## Tamilnadu Samacheer Kalvi 11th Chemistry Notes Chapter 6 Gaseous State Notes

Gases at STP – H2, N2, O2, F2, Cl2, O3, He, Ne, Ar, Kr, Xe and Rn (Only 11 elements).

The Earth – The Earth is surrounded by a atmosphere of air whose composition is 78% Nitrogen, 21% Oxygen and 1% other gases.

Oxygen – It is highly essential for our survival.

Hydrogen cyanide (HCN) – Deadly poison

Carbon monoxide (CO) – Highly toxic

NO2 and SO2 less toxic

Chemically inert gases – He, Ne, Ar, Kr, Xe and Rn.

Gas – A substance is normally in a gaseous state at ordinary temperature and pressure.

Vapour – The gaseous form of any substance that is a liquid or solid at NTP. Gaseous State

Pressure – It is defined as the force exerted by a gas on unit area of the wall.
Pressure = $$\frac{\text { Force }}{\text { area }}=\frac{\mathrm{F}}{\mathrm{a}}$$

Unit of pressure (Pascal) – 1 Pascal = 1 Nm-2,where 1 N = 1 Kg m s-2. Other units of pressure are Bar, atmosphere, Torr, mm of Hg.

Atmospheric pressure – The force exerted on a unit area of earth by the column of air above it is called atmospheric pressure.

1 atm – 760 mm Hg

Boyle’s law – At a given temperature, the volume occupied by a fixed mass of a gas is inversely proportional to its pressure.
V ∝ 1/p at constant T (or)
PV = K1 at constant T (or)
P1V1 = P2V2 = K1

Charles’ law – For a fixed mass of a gas at constant pressure, the volume is directly proportional to temperature (K).
V ∝ T and constant P and n : V/T = Constant

Absolute zero : -273.15°C.

Gay-Lussac’s law – At constant volume, the pressure of a fixed mass of gas is directly proportional to temperature. P ∝ T at constant V ; P/T = Constant.

Avogadro’s hypothesis – Equal volumes of all gases under the same condition of temperature
and pressure contain equal number of molecules.
V ∝ n (or) $$\frac{\mathrm{V}_{1}}{n_{1}}=\frac{\mathrm{V}_{2}}{n_{2}}=\text { Constant }$$

Ideal gas equation – PV = nRT where R is universal gas constant.

Values of R –
R = 0.082057 dm3 atm mol-1 K-1
R = 8.314 × Pa m3 K-1mol-1
R = 8.314 × 10-2 bar dm3 K-1mol-1
R = 8.314 JK-1mol-1

Dalton’s law of partial pressures – It states that the total pressure of a mixture of gases is the sum of partial pressures of the gases present.
Ptotal = p1+P2 + P3 ……………..

Graham’s law of Diffusion – The rate of effusion or diffusion is inversely proportional to the square of molecular mass of a gas through an orifice.
$$\frac{r_{A}}{r_{B}}=\sqrt{\frac{M_{B}}{M_{A}}}$$

Ideal gases – Gases that obey ideal gas equation PV = nRT are ideal gases.

Real gases – Gases that do not obey the ideal gas equation PV = nRT are real gases. For them either PV > nRT or PV < nRT

Van der Waals equation of state –
$$\left(\mathrm{P}+\frac{\mathrm{an}^{2}}{\mathrm{~V}^{2}}\right)(\mathrm{V}-\mathrm{nb})=\mathrm{nRT}$$
Where a and b are Van der Waals constant.

Critical constants –
Critical Volume Vc = 3b
Critical Pressure Pc = $$\frac{a}{27 b^{2}}$$
Critical Temperature Tc = $$\frac{8 \mathrm{a}}{27 \mathrm{Rb}}$$

Critical temperature of CO2 303.98 K

Critical Temperature – Tc is defined as the temperature below which a gas can be liquefied by the application of pressure.

Critical Pressure – Pc is the pressure required to liquefy a gas at its critical temperature.

Critical Volume – Vc is the volume occupied by one mole of a gas at its critical temperature aftd critical pressure.

Joule Thomson effect – The phenomenon of producing lowering of temperature when a gas is made to expand adiabatically from a region of high pressure into a region of low pressure.

Inversion temperature ( Ti) – The temperature below which a gas obey Joule Thomson effect is called inversion temperature. $$\mathrm{T}_{\mathrm{i}}=\frac{2 \mathrm{a}}{\mathrm{Rb}}$$

Samacheer Kalvi 11th Chemistry Notes