UGC-NET (NTA) Environmental Sciences, December-2019

Enthalpy, the sum of the internal energy and the product of the pressure and volume of a thermodynamic system. Enthalpy is an energy-like property or state function-it has the dimensions of energy (and is thus measured in units of joules or ergs), and its value is determined entirely by the temperature, pressure, and composition of the system and not by its history. In symbols, the enthalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system: H = E + PV.

Breeder reactors are a type of nuclear reactor which produce more fissile materials than they consume. They are designed to extend the nuclear fuel supply for the generation of electricity, and have even been mistakenly called a potential renewable energy source. An important concept for a breeder reactor is how much fissionable fuel is being produced compared to how much fuel is being used. This is known as the breeding ratio. For example for the breeding of plutonium, the ratio would be the amount of plutonium produced to the amount of uranium-235 used. In the liquid metal fast breeder reactor (LMFBR), the breeding ratio is 1.4, however the actual achieved ratio is around 1.2.

The terms net calorific value and gross calorific value of a fuel to generate motion or fuel to generate heat describe the amount of heat released in an energy source when it undergoes complete combustion with oxygen.
Net calorific value (Hᵢ) = gross calorific value (Hₛ) - condensation heat
Gross calorific value (Hₛ) = net calorific value (Hᵢ) + condensation heat
Therefore, the gross calorific value is always higher than the net calorific value.
The difference between the Gross Calorific Value and Net Calorific Value is maximum for natural gas.

Direct bandgap semiconductors (GaAs, InAs, InP, GaSb, InGaAs, GaAsSb), the photon absorption does not require assistant from lattice vibrations. The photon is absorbed and the electron is excited directly from the VB to CB without a change in its k-vector (crystal momentum hk), since photon momentum is very small.

The fate of chromium in soil is greatly dependent upon the speciation of chromium, which is a function of redox potential and the pH of the soil. In most soils, chromium will be present predominantly in the chromium (III) state. Under oxidizing conditions, chromium (VI) may be present in soil as CrO₄²⁻ and HCrO₄⁻. In deeper soil, where anaerobic conditions exist, chromium (VI) will be reduced to chromium (III) by S²⁻ and Fe²⁺ present in soil. The reduction of chromium (VI) to chromium (III) is possible in aerobic soils that contain appropriate organic energy sources to carry out the redox reaction. The reduction of chromium (VI) to chromium (III) is facilitated by low pH.

The goal of disinfection of public water supplies is the elimination of the pathogens that are responsible for waterborne diseases. The transmission of diseases such as typhoid and paratyphoid fevers, cholera, salmonellosis, and shigellosis can be controlled with treatments that substantially reduce the total number of viable microorganisms in the water. Presedimentation to remove suspended matter, coagulation with alum or other agents, and filtration reduce the organic material in the raw water and, thus, the disinfectant demand. Water, particularly surface waters, may also contain synthetic organic molecules whose demand for disinfectant will be determined by their structure. Ammonia and amines in raw water will react with chlorine to yield chloramines that do have some biocidal activity, unlike most products of these side reactions.

The chemistry of the nighttime troposphere is usually dominated by reactions of NO₃. This radical can oxidize a number of nonmethane hydrocarbons (NMHCs) and sulphur containing compounds such as dimethyl sulphide (DMS), and it also provides a route for the conversion of the oxides of nitrogen (NO. = NO + NO₂) to nitric acid (HNO₃).

Climate change, particularly global warming is said to be caused mainly by the greenhouse effect, and the resulting increase in global temperatures is causing diseases and vectors to spread to higher altitudes in mountainous regions and to higher latitudes that were previously free of the infections.
Vector-borne diseases are transmitted by arthropods including ticks and various types of mosquitoes and their spread is enhanced by rainfall, high humidity and high temperature. Malaria is a serious vector-borne disease caused by Plasmodium species is sadly fast spreading widely due to climate change. People in developing countries are most likely to be affected by the impact of climate change on malaria's expansion. Mosquitoes is the most significant fingerprint of climate change with respect to biotic invasion.