Tiêu đề 7_Behaviour of Gases.pdf ✅

PRE-MEDICAL 1 PHYSICAL CHEMISTRY Serial No. MODULE-1 Page No. 1. Some basic concepts of Chemistry 2. Atomic structure 3. Chemical Equilibrium 4. Ionic Equilibrium 5. Thermodynamics & Chemical Energetics 6. Redox reactions 7. Behaviour of Gases 8. Hints and Solutions
PRE-MEDICAL 2 BEHAVIOUR OF GASES S. No. CONTENTS Page No. 1. Introduction 2. Some definitions 3. Graham’s law of diffusion 4. Real Gases 5. Vander Waal’s gas Equation 6. Exercise-I (Conceptual Questions) 7. Exercise-II (Previous Years Questions) 8. Exercise-III (Analytical Questions) 9. Exercise-IV (Assertion & Reason)
PRE-MEDICAL 3 BEHAVIOUR OF GASES 6.0 INTRODUCTION Gaseous state is that state of matter where repulsive forces are dominating that attractive forces. For study of gases we require gas parameters like p, v, n and temperature. Gases having no interaction between gas molecules are known as ideal gases. They follow kinetic gas assumptions, kinetic gas equation, gas laws and ideal gas equation but certain gases which do not follow above conditions are known as real gases. 6.1 SOME IMPORTANT DEFINTIONS : (a) Diffusion :  The tendency of inter mixing of non-reacting gases spontaneously without external pressure. Or  The property of the spontaneous flow of gaseous molecules from high concentration to low concentration without external pressure. In diffusion, Pext = constant (b) Effuison :  The property of the flow of gaseous molecules form high concentration to low concentration form a pin hole with external pressure. Or  It is diffusion through pin hole which arises due to pressure difference. In effusion, Pext = variable (c) Rate of diffusion (r) : At constant temperature and pressure, the distance travelled by diffused gas or volume of diffused gas or moles of diffused gas per unit time is called as rate of diffusion. r = diffused gas (taken) t = diffused gas (taken) V t = diffused gas (taken) n t Grahm’s law of diffusion (Applicable for non-reacting gases) :-  At constant temperature and pressure, the rate of diffusion is inversely proportional to the square root the density. r  1 d (at constant T and P) r  1 VD r  W 1 M 1 1 2 2 2 2 1 2 1 1 r v t d M r t v d M    
PRE-MEDICAL 4  At constant temperature rate of diffusion is proportional to P d . 1 1 2 2 1 2 2 1 2 1 2 1 r v t d P M r t v d P M     7.2 REAL GASES : (i) Those gases which do not follow kinetic gas assumptions, kinetic gas equation, gas law’s and ideal gas equation are known as real gases. “At very low pressure and high temperature real gases behave as ideal gas.” (ii) Deviation of real gases from ideal gas behavior is mathematically denoted by “Z” named as compressibility factor. Z = real obs m obs ideal V V P P(V ) V nRT RT  Case I If Z = 1 ; ideal gas ; it signifies there is no interaction between gas molecules P(V ) m obs RT = 1  P(Vm)obs = RT Case II If Z > 1; positive deviation from ideal gas behavior ; signifies repulsive forces are greater than attractive forces so such gases can’t be liquefied easily. P(V ) m obs RT > 1  P(Vm)obs > RT Example H2, He Case III If Z < 1 ; Negative deviation from ideal gases behavior : it signifies attractive forces are higher than repulsive forces so gas can be liquefied easily. P(V ) m obs RT < 1  P(Vm)obs < RT The gas show the negative deviationgenerally at low pressure from ideal gas behavior . Example SO2, HCl, NH3. Figure 7.3 REAL GAS EQUATION OR VAN DER WAAL GAS EQUATION : PV = nRT .....(1) ideal gas equation Two major corrections are required for real gases (i) The intermolecular force of attraction between molecules is not negligible. Fatt  0 so Pact. = 2 real 2 n a P v        (ii) The volume of a molecule is not negligible in comparision of total volume of gas. V1  0 so Vact = (V – nb) B = covolume = exluded volume = 4× 3 4 r 3  From equation (i)