Thursday, 30 August 2012

Gay-Lussac’s Law

Gay-Lussac's Law

Gay-Lussac's Law which is most often referred to as the Pressure law, was founded by a French Chemist & Professor Joseph Louis Gay-Lussac in 1809.
Gay-Lussac's Law has also been referred to as Charle's Law, but they are not the same.
Gay- Lussacs Law gives the relationship between pressure and temperature when volume and amount are held constant.
Gay-Lussac found that for a gas, if the pressure increases, the temperature increases, and if the temperature decreases, the pressure decreases. Based on this Gay-Lussac stated his law as " The Pressure of a fixed amount of Gas at a fixed Volume is DIRECTLY proportional to its Temperature ".

Mathematically the Law can be stated as :-

P α T or P = k T or P/T = k

P is the pressure of the gas in atmospheres,
T is the temperature of the gas in Kelvin &
k is a constant .
If P1 and T1 is the initial pressure and temperature of a gas,
Then according to Gay-Lussac's Law :
P1 / T1 = constant

After the change in pressure and temperature,
P2 / T2 = constant

Combining the two equations we get :
P1 / T1 = P2 / T2

This law holds true because Temperature is a measure of the Average Kinetic Energy of a substance and as the Kinetic Energy of a Gas increases, it's particles collides with the walls of the container more rapidly, thereby exerting an increased Pressure.

Thus from the Gay-Lussac’s law we can say that it may be dangerous to heat a gas in a closed container because the increased pressure might cause the container to explode.

Wednesday, 29 August 2012

Henry's Law

Henry's Law

Henry's Law is one of the Gas Laws formulated by a British Chemist William Henry in 1803.
It states that " At a constant Temperature the solubility of a Gas in a Liquid (unless it is highly soluble) is DIRECTLY proportional to the Partial Pressure applied to the Gas ".
Mathematically Henry's Law can be stated as :-
p = kH x c
p is the partial pressure of the solute in the gas above the solution,
c is the concentration of the solute,
kH is a constant known as the Henry's Law constant with the dimensions of pressure divided by concentration.
The Henry's constant depends on the solute, solvent and the temperature.
The Henry's law constant "kH" is different for every gas, temperature and solvent .

A very good example of Henry's Law is Carbonated soft drinks. We know that in such drinks carbondioxide gas is at the top and the drink below it. Also some amount of carbondioxide is dissolved in the drink. When the bottle is sealed the pressure at the cap of the bottle is greater than the Atmospheric Pressure,But as soon as the bottle cap is opened the carbondioxide gas escapes which is indicated by the "phiss" sound heard when the cap is opened. Due to this,the Pressure at the cap of the bottle drops down the Atmospheric Pressure and some carbondioxide comes out of the drink in the form of bubbles.If the drink is left open for sometime the carbon dioxide in the drink will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat". One key thing to remember in this example is that the pressure acting above the drink in a sealed bottle is due to the partial pressure of carbondioxide.Thus from this example and according to Henry's Law we can say that more the partial pressure of carbondioxide more will be it's solubility in the drink.

Monday, 27 August 2012

Charle's Law

Charle's Law

Charles' Law describes "How Gases tend to expand when heated" and gives the direct relationship of Temperature and Volume of a gas.
Charle's Law states that " At a constant Pressure, the Volume of a confined gas is DIRECTLY Proportional to the Absolute Temperature " i.e ,V α T , thus if the Temperature of a gas is Doubled, it's Volume is also Doubled.

In a Simple one statement Charle's Law can be stated as " As the Temperature Increases the Gas Expands "
This occurs because as the temperature increases,the Gas molecules begins to move around quickly, hit the walls of the container with forces, resulting in the increase in Volume.

The Law was discovered by Jacques Charles in 1780's,But was first published in 1802 by a French Philosopher Joseph Louis Gay-Lussac who credited the discovery of an unpublished work.

Mathematically the Law can be stated as :-
Volume = Constant x Temperature or
V = kT .

Charle's Law must be used only with the Kelvin Temperature scale as this scale is an Absolute Temperature scale.

Boyle's Law or Mariotte's Law or Boyle-Mariotte Law

Boyle's Law

Boyle's Law states that " At a constant Temperature, the Volume of a confined gas ( gas restricted to certain limits,for eg., gas in a closed system ) is INVERSELY proportional to the Pressure to which it is subjected ".

The Law was named after a Chemist and Physicist Robert Boyle , who published the Law in 1662.

Robert Boyle studied the Compressibility of Gases in 1660. In his Experiments he observed that "At a fixed Temperature, the Volume of a gas is inversely proportional to the Pressure exerted by the gas."
For Eg :- If the Volume is Halved, the Pressure is Doubled and if the Volume is Doubled, the Pressure is Halved. The reason for this effect is that a Gas is made up of loosely spaced molecules moving randomly. Thus if a gas is Compressed in a vessel, the molecules are pushed together and the gas occupies less Volume. Due to this the molecules having less space to move, hit the walls of the vessel thus exerting an increased Pressure.

Mathematically the Law can be stated as :-
Pressure x Volume = Constant or
PV = k .

The value of the constant k depends on the units used for the other quantities,but once the units are fixed, k is also fixed.

When any one of the quantities V, P, or T are changed, one or two of the others must change so that the equation above still remains true.

A French Physicist Edme Mariotte discovered the same law independently of Boyle in 1676, and hence sometimes Boyle's Law is also referred to as Mariotte's or the Boyle-Mariotte law.

Friday, 24 August 2012

Avogadro's Law & Avogadro's Number

Avogadro's Law

Avogadro's law is a Gas Law which states that " Equal Volumes of Gases under the same Temperature and Pressure conditions will contain equal number of particles (atoms, ion, molecules, electrons, etc.) regardless of their Chemical nature and Physical properties " .
The law is named after an Italian Chemist Amedeo Avogadro who, in 1811, analysed that the two given samples of an ideal gas , of the same Volume and at the same Temperature and Pressure , contains the same number of molecules .
Mathematically the law can be stated as :-
V/n = k
V is the volume of the gas,
n is the amount of substance of the gas &
k is a proportionality constant.

Avogadro's Number

Avogadro's number is one of the fundamental constants of Chemistry and a dimensionless quantity represented by N having a numerical value of 6.022 14 × 10 23 mol -1 .