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

**Gases at STP –** H_{2}, N_{2}, O_{2}, F_{2}, Cl_{2}, O_{3}, 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

**NO _{2} and SO_{2} –** 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 = K_{1} at constant T (or)

P_{1}V_{1} = P_{2}V_{2} = K_{1}

**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 dm^{3} atm mol^{-1} K^{-1}

R = 8.314 × Pa m^{3} K^{-1}mol^{-1}

R = 8.314 × 10^{-2} bar dm^{3} K^{-1}mol^{-1}

R = 8.314 JK^{-1}mol^{-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.

P_{total} = p_{1}+P_{2} + P_{3} ……………..

**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 V_{c} = 3b

Critical Pressure P_{c} = \(\frac{a}{27 b^{2}}\)

Critical Temperature T_{c} = \(\frac{8 \mathrm{a}}{27 \mathrm{Rb}}\)

**Critical temperature of CO _{2} –** 303.98 K

**Critical Temperature –** T_{c} is defined as the temperature below which a gas can be liquefied by the application of pressure.

**Critical Pressure –** P_{c} is the pressure required to liquefy a gas at its critical temperature.

**Critical Volume –** V_{c} 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 ( T _{i}) –** The temperature below which a gas obey Joule Thomson effect is called inversion temperature. \(\mathrm{T}_{\mathrm{i}}=\frac{2 \mathrm{a}}{\mathrm{Rb}}\)