Title 2.CHEMICAL EQUILIBRIUM VOL-2 CW 93 TO 159.pdf ✅

IX–Chemistry (Vol – II) Olympiad Text Book 93 Narayana Group of Schools Olympiad Class Work Book CONCEPT FLOW CHART CHEMICAL EQUILIBRIUM Rate of reactions Reversible & Irreversible reactions Equilibrium Types of Equilibrium Homogeneous Equilibrium Heterogeneous Equilibrium Law of mass action Equilibrium constant Relation between KP & KC Applications of Equilibrium constant Le chatelier’s principle
IX–Chemistry (Vol–II) 94 Narayana Group of Schools Olympiad Class Work Book Henry Louis Le Chatelier [1850 – 1936] * Born in Paris, france on OCtober in, 1850. * Died in Mirible-les Echelles, France on september 17, 1936. * Comes from a Roman catholic family. * Married Genevieve Nicolas and had seven chilldren. Historical Happenings: * His first research was in the chemistry of cements, and he discovered that the process of solution and solidification results in,Coherent mass. * French mineralogist Ernestfrancois Mallard had helped Le chatelier conduct experiements on explosive materials and this was his first published works of scientific research. * He is best known for Le Chatelier’s principle, which makes it possible to predict the effect a change of conditions will have on a chemical reaction, in 1884. * In 1907, Le chateller was elected to the French Academy of Science. And he recieved the jerome ponti and Lacaze Prizes award. CHEMICAL EQUILIBRIUM
IX–Chemistry (Vol – II) Olympiad Text Book 95 Narayana Group of Schools Olympiad Class Work Book CHEMICAL EQUILIBRIUM Chemical Reaction: Introduction Symbolic representation of any chemical change in terms of reactants and prod- ucts is called chemical reaction.  i) It is observed that in any chemical reaction, the concentration of the reactants progressively decrease with time of reaction and at the same time the concentration of the products gradually increase with time of reaction.  ii) Rate of Reaction: The rate of a reaction is generally defined as the change in molar concentration of a species under study per unit time.   Change in molar concentration of reactants (or) Products Rate of reaction time s  R ate o f re a ctio n Time Factors affecting the Rate of reaction: Nature of Reactants : Due to the difference in the relative stabilities (or) the electron structure of substances involved, the rate of reaction vary widely with the nature of reacting substances. State of division of the reacting substance: The more finely divided reacting substances are, more rapid in the reaction. Reaction medium: The reaction between materials in their solid state are generally slowerthan reactions between their liquid (or) gaseous state. The nature of solvent also affects the rate of reaction. Temperature: An increase in temperature invariably increases the rate of a chemical reaction. The rate of a reaction becomes just about double (or) triple for every 10oC rise in temperature. Catalysts: There are some substances which themselves appear to remain chemi- cally unchanged in reaction while they change the speed of certain reactions. They are called Catalysts.
IX–Chemistry (Vol–II) 96 Narayana Group of Schools Olympiad Class Work Book Pressure: If one (or) more gases are involved in the reaction changes in pressure may have decisive effects on the rates, of such reaction. Concentration: The rate of a reaction at any instant is directly proportional to the product of the concentrations of the reactants taking part in the reaction at that instant. Reversible and Irreversible reactions: i) Chemical reactions are classified into two types ‘based on the direction’ of the product formation. They are irreversible and reversible reactions. Irreversible reactions: A chemical reaction in which products do not react among themselves to form the original reactants is known as an irreversible reaction. Characteristics of irreversible reaction:  There, the reactants are completely changed into products, but the products cannot be changed into reactants. i) They proceed in one direction ie, they are unidirectional (one sided  ). Gen- erally possible in open container. These do not attain equilibrium. Examples: i) When magnesium reacts with oxygen it forms magnesium oxide.   2   2 2 Mg O MgO s s   ii) When silver nitrate solution is added to aqueous sodium chloride solution, a white precipitate is formed due to the formation of silver chloride. 3 3             AgNO NaCl AgCl NaNO aq aq s aq iii) When sodium sulphate is added to barium chloride, a precipitate of barium sulphate is formed. 2 4 2 4         Na SO BaCl BaSo NaCl aq aq s aq    2  In the above reactions, the reactants react completely and the reactions proceed only in the forward direction. Backward reactions in these cases are not possible. So, we can say that,  i) Generally, all ionic reactions, explosion reactions, combustion reactions, precipitation reactions are irreversible.  ii) Reactions in which gaseous products are formed are also irreversible when carried out in open vessels. Reaction in open vessel: Even a reversible reaction becomes irreversible if it is carried out in an open vessel. Example:             3 2 4 2 3     s s g s g g CaCO CaO CO NH HS NH H S