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(c) Avogardo's Law : Equal volume of all gases under same conditions of temperature & pressure contain equal no of molecules. V = Kn But n =  (m = mass, M = Molar gas)
 V = = Kd d
density => density of gas is directly proportional to its molar mass. M  d |
III. Ideal Gas Equation
:
Volume of constant K depends only upon amount of gas taken. If n is no. of moles of gas taken. | K n | R Universal gas constant.  = nR PV = nRT Ideal Equation.
Derivation
:According to Boyles law  at constant T ................................................................ (1) According Charle's law V T at constant P ................................................................ (2) According to Avogardo's law V n at constant T & P ................................................................ (3) Combing (1), (2) & (3) x T x n=> PV = nRT K.......
Ideal Gas Equation (in terms of density) :If M is mass of gas in gm & M is molar mass of gas, then n =
PV =RT =RT P =
Volume of Gas constant (R) : R =  = 0.082 L atm K -1mol-1In SI unit R = 8.314 J K-1 mol -1 In terms of calori e R =  = 1.987 Cal K -1mol-1>
Illustration
: Temperature at foot of mountain is 300 C & pressure is 760 mm whereas at top of mountain there are 00 C & 710 mm. Compose densities at top & bottom of mountain. Ans: d =  
If two or more unreaching gases are enclosed in a vessel, total pressure exerted by gaseous mixture is equal to sum of all partial pressures that eact gas would exert when present alone in same vessel at vessel temperature. | P = P1 + P2 + P3 + .................. + Pn |
Applications
: (i) In determination of pressure of dry gas e: | Pdry gas = Pmoist gas - Aqueous tension |
Dumb Question
: What is equation tension ? Ans: Pressure exerted by water vapours in moist gas. (ii)In calculation of partial pressure : PV = nRT PA= nB  PB= nB PA& P B
Partial pressure.
By Dalton's law Total pressure, P = PA+ PB+ PC+ ................... =(nA+ nB+ nC+ ..................)
 = xA(mol.Fraction of A)
Question
: 270C & 746.5 mm pressure. Calculate volume of gas at 00C & 760 mm pressure (Aq. tension at 270C is 26.5 mm). Ans: [Dumb question: Why there is no ag. tension at 00C ? Ans: At 00 C, there is no water vapours. So, no, ag. tension at 00C.] Initial Condition Final conditionV1= 38 ml V2= ?P1= 746.5 - 26.5 P2= 760 mm = 720 mm T1= 27 + 273 = 300 K T2= 0 + 273 = 273 K By gas equation
V2= 32.76 ml.
Illustration
: A gaseous mix contains 56g N2, 44g CO2& 16g CH4 . Total pressure of mix is 720 mm Hq. What is partial pressure of CH4? Ans: nN2= 56/28 = 2 nCO2= 44/44 = 1 nCH4= 16/16 = 1 nTotal = 2 + 1 + 1 = 4 
x Total pressure = 1/4 x 720 = 180 mm.
Diffusion
: Spreading of molecules of a gas throughout available space.
Sffusion
: In this process gas under pressure escapes out of fine hole. At constant temperature & pressure, rates of diffusion of different gases are inversely proportional to square root of their densities.
Rate of diffusion/effusion = 
Note: If pressure is different of two gases then greater pressure, greater is no. of molecules hitting per unit area, greater is rate of diffusion.
r1 = v1/t r2 = v2/t
v1 Volume diffused of I gas.
v2 Volume diffused of II gas.
 Time ia constant for two gases.
 Volume of two gases is constant.
Question: 200 c,, HCl gas & NH3 are allowed to enter. At what distance NH4Cl will Ist appear ?
Ans: By Graham's law of diffusion
Thus, NH3 travels 1.465 times faster than HCl.
In other words. Since area of x-section is square, NH3 will travel 1.465 cm in same time in which HCl travel 1 cm.
Length of tube = 200 cm
Distance travelled in tube by NH3 =  x Total distance
 x 200 = 118.9 cm
So, NH4Cl will Ist appear at distance of 118.9 cm from NH3 and or 81.1 cm from HCl end.
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