Химия. Экология. Медицина



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VANT HOFF

Moh Hayek, group 3. Scientific adviser is Tatyana Tishakova.


The Van't Hoff equation is based on the assumption that the enthalpy and entropy are constant with temperature changes. In practice, the equation is experimentally approximate in that both enthalpy and entropy changes of a process (reaction) vary (each differently) with temperature. Its accuracy is determined in accounting for the curvature in the standard enthalpy changes over temperature. A major use of the equation is to estimate a new equilibrium constant at a new absolute temperature assuming a constant standard enthalpy change over the temperature range.

Under standard conditions, the van't Hoff equation is




where R - is the gas constant. This canal so be written as


Taking the definite integral of this differential equation between temperatures T1 and T2 gives


In this equation K1 is the equilibrium constant at absolute temperature T1, and K2 is the equilibrium constant at absolute temperature T2.

From the definition of Gibbs free energy




where S is the entropy of the system, and from the Gibbs free energy isotherm equation


the linear form of the van't Hoff equation can be obtained

Therefore, when the range in temperature is small enough that the standard enthalpy change is essentially constant, a plot of the natural logarithm of the equilibrium constant versus the reciprocal temperature gives a straight line. The slope of the line is equal to minus the standard enthalpy change divided by the gas constant, -ΔHo/R, and the intercept is equal to the standard entropy change divided by the gas constant, ΔSo/R. Differentiation of this expression with respect to the variable (1/T) yields the van't Hoff equation.

When solute particles associate in solution, is less than 1. For example, carboxylic acids such as ethanoic acid (acetic acid) orbenzoic acid form dimers in benzene, so that the number of solute particles is half the number of acid molecules.

When solute particles dissociate in solution, is greater than 1. (e.g. sodium chloride in water, potassium chloride in water,magnesium chloride in water)

When solute particles neither dissociate nor associate in solution, equals 1. (e.g. Glucoseinwater)

The value of the actual number of particles in solution after dissociation ÷ the number of formula units initially dissolved in solution. Means the number of particles per formula unit of the solute when a solution is dilute.

AssociationofMolecules (i<1)



EXTRACTION OF IRON

Ashiq Parapill, group 4. Scientific adviser is Evgenia Grabovetskaya.


Iron ores are rocksand minerals fromwhich metallic iron can be economically extracted.The iron itself is usually found in the form of magnetite {Fe3O4}, hematite {Fe2О3}, or siderite {FeСО3}.

It is extracted by a process of smelting. Iron ore consists of oxygen and iron atoms bonded together into molecules.to convert it to metallic iron it must be smelted or sent through a direct reduction process to remove the oxygen.it consists of following steps.

• Air blast and charcoal {coke}: 2C +O2 →2CО

• Carbon monoxide (СО) is the principal reduction agent.

• Stage one : 3 Fe2О3 + CО → 2 Fe3О4 + CО2

• Stage two: Fe3О4 +CО→ 3FeО + CО2

• Stage three : FeО + CО →Fe +CО2

• Limestone calcining : CaCO3 → CaO + CО2

• Lime acting as flux : CaO + SiO2 → CaSiO3

Iron ore is basic raw material used for iron and steel making industry .steel is used in construction,aircrafts, automobiles etc...

The iron obtained contains 4% carbon and many impurities like S,P,Si.This is known as pig iron.This is changed to cast iron.cast iron has slightly lower carbon content and is extremely hard and brittle.They further reduced to form wrought iron and it is the purest form of commercial iron and is prepared from cast iron by oxidising impurities in a reverberatory furnace lined with hematite.This hematite oxidises carbon to carbon monoxide.Cast iron is used for making casting stoves,gutter pipes,toys,etc.Wrought iron is used in making anchors,wires,bolts,chains and agricultural implements.

DOROTHY HODGKIN: A GREAT CHEMIST

Morenike Ademola, group 5. Scientific adviser is Evgenia Grabovetskaya.


In my opinion, women are not getting enough credit for their outstanding work in science. We always hear of male scientists such as Albert Einstein and Stephen Hawking, but never about women like,Lise Meitner and Ada Yonath, who made important contributions to their respective fields in the same era. This is why I decided to write about a great female chemist, whose work made an outstanding impact on both scientific and medical fields, Dorothy Hodgkin.

British chemist, Dorothy Mary Hodgkin (12 May 1910-29 July 1994), nee Crowfoot, was born in Cairo, where her father worked with the Egyptian Education Service, and lived there for the next four years, before returning to England. At the age of ten, Dorothy went to Sudan visit her expatriate parents and she met Dr. A. F. Joseph, who encouraged her interest in the world of chemicals and crystals. From 1921 to 1928, she attended the Sir John Leman School, where only she and one other girl were allowed to join the boys for chemistry. Dorothy went to Oxford and Somerville College from 1928 to 1932, and there she studied chemistry and biochemistry, and took part in a crystallography course. She earned her PhD at the University of Cambridge.

Dorothy Hodgkin most notable works are her discovery of the structures of Vitamin B12, Insulin and the famous antibiotic penicillin with the help of X ray crystallography. Even though many bacterial strains are now resistant to penicillin antibiotics, they are historically significant because they are the first drugs that were effective against many previously serious diseases, such as syphilis, and infections caused by staphylococci and streptococci.And the drug is responsible for saving more than a million lives in the 20th century.

Her discovery of the structures has made it possible for these complex biological molecules to be manufactured and distributed all around the world, thus saving thousands of lives everyday.



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