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  Other properties of Gases, Physics tutorial

Dalton's Law of Partial Pressure:

A closed vessel may have a mixture of gases. For instance when the gas is being made and gathered over water. The space in gas jar will have not only gas being together but also some water vapor.

Closed vessel with some water inside it may also have mixture of air and saturated water vapor. There is equilibrium between vapor phase and liquid phase. Dalton's law of partial pressure explains pressures of two gases in a container. Therefore, in study of chemistry, when the gas is being made and gathered over water, there is the circumstances whereby gas applies its own pressure while saturated water vapor pressure also plays a part.

Dalton's law of partial pressure defines that: in the mixture of gases, the total pressure is the sum of pressures of parts or individual gases every gas occupying volume of mixture e if gases don't reach chemically with one another. When we have the mixture of air and water vapor, we generally apply gas laws to air. We don't apply the laws to water vapor. This is due to mass of water vapor may modify through condensation as it takes place when temperature falls. We hence can't apply gas were there are changes in pressure and temperature.

Every gas is assumed to be the ideal gas.

Ptotal = P1 + P2 + P3 + . .

Where P1 and P2 are partial pressure of gas 1and gas 2 in mixture. As every gas behaves independently, ideal gas law can be utilized to compute pressure of that gas if we know number of moles of gas, total volume of container, and the temperature of the gas.

P1 = n1RT/v

Each gas exerts the same pressure they would exert if they were in the container alone.

The total pressure can be expressed as

Ptotal = Σi=1n or

Ptotal = P1 + P2 +....+ Pn

Where P1, P2 ...Pn represent the partial pressure of each component.

Graham's Law of Diffusion of Gases:

Gases are always in random motion. They move from region of high concentration to region of low concentration until the state of equilibrium is attained. Gases also been seen to move or pass through porous membranes or pots. Movement from region of higher concentration to low region of concentration is what is explained as diffusion. Graham established law which directs diffusion of gases as they pass through porous membranes or porous pots.

Graham's Law of diffusion of gases defines that rates of diffusion of gases through the porous membrane or pot under provided conditions are inversely proportional to square roots of the densities.

To describe this law, consider samples of two different gases at same Kelvin temperature.

As temperature is proportional to kinetic energy of gas molecules, kinetic energy (KE) of two gas samples is also the same.

In equation form, we can write this:

KE1 = KE2

As KE = (1/2) mv2, (m = mass and v = velocity) we can write the given equation:

m1v12 = m2v22

Note that value of one-half cancels.

The equation above can be rearranged algebraically into the following:

√(m1 / m2) = v2 / v1

You may want to guarantee for the correctness of rearrangement.

Graham's Law is frequently defined as follows:

r1 / r2 = √(MM2 / MM1)

Where MM signifies molar mass of substance in question. Frequently, in these kinds of problems, find out molar mass of the unknown gas.

Frequently rate of effusion of one gas is given relative to rate of effusion of the other gas. That permits you to set rate of effusion for one of the gases to the numerical value of 1. This is used frequently, look for it.

Avogadro's Law:

Avogadro's law has been very helpful in chemistry. For instance, it allows chemists to infer fact that some gases like oxygen, hydrogen and chlorine are diatomic. Chemists were able to utilize volumes of reacting gases to infer number of molecules involved in chemical reaction. For instance experiments have illustrated that one volume of hydrogen will react with one volume of chlorine to generate two volumes of hydrogen chloride.

H(1 vol) + Cl(1 vol) → HCl(2 vols)

With Avogadro's law we can say that, 1 molecule of Hydrogen will react with 1 molecule of Chlorine to generate 2 molecules of Hydrogen Chloride. To generate 2 molecules of HCl means that 1 molecule of Hydrogen will be H2 while one molecule of Chlorine will be Cl2. I.e., both Hydrogen and Chlorine are diatomic. Avogadro's law defines that, equal volumes of all gases under similar conditions like temperature and pressure contain equal numbers of molecules.

Mathematical form of Avogadro's Law is: V ÷ n = k

This signifies that volume-amount fraction will always be same value if pressure and temperature remain constant.

Let V1 and n1 be a volume-amount pair of data at beginning of experiment. If amount is changed to the new value called n2, then the volume will change to V2.

We know this: V1 ÷ n1 = k

And we know this: V2 ÷ n2 = k

As k = k, we can conclude that V1 ÷ n1 = V2 ÷ n2.

This equation of V1 ÷ n1 = V2 ÷ n2 will be very useful in solving Avogadro's Law problems. The Law done up in fractional form:

V1/n1 = V2/n2 V1n2 = V2n1

Avogadro's Law is a direct mathematical relationship.

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