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Showing posts with the label Cooling by adiabatic demagnetization

Depression in Freezing point and Elevation in Boiling point

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Depression in Freezing Point: Depression in freezing point means freezing point of solution is always less than that of its pure solvent due to lowering of vapour pressure of solution. Depression in freezing point have the formula as given below, ∆T f = i × K f × m                                       eq.. (1) K f = cryoscopic constant This equation tells us that depression of freezing point depends only on   molality of solutions, so it is a colligative property. m= 1000W 2 /W 1 ×M 2                           putting the value of molality in we get          ∆T f   = i × K f × 1000W 2 /W 1 ×M 2        ...
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Adiabatic Demagnetization

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  What is the process of Adiabatic Demagnetization? How cooling takes place by Adiabatic Demagnetization? Cooling by Adiabatic Demagnetization: According to 3 rd law of thermodynamics, entropy of a substance decreases with decrease in temperature and ultimately becomes zero at absolute zero for a perfect crystalline solid. In 1926 William Francis Giauque and Peter Debye independently suggested that adiabatic demagnetization would provide a practical way to reach extremely low temperatures. Seven years later having overcome technical problems Giauque cooled gadolinium sulfate to 0.25K a new record for temperatures. To understand how he achieved this, the graph between entropy and temperature for low and high values of magnetic field provides essential information. This graph shows entropy of paramagnetic substance as a function of temperature in the presence and absence of applied magnetic field. The curves x and y   are S-T diagrams in the absence and presence of a...
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Balancing Redox Reactions by Ion-Electron method(part1)

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  How to balance redox reactions? How can we balance redox reactions by Ion-Electron method? Balancing redox reactions: The balancing of redox equations by the loss and gain of electrons, usually involves quite a few ions, which do not undergo change in valence and which are not necessary for the process of balancing. The ion –electron method eliminates a unnecessary ions and retains only those, which are essential. Following are the general rules for balancing redox equations by ion- electron method. 1.    Assign oxidation states to determine species being oxidized and reduced, and write the half reactions. 2.    Balance each half reaction. a.    Balance the atoms being oxidized or reduced. b.    Balance oxidation number by adding electrons. c.    Balance the other elements that are present, for example S with SO 4 2- or Cl with Cl 1- . d.    Balance oxygen atoms by adding H 2 O. e.    Balan...
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Paramagnetic, Diamagnetic, Ferromagnetic, Antiferromagnetic and Ferrimagnetic behavior of substances

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What is Paramagnetic, Diamagnetic, Ferromagnetic, Antiferromagnetic and Ferrimagnetic behavior of substances? What is the effect of temperature on these properties? Paramagnetic substances: These substances are attracted by the magnetic field and have unpaired electrons. These lose magnetism in the absence of magnetic field. Some examples of paramagnetic substances are transition metals like Cr, Mn, Co, Fe and metal oxides like CuO,VO 2 . Diamagnetic substances: These substances are weakly repelled by magnetic field and have no unpaired electrons. Some examples of diamagnetic substances are H 2 O, benzene, NaCl, TiO 2 . Ferromagnetic substances: Such substances are strongly attracted by magnetic field. In the absence of magnetic field magnetic field these substances have magnetic domains randomly oriented in such a way that their overall magnetic moment gets cancelled. But in the presence of magnetic field they are oriented in such a way that they together produce a str...
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Slater's Rule

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         What is Slater's Rule and its significance? How to calculate value of σ  and Zeff using Slater' Rule: Slater's Rule : Slater’s rules are a set of empirical guidelines used to calculate the shielding constant (σ) and the effective nuclear charge (Zeff) experienced by an electron in a multi-electron atom. They were introduced by John C. Slater to simplify the complex quantum mechanical interactions between electrons. These rules estimate how much the inner electrons reduce the attractive force of the nucleus on outer electrons. Mathematically:                              Zeff=Z−S where: Z = atomic number (total nuclear charge)             S = shielding constant (calculated using Slater’s rules Significance of Slater's Rule: To quanti...
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