves.

The effect arises from the fact that a wavefunction does not fall abruptly to zero at the walls of a container (unless the potential is infinite), but decays exponentially inside the barrier. The result of this is that the wavefunction may be non-zero on the far side of the potential barrier and hence, by the Born interpretation of the wavefunction, there is some probability of finding the particle there. 

Quantum tunnelling occurs on an extremely small scale. We cannot directly perceive what a particle does when it tunnels so much of our understanding of the process is shaped by the language and imagery of the macroscopic world.

Quantum Tunneling has a number of applications like, it is used to explain the Alpha Decay of the Uranium Nucleus, it is used in fabricating high speed transistors and new age cooling equipments.