Physical Chemistry and Nuclear Physics

The Mpemba effect is the observation that warmer water sometimes freezes faster than colder water. Although the observation has been verified, there is no single scientific explanation for the effect.

The molecular collisions are perfectly elastic with no loss of energy and only redistribution of energy during collision.

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.

The cage effect in chemistry describes how properties of a molecule are affected by its surroundings. In a solvent a molecule is often more accurately described existing in a cage of solvent molecules, the so-called solvent cage. Reactions occur when a molecule occasionally jumps out and meets another molecule. Typical cage lifetime in a solvent cage is 10⁻¹¹ s .

Solids diffuse very slowly as compared to liquids and gases. Constituent particles are very closely packed in solids permitting very little space for their movement.

The ionic crystals consist of positively and negatively charged ions arranged in a regular fashion throughout the crystal. They form a network of positive and negative ions in three dimension in such a way that cations and anions occupy alternate sites. These are held together by strong electrostatic forces.

Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon.

The function of the catalyst is to alter the speed of the reaction rather than to start it.

In certain reactions, one of the product acts as a catalyst. In the initial stages the reaction is slow but as soon as the products come into existence the reaction rate increases. This type of phenomenon is known as auto-catalysis. For examples The rate of oxidation of oxalic acid by acidified potassium permanganate increases as the reaction progresses. This acceleration is due to the presence of Mn²⁺ ions which are formed during reaction. Thus Mn²⁺ ions act as auto-catalyst.

If the forces of attraction existing between adsorbate and adsorbent are Vander Waal's forces, the adsorption is called physical adsorption. This type of adsorption is also known as physisorption or Vander Waal's adsorption. It can be easily reversed by heating or decreasing the pressure.

In ordinary gas, most of the electron energy levels (n-spheres) are unfilled and the electrons are free to move . As particle density is increased electrons progressively, fill the lower energy states and additional electrons are forced to occupy states of higher energy. Degenerate gases strongly resist further compression because the electrons cannot move to lower energy levels, which are already filled. The Pauli Exclusion Principle causes this.

A supersolid is a spatially ordered material with superfluid properties. Superfluidity is a special quantum state of matter in which a substance flows with zero viscosity.

There are certain, substance which, when added to the reaction mixture, retard the reaction rate instead of increasing it. These are called negative catalyst or inhibitors and the phenomenon is known as negative catalysis. Some examples are as follows. (i) Oxidation of sodium sulphite (ii) Oxidation of benzaldehyde

Electro-osmosis is a phenomenon in which dispersion medium is allowed to move under the influence of an electrical field, whereas colloidal particles are not allowed to move. The existence of electro-osmosis has suggested that when liquid forced through a porous material or a capillary tube, a potential difference is setup between the two sides called as streaming potential. So the reverse of electro-osmosis is called streaming potential.

Fluorescence spectroscopy is a type of electromagnetic spectroscopy which analyses fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy, typically, but not necessarily, visible light.

The ordinary process of dialysis is slow. To increase the process of purification, the dialysis is carried out by applying electric field. This process is called electrodialysis. The important application of electrodialysis process in the artificial kidney machine used for the purification of blood of the patients whose kidneys have failed to work. The artificial kidney machine works on the principle of electrodialysis.

Macromolecular colloidal particles are formed when on dissolution in a suitable solvent, the macromolecules have sizes which are in the colloidal range. Naturally occurring macromolecules are starch, proteins and cellulose. Man made macromolecules are polymers such as polyethylene, nylon and polystyrene. These colloids are quite stable and resemble true solutions in many respects.

Positron emission is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron (the antimatter counterpart of an electron) and a neutrino. Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-121.

A number of metals such as silver, gold and platinum, have been obtained in colloidal state by treating the aqueous solution of their salts, with a suitable reducing agent such as formaldehyde, phenyl hydrazine, hydrogen peroxide, stannous chloride etc.

Beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. In the case of electron emission, it is referred to as beta minus while in the case of a positron emission it is referred as beta plus.In electron emission, an electron antineutrino is also emitted, while positron emission is accompanied by an electron neutrino. Beta decay is mediated by the weak force.

The speeds of the neutrons produced in the fission have to be slowed down so that they are easily captured by the fuel and the fission process can take place most effectively. This is done by surrounding the fuel rods with heavy water .The material used to slow down the neutrons (without absorbing them) is called a moderator. Graphite is also used as a moderator sometimes.

Technetium-99m is used for locating brain tumors and damaged heart cells.Technetium-99m is probably the most widely used radioisotope in medicine today; it is a decay product of molybdenum-99.

The light water reactor (LWR) is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor. There are three varieties of light water reactors- the pressurized water reactor (PWR), the boiling water reactor (BWR), and (most designs of) the supercritical water reactor (SCWR).