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| Gas Laws |
| The basic concept of gas laws and gases. |
Here you will learn about,
Gases
Boyle's law
Charles law
Avogadro’s law
Dalton's law of partial pressure
Graham's law of diffusion
Liquefaction of gases
Definition of Gas:
The matter is everything that occupies physical space. Matter examples include individuals, stones, water, and wind. The mass of a substance can be used to categorize it. The quantity of material that goes into making up a thing is its mass. Matter has four states, three are more common that are solid, liquid, and gas. The fourth state is plasma.
Any material which is neither solid nor liquid is referred to be a gas, such as hydrogen or oxygen. Gases conform to the shape of container in which they are kept because they have no fixed volume. Their molecules are spread away from each other and have Collison between them.
Gas laws:
“The relationship between volume of a given amount of
gas and the prevailing conditions of temperature and pressure are called gas
laws”.
Boyles Law:
Another name for Boyle's law is Mariotte's law. Boyle's
Law is a basic chemistry principle that defines how a gas responds when it
is maintained at a constant temperature. Robert A. Boyle discovered this rule
in 1662, and it states that "at a specific temperature, the volume of a
gas is inversely proportionate to the pressure it exerts."
In terms of mathematics, it is described as
OR
PV=K
P is the pressure of a gas, V is the volume of gas and K is constant.
The law can be stated as follows when considering the same material under two different types of circumstances.
P1V1=P2V2
Original pressure and volume are represented by P1 and V1
Second pressure and volume are represented by P2 and V2
Charles law:
Charles' law states that "assuming the pressure is constant, the volume occupied by a certain amount of gas is exactly proportional to its absolute temperature." The French Scientist J.-A.-C. Charles initially proposed this empirical relationship around 1787. It is also known as law of volume.
Mathematically it is written as
Ⅴ∝ T
⋁/T = K
Or
V=KT
Here V is the volume of gas, T is the temperature of the gas, measured in kelvin and K is the non-zero constant.
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Charles law |
The law may be expressed as follows for comparing the same material under two distinct types of circumstances:
Absolute Zero:
“The hypothetical temperature at which the
volume of gas is supposed to become zero if the gas remains in a gaseous state”. Absolute zero is not an attainable temperature.
0K= -273.16 ⸰C = -459 ⸰F
This law is obeyed only when the temperature
is taken on a Kelvin scale.
Mathematical equation of Charles law:
Vt = V0 (1+t/273)This equation is used to determine the increase or decrease of volume by a factor of 1/273 at any temperature (Vt). "t" is the temperature of the gas and is the volume of gas at zero centigrade.
Avogadro’s law:
Avogadro's
law states as “equal volumes of all gases, at the same temperature and
pressure, have the same number of molecules."
Mathematically this statement is written as,
Here V is the volume and n is the number of moles of gas ( amount of gas) and K is the constant for the given temperature and pressure of gas.
This law was named after Amedeo Avogadro in 1812, he gave the hypothesis that when two samples of an ideal gas, have the same volume and same temperature and pressure, they contain the same number of molecules. For example, Helium and nitrogen are two different gases but if they have same volume then they have an equal number of molecules.
For two different conditions, this law can be used and expressed as follows,
- Graphically this law is explained as,
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Avogadro’s law |
Examples:
H2
= 2g= 1 mole = 222.414 dm3 at STP = 6.02 × 1023
molecules
O2
= 32g = 1 mole = 222.414 dm3 at STP = 6.02 × 1023
molecules
CH4
= 16 g = 1 mole = 222.414 dm3 at STP = 6.02 × 1023
molecules
1
mole of H2 = 22.414 dm3 of H2 = 6.02 × 1023
molecules of H2
1 mole of NH3 = = 22.414 dm3 of NH3 =6.02 × 1023 molecules of NH3
Dalton’s law of partial pressure:
“The total pressure exerted by a
mixture of non-reacting gases is equal to the sum of their individual partial
pressure”.
Mathematically it is written as;
Pt = p1
+ p2 + p3
Partial pressure is the pressure of gas that it exerts
on the walls of a container if it has the same volume under same temperature.
For example;
Pt = pN2
+ pCH4 + pNH3
= (400+
500+100) torr
Pt = 1000 torr
So, this law expresses the total
pressure of different gases.
Graham’s law of diffusion:
This law was given by Thomas Graham
(1805-1869)
“It states as
the rate of diffusion or effusion of a gas is inversely proportional to the square root of their density at constant temperature and pressure.”
Mathematically it is written as;
Rate of diffusion = ,
Density is directly related to molecular mass, so above in equation M is used.
For molecular effusion, which includes the passage of one gas at a time through a hole, Graham's law is the most accurate. For the diffusion of one gas into another or in air, it can only be roughly applied because these processes include the movement of many gases.
The relationship between the molar mass and mass density holds true under identical temperature and pressure circumstances. As a result, the square roots of the mass densities of various gases are negatively correlated with their rates of diffusion.
Liquefaction of gases:
The general principle that applies here is that low temperature and high pressure, this the necessary condition for the liquefaction of gas. Low temperature brings molecules of gas close together and high pressure will help to convert the gas to a liquid state.
Critical Temperature (Tc):
The term "critical temperature" (abbreviated
as "Tc") refers to the greatest temperature at which a substance can
exist as a liquid.
The following variables affect it:
- Molecule size
- Molecular structure
- Interactions between molecules
Critical pressure
(Pc):
Critical pressure is defined as the pressure necessary
to cause liquefaction at a critical temperature.
Critical volume (Vc):
One mole of gas's volume is referred to as the
critical volume (Vc) when a gas is measured at its critical temperature and
pressure.
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