Tiêu đề 1.CHEMICAL KINETICS VOL-2_CW_1 TO 92.pdf ✅

IX–Chemistry (Vol – II) Olympiad Text Book 1 Narayana Group of Schools Olympiad Class Work Book CONCEPT FLOW CHART CHEMICAL KINETICS Collision theory Transition state theory Molecularity Reaction Rate Order Rate Law Rate Constant Factors Affecting on Rate of a reaction ARRHENIUS [1859 – 1927] ARRHENIUS : “ARRHENIUS”(1859-1927) was a swedish physicists and physical chemist known for his theory of electrolytic dissociation and his model of the green house effect. At the age of Three,arrhenius taught himself to read without the encouragement of his parents ,and he watching his father’s addition of numbers in his account books,become an arithmaetical prodigy. In 1903 he was awarded the nobel prize for chemistry. CHEMICAL KINETICS
IX–Chemistry (Vol–II) 2 Narayana Group of Schools Olympiad Class Work Book CHEMICAL KINETICS Introduction: Chemical Kinetics: The branch of chemistry which deals with the rate of chemical reactions and factors (like temperature, pressure, catalyst etc.) which influences the rate of reactions and mechanism by which the reaction proceed is called chemical kinetics. Chemical Kinetics Vs thermodynamics: Thermodynamics tells about only the feasibility of a reaction where as chemical kinetics tells us about the rate of reaction and conditions by which the reaction rates may be altered.  For example thermodynamic data indicates that diamond shall convert to graphite but in reality this conversion rate is so slow that we can say that the change is not possible at all. Therefore it is said that diamond is forever.  There are two principal reasons for studying chemical kinetics i) To predict the rate of a particular reaction under specified conditions: a) The conditions can be adjusted to make the reaction to go a desired rate either rapidly or slowly or moderately b) It is used in industry for maximum yield ii) To predict the mechanism of the reaction: The intelligent guess regarding various elements any process responsible for the formation of products can be made which should be consistent with experimental data.  Based on the velocity (rate) of chemical reactions, the reactions are classified into three types a) Very fast (or) instantaneous reactions: The chemical reactions which are completed with in the fraction of seconds are called as very fast reactions. Example : 1) Neutralisation between strong acids and strong bases NaOH HCl NaCl H O aq aq aq l      2      2) Precipitation reactions 2 2 4   4      BaCl Na SO BaSO NaCl aq aq s aq    2 3) Explosion of TNT (trinitro toluene) 4) H OH H O2    
IX–Chemistry (Vol – II) Olympiad Text Book 3 Narayana Group of Schools Olympiad Class Work Book  It may be noted that these reactions involves only exchange of ions and no bonds are broken. Therefore they occur very fast.  These reactions occurs in about 12 10 to 16 10 seconds. b) Very slow reactions: These are chemical reactions which are extremely slow that they take months together to show any measurable change at room temperature Example: 1) 2 2 2 2 2 Room temperature H O H O   2) 2 2 NO O NO   2 2 3) Rusting of Iron 4 3 2 Fe O X H O Fe O X H O     2 2 2 3 2 4) 2 2 Room temperature C O CO   c) Moderate reactions:  The chemical reactions which are completed within few hours (or) minutes are called as moderate reactions  Mostly these reactions are molecular in nature. Example: 1) Decomposition of hydrogen peroxide 2 2 H O H O O 2 2 2 2   2) CH O CO H O 4 2 2 2    2 2 3) Inversion of cane sugar         Glucose Fructose C H O H O C H O C H O 12 22 11 2 6 12 6 12 aq l aq aq 6 6    4) Hydrolysis of ester CH COOC H H O CH COOH C H OH 3 2 5 2 3 2 5 aq l aq aq           5) NO Cl NOCl   2 2 It is not possible to determine the rate of very fast reactions and very slow reactions.Because the rate of reactions with moderate speed can be determined. Rate of reaction (or) Reaction rate:  You must be knowing that speed of an automobile is expressed in terms of change in position of distance covered by it in a certain period of time similarly the rate of a chemical reaction is a measure of the speed with which the reactants are converted into products.
IX–Chemistry (Vol–II) 4 Narayana Group of Schools Olympiad Class Work Book  Rate of reaction is defined as decrease in the concentration of reactant per unit time or increase in the concentration of the product per unit time. Example: Consider a hypothetical reaction R P   In which one mole of reaction ‘R’ produces one mole of the product ‘P’. The rate of the reaction may be expressed in either of the following two ways. i) The rate of disappearance of decrease in concentration of R (reactants) Rate of reaction Decrease in concentration of R time taken  ii) The rate of increase in concentration of P (products) Rate of reaction Increase in concentration of P time taken   If [R] and [P] are the concentration of R and P respectively at time 1 t and  2 R and  2 P are their respectively concentrations at time 2 t then dt t t  2 1       2 1 d R R R   and       2 1 d p p p   Then rate of reaction d R d p     dt dt     Units of rate of reaction: Rate of reaction change in concentration time taken  (i) For aqueous phase units are (mole/litre)/time (or) 1 1 mole lit sec     (ii) For gaseous phase units are     1 1 / sec .sec   atm time or atm or bar