Chemistry Important Definations

8/10/2019 Chemistry Important Definations

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Chemistry Important Definitions

Boyle's Law: For a fixed mass o f gas at cons tant temperature, the volum e is inverselypropo rt ional to the pressure.

Charles' Law: For a fixed mass of gas at constant press ure, the volum e is direct lypropo rt ional to the Kelv in temperature.

Gay-Lussac's Law: For a fixed mass of gas at cons tant volum e, the pressure is direct lypropo rt ional to the Kelv in temp erature.

Avogadro's law: Equal volum es of al l gases, at the same temperature and pressure, have thesame numb er of mo lecules.


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Diffusion: Diffusion is the net mov ement of a subs tance (e.g., an atom, ion or m olecule) froma region of high c oncentrat ion to a region of low con centrat ion.

Effusion:Effusion is the proc ess in whic h a gas escapes through a sm all hole.

Graham's law of effusion:

Graham's law states that the rate of effusion or of diffusion of a gas is inversely proportional to thesquare root of its molecular weight.


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Mean Free Path: The mean free pathis the dis tance that a molecule travels betweencol l is ions.

Avogadros number:Avogadros numberis the number of units in on e mole of any

sub stanc e (defined as its mo lecular w eight in g rams ), equal to 6.022 10

23

. The units m ay beelectron s, atom s, ions, or molecules, depending o n the nature of the substance and the

character of th e reaction.

Modification of the Ideal Gas equation: Vander wells equation of state:

The van der Waals equation is a m odif icat ion to the ideal gas law that corrects for no n-zero gas

volum e and intermo lecular interact ions.

The Ideal Gas Law, PV = nRT, can be derived by assum ing th at the molecules th at make up th e

gas have negl ig ib le sizes, that their col l is ion w ith thems elves and the wall are perfect ly elast ic ,

and that the molecules have no in teract ions with each oth er.

The van der Waal 's equation is a second order approx imation of t he equation of state of a gas tha

wil l work even when the density of the gas is not low.

( )


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Behavior of Real Gases: Amagats Curve:

Adhesion:Adh esion is the force of attract ion between molecules of dif ferent substanc es.

Example:Water is attracted to other substances

Cohesion:Cohesion is the force of attract ion b etween mo lecules of the same substance.


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Example: water is attracted to water

Viscosity:Viscos ity is a measurement of how resistant a flu id is to attempts to m ove

through i t . A f lu id wi th a low v iscos i ty is sa id to be " th in ," whi le a high v iscos i ty f lu id is s a id to

be "thic k." It is easier to mo ve through a low vis cos ity f lu id (l ike water) than a high viscos ity

f lu id (l ike hon ey).

Surface Tension:Surface tension is th e energy, or wo rk, required to increase the surfacearea of a l iquid due to interm olecular forces. Surface tension forces are due to intermolecular

forces between the liquid's molecules at the liquid's outer boundaries.these intermolecular forces vary

depending on the nature of the liquid.

System: A sy stem is a col lect ion of elements or com ponents th at are organized for acommon purpose.

First law of thermodynamicsEnergy can neither be created nor destroyed. It can only chang

form s. In any proc ess, the total energy of the universe remains the same. For a thermody nami

cyc le the net heat suppl ied to the system equals the net work d one by the sys tem.

Example: you have a pot of water at room temperature. You add some heat to the system. First, the temperature

and energy of the water increases. Second, the system releases some energy and it works on the environment

(maybe heating the air around the water, making the air rise).

Second law of thermodynamics: in al l energy exchanges, if no energy enters or leaves the

sys tem, the potentia l energy o f the state wil l always be less than that o f the init ia l state.

A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car. Once the

potential energy locked in carbohydrates is converted into kinetic energy (energy in use or motion), the organism

will get no more until energy is input again. In the process of energy transfer, some energy will dissipate as heat.

LaPlace's Law : The larger the vessel radius, the larger the wall tensionrequired to withstand a given internal fluid pressure.


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Osmotic Pressure: Osmosis is the diffusion of a fluid through a semipermeable membrane.When a semipermeable membrane separates a solution from a solvent, then only solvent molecules areable to pass through the membrane.The osmotic pressur e of a solut ion is the pressure dif ferenceneeded to sto p the flow of s olvent across a semip ermeable memb rane. The osmotic pressure of

so lu t ion is proport iona l to the molar concentrationof the solute part ic les in solut io n.

Colligative Properties: Coll igat ive propert ies of solut ions are propert ies that depend upon theconc entrat ion of solute molecules or ions, but not upo n the identi ty of the solute.Colligativeproperties include:

vapor pressure lowering,

boiling point elevation,

freezing point depression,

and osmotic pressure.

Boiling point elevation:Boiling point elevation is a colligative property of matter. Boi l ing po inelevation occ urs wh en the boi l ing po int of a solut ion becom es higher than the boi l ing poin t of

a pure solvent.The temperature at which the solvent boils is increased by adding any non-volatile

solute.

A common example of boiling point elevation can be observed by adding salt to water. The boiling

point of the water is increased.

Freezing point depression:freezing point depression is a colligative property of matter.Freezing point depression o ccur s when the freezing point of a l iquid is lowered by adding

another comp ound to i t .The solution has a lower freezing point than that of the pure solvent.

For example, the freezing point of seawater is lower than that of pure water. The freezing point ofwater to which antifreeze has been added is lower than that of pure water.

Kownan Mursalin Mazed

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Chemistry Important Definations