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Gaseous state

Gaseous state. Lec .4. Gaseous state introduction. Matter exists in three distinct physical states: gas, liquid and solids.

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Gaseous state

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  1. Gaseous state Lec .4

  2. Gaseous state introduction • Matter exists in three distinct physical states: gas, liquid and solids. • The condition of gas depends upon three factors; pressure, volume and temperature. The relations between these three factors are governed by certain simple laws as results of: • gases can be easily compressed in to smaller volumes that are their densities can be applying increased pressure. • gases exert pressure on their surrounding, in turn; pressure must be exerted to confine gases. • gases expand without limits so gases completely and uniformly occupy the volume of any container. • gases diffuse into one another.

  3. Boyle’s Law • Gas volume and gas pressure are related by Boyle’s Law which states that “the pressure of a quantity of a gas is inversely proportional to its volume when temperature is fixed. V α 1/P or P=K*1/V → PV = constant (1)

  4. Boyle’s Law(cont.) When the pressure P plotted verses PV, straight line is obtained

  5. Charles Law • Gas volume and absolute temperature related by Charles’s Law which states that the volume of a gas is directly proportional to its absolute temperature, V/T = constant (2) • (V1/T1 = V2/T2) Charles Law

  6. Avogadro's law • Equal volumes of different gases at the same temperature and pressure, contain the same number of molecules“ • V α n (V1/n1 =V2/n2) From eq.1 &2 : • PV/T = K the gas constant and indicated by the symbol "R • (Since according to Avogadro's law one mole of any gas at 1 amt. 0°C or 273.16 absolute) occupies 22.414 litters. (1 atm. = 76 cm of mercury) R=(1*22.414)/ (1*273.16)= 0.08206 atm.L/mol.K

  7. It can be easily deduced that " the pressure of a definite mass of a gas is directly proportional to the absolute temperature if the volume of the gas is kept constant” i.e.: P/T = K at constant volume

  8. Let’s Review Gases at low pressures (gas particles are far apart) have following characteristics: • V α 1/P (constant temperature, fixed amount of gas) – Boyle’s Law (P1V1=P2V2) • V α T (constant pressure, fixed amount of gas) – Charles’ Law (V1/T1=V2/T2) V α n (at constant temperature and pressure) – Avogadro’s Law. Could be written as V = constant. n (linear plot) (V1/n1 =V2/n2) This means that if you double amount of gas molecules, volume would double if pressure is to remain constant.

  9. Combining three gas laws given above, we obtain: P1V1/n1T1 = P2V2/n2T2 This is the Ideal Gas Law which approximates the behavior for all gases at atmospheric pressure Because PV/nT = constant value (R), the Ideal Gas Law, which explains behavior of ideal/perfect gas, is written as: PV = nRT

  10. Example (1): Calculate the volume occupied by 11 grams of CO2 at 500 mm pressure and -10C (CO2=44). Solution PV = n R T P= 500/760 atm. T=-10+273=263K n=11/44=0.25 moles R=0.082 liters-atm.mole-1K-1 V = n R T / P = (0.25*0.082*263*760) / 500 =8.2 litters

  11. Example (2): How many moles of oxygen gas in a 10.0 L container can exert a pressure of 712 mm Hg at a temperature of 25C? • Solution PV = nRT

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