TYPICAL EXAMPLES & ESSENTIALS OF SURFACE CHEMISTRY 

::::THIS SECTION DESCRIBES SOME ESSENTIAL PRINCIPLES AND AS WELL AS SOME IMPORTANT EVERYDAY EXAMPLES

::::WHERE SURFACE CHEMISTRY APPLICATIONS ARE RELEVANT::::::::

 

 

I.....Distance Between Molecules:::

ALL MOLECULAR INTERACTIONS ARE
DEPENDENT ON THE DISTANCE BETWEEN MOLECULES--------

Example:::WATER ( at room temperature and pressure )

Volume of 1 mole water::::

Liquid = 18 cc

Gas = 22.4 Liters

Ratio of Volume of Gas:Liquid = ca. 1000

Ratio of distance in Gas:Liquid = (1000)exp 1/3 = 10

 

Actually, one may compare the states of solid - liquid - gas to how the people are arranged in any football arena, as follows::

...SOLID state...People sitting in chairs.

...LIQUID state...People moving out of the arena.

...GAS state...Football players running around

This simply shows the molecular picture of these three states of matter. Now, at the SURFACE of a liquid, the molecules move from a liquid phase (the distance between molecules is 10 times smaller than in the gas phase) to a gas phase. If we look closer, we find that these surface molecules are under asymmetrical force of ineraction. 

 

 

 

 

II....SURFACE TENSION OF A LIQUID

 

The subject of physical chemistry concerns with properties which are needed to describe any system. Therefore one needs to describe the molecules in the system as accurately as possible. It is thus of interest to understand the situation about the near neighbour molecules in any system.

Molecules in the bulk water (for example) are surrounded by twice as many neighbor molecules than a molecule at the surface. The ratio of near neighbor molecules (surface:bulk phase) is thus half for these two states. Surface tension thus acts to compensate for this difference.
In-fact, STEFAN suggested (almost a century ago!) that surface tension is about half of the enthalpy of vaporization. This is true for most symmetrical molecules.

 

 

 

III....Adsorption of Surface-active substances (soaps; detergents)

Ethanol is soluble in water. The surface tension of water (72 nM/m (dynes/cm)) reduces slowly to about 30 mN/m when ethanol is added to water. However, when soap or detergent is added to water the surface tension also decreases to about 30 mN/m. One needs about 50% ethanol to achieve the same effect as 1 g/liter for a typical detergent,

 

IV....Mercury or Detergent in Battery (dry cell zinc)..( POLLUTION & SURFACE CHEMISTRY )...

 

About 100 years ago the dry cell battery was invented. It consisted of zinc + mercury (30%) and other chemicals. The role of mercury was to control the passive zinc system when the battery was not under use. The modern dry cell battery is now based on using detergents (about 50 ppm) instead of mercury. This shows that surface chemistry has an important application in battery technology.

V....OIL SPILL & CLEANUP

Oil spill is a very important example of surface chemistry application process.

Oil and water do not mix. However, by reducing the interfacial tension (IFT) at oil - water interface, one can achieve emulsions. The IFT of oil - water is ca. 50 mN/m. By adding surface active agents (SAA) one can reduce IFT to less than 1 mN/m. On abrupt shaking the oil drops break-up into very minute size thus producing an emulsion. Such emulsions are created, for instance, in the clean-up of oil spills ( as in the Mexico Gulf ).

However, when the reservoir is at a high pressure ( every 1 km depth gives rise to ca. 100 atm pressure), then one must make investigations under high pressures in order to treat such oil spills. High pressure instruments are available in labs which can guide the techs to use the correct treatment procedure. For instance, hexadecane becomes solid around 30 atm pressure.

Furthermore, since the composition of oil differs from place to place, the chemicals needed for such process will be different. Thus the role of surface chemistry is a vital application area in this field of pollution problem.

VI..GAS RECOVERY & FRACKING PROCESSES
Fracking is a new industrial application of surface chemistry. In most simple terms one may describe this process as: natural gas is adsorbed to shale and is not easily desorbed from its surrounding material. Recently techniques have been developed which make it possible to recover enormous amounts of gas in Nort America, Russia, China and Europe. This is going to have an enormous impact on energy needs, especially when considering that gas is a much clean source for energy. In the USA the shale gas has increased enormously in the last decade, which has lead to great decrease in the gas prices. The fracking research on surface chemistry involved needs to be investigated, such that pollution  concerns can be controlled (if not eliminated) by using chemicals which are viable to mankind. This is well known situation in all pharmaceutical products. The process of fracking involves:
...adsorption of gas,
...solid - solid interactions in the shale,
...desorption of gas (mostly methane).

VII..Carbon Capture Processes (CCP)
CO2 in air can be captured by suitable adsorption techniques, in order to reduce CO2 concentration in the air. All coal energy plants can essentially be CO2 free if this technique is used optimal around the world. Carbon capture can theoretically remove 100% of CO2 from emission gasses. Since many countries, such as China, India and Poland, are forced to use cheap coal as source of energy, the carbon capture research should make it possible to use coal as a clean energy source. In-fact, due to shale gas production increase, the coal prices have decreased in the last decade. Currently a few large CCP are being implemented in USA and Australia. CCP can be very effective way to control and monitor CO2 concentrations (which is about 400 ppm). 
Actually, mankind is very dependent on water - oxygen - CO2 - sunshine! Therefore, one should be grateful that the concentration of CO2 is increasing slowly, and not DECREASING!


 

 
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