Tiêu đề 3_Chemical Equilibrium.docx ✅

PRE-MEDICAL 13 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 13 CHEMICAL EQUILIBRIUM S.No. CONTENTS Page No. 1. Introduction 2. Equilibrium and chemical process 3. Law of mass action 4. Degree of Dissociation 5. Application of law of mass action 6. Le-chatelier’s principle (a) Chemical Equilibrium (b) Physical Equilibrium 7. Reaction Quotient 8. Calculation of degree of dissociation by vapour density method 9. Exercise-I (Conceptual Questions) 10. Exercise-II (Previous Years Questions) 11. Exercise-III (Analytical Questions) 12. Exercise-IV (Assertion & Reason)
PRE-MEDICAL 13 CHEMICAL EQUILIBRIUM 2.0 INTRODUCTION Chemical reaction : Symbolic representation of any chemical change in term of reactants and products is called chemical reaction. Types of chemical reaction : (a) On the basis of physical state (I) Homogeneous reaction All reactants and products are in same phase. N 2 (g) + 3H 2 (g) ⇀ ↽ 2NH 3 (g) (II) Heterogeneous reaction Reactants and products are in two or more phases. Zn(s) + CO 2 (g) ⇀ ↽ ZnO(s) + CO(g) (b) On the basis of speed (I) Fast reactions (i) Generally these reactions are ionic reactions. HCl + NaOH  NaCl + H 2 O Acid Base Salt Water (ii) Rate determination is impossible. (II) Slow reactions (i) Generally these reactions are molecular reactions. H 2 + I 2  2HI (ii) Rate determination is possible. (c) On the basis of heat (I) Exothermic reaction (i) Heat is evolved in these type of chemical reactions. RP + x kcal (ii) Change in enthalpy, H = (–) ve (II) Endothermic reaction Heat is absorbed in these type of chemical reactions. R  P – x kcal H = (+) ve (d) On the basis of direction (I) Reversible reaction (i) Chemical reaction in which products can be converted back into reactants. N 2 + 3H 2 ⇀ ↽ 2NH 3 (ii) Produced in forward as well as in backward direction. (iii) Possible in closed container (iv) These can attain equilibrium (v) Reactants are never completely converted into products (vi) Neutralization reaction except strong acid and strong base. HCl + NH 4 OH ⇀ ↽ NH 4 Cl + H 2 O
PRE-MEDICAL 13 (II) Irreversible reaction (i) Chemical reaction in which products cannot be converted back into reactants. AgNO 3 + NaCl  AgCl NaNO 3 NaCl + H 2 SO 4 NaHSO 4 + HCl Zn + H 2 SO 4  ZnSO 4 + H 2  (ii) Produced only in one direction (forward direction) (iii) Generally possible in open container (iv) These do not attain equilibrium (v) Reactants are nearly completely converted into products. (vi) Neutralization reaction of strong acid and strong base. HCl + NaOH  NaCl + H 2 O GOLDEN KEY POINTS  We always take forward direction if direction is not specified.  In a reversible reaction if forward reaction is exothermic then the backward reaction will be endothermic and vice-versa.  Rate of Reaction The change in concentration of reactants or products in unit time is known as rate of the reaction. Rate of reaction = (±) changeinconcentration timetakenforthechange 3.1 EQUILIBRIUM AND CHEMICAL PROCESS (A) Chemical Equilibrium The most important characteristic property of a reversible reaction is that it always attains a state of chemical equilibrium. Consider a general reversible reaction in a closed vessel. A + B f b r r ⇀ ↽ C + D Where, r f = rate of forward reaction r b = rate of backward reaction Initially reaction occurs in forward direction but as the concentration of products increases reaction also starts in backward direction. At a certain stage, rate of forward reaction becomes equal to the rate of backward reaction called equilibrium state. At equilibrium state : Rate of forward reaction (r f ) = Rate of backward reaction (r b )