Lecture 5. Chemical kinetic. Rate of reaction Prepared by PhD Falfushynska H.

Slides:



Advertisements
Similar presentations
Is a study of how fast chemical reactions occur.
Advertisements

Chemical Kinetics Reaction rate - the change in concentration of reactant or product per unit time.
Chapter 12: Chemical Kinetics
AP Chapter 14.  Chemical kinetics is the area of chemistry that involves the rates or speeds of chemical reactions.  The more collisions there are between.
Chapter 14 Chemical Kinetics In kinetics we study the rate at which a chemical process occurs. Lecture Presentation © 2012 Pearson Education, Inc.
Chapter 13 Chemical Kinetics
Chapter 13 Chemical Kinetics
Chapter 16: Kinetics Rates and Mechanisms of Chemical Reactions 16.1 Factors That Influence Reaction Rate 16.2 Expressing the Reaction Rate 16.3 The Rate.
Copyright 1999, PRENTICE HALLChapter 141 Chemical Kinetics Chapter 14 David P. White University of North Carolina, Wilmington.
Prentice Hall © 2003Chapter 14 Chapter 14 Chemical Kinetics CHEMISTRY The Central Science 9th Edition David P. White.
Reaction Rate Change in concentration of a reactant or product per unit time. [A] means concentration of A in mol/L; A is the reactant or product being.
Chapter 14 Chemical Kinetics
Chapter 14 Chemical Kinetics
Chapter 12 Chemical Kinetics. Chapter 12 Table of Contents Copyright © Cengage Learning. All rights reserved Reaction Rates 12.2 Rate Laws: An.
Chemical Kinetics Unit 11.
Chapter 14 Chemical Kinetics. Kinetics is the study of how fast chemical reactions occur. There are 4 important factors which affect rates of reactions:
Chapter 14 Chemical Kinetics
Chemical Kinetics Chapter 14 AP Chemistry.
Chemical Kinetics Chapter 12.
Ch 15 Rates of Chemical Reactions Chemical Kinetics is a study of the rates of chemical reactions. Part 1 macroscopic level what does reaction rate mean?
Chapter 15 Rates of Reaction.
Dr. Floyd Beckford Lyon College
Prentice Hall © 2003Chapter 14 Chapter 14 Chemical Kinetics CHEMISTRY The Central Science 9th Edition.
Chemical Kinetics Chapter 14 Chemical Kinetics. Chemical Kinetics Studies the rate at which a chemical process occurs. Besides information about the speed.
Chapter 12 Chemical Kinetics. Chapter 12 Table of Contents Copyright © Cengage Learning. All rights reserved Reaction Rates 12.2 Rate Laws: An.
Chemical Kinetics. Kinetics In kinetics we study the rate at which a chemical process occurs. Besides information about the speed at which reactions occur,
Chapter 15 Chemical Kinetics: The Rate of Chemical Reactions.
Chemical Kinetics CHAPTER 14 Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson, Brady, & Hyslop.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Kinetics Chapter 13.
Chapter 12 Chemical Kinetics.
Chemical Kinetics 1 Chemical kinetics Plan 1. The subject of a chemical kinetics. 2. Classification of chemical reactions. 3. Determination methods of.
Chapter 12 Chemical Kinetics How often does Kinetics appear on the exam? Multiple-choice 4-8% (2-5 Questions) Free-response: Almost every year Kinetics:
C h a p t e r 12 Chemical Kinetics. Reaction Rates01 Reaction Rate: The change in the concentration of a reactant or a product with time (M/s). Reactant.
Chemical Kinetics. Kinetics Kinetics in chemistry is concerned with how quickly a reaction proceeds Factors that affect rate Physical state of the reactants.
1 Chemical Kinetics The area of chemistry that concerns reaction rates. The area of chemistry that concerns reaction rates.
Chapter 14 Chemical Kinetics. Review Section of Chapter 14 Test Net Ionic Equations.
Chapter 14 Chemical Kinetics. Review Section of Chapter 14 Test Net Ionic Equations.
Rate Expression VIDEO AP 6.1. Collision Theory: When two chemicals react, their molecules have to collide with each other with proper energy and orientation.
Chemical Kinetics Kinetics – how fast does a reaction proceed?
Chemical Kinetics Chapter 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 Reaction Mechanism The series of steps by which a chemical reaction occurs. A chemical equation does not tell us how reactants become products - it is.
1 Chemical Kinetics Chapter 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 14 Chemical Kinetics (part 2). The Collision Model Goal: develop a model that explains why rates of reactions increase as concentration and temperature.
Chapter 14 Chemical Kinetics (part 2). The Collision Model Goal: develop a model that explains why rates of reactions increase as concentration and temperature.
Chemical Kinetics “Rates of Reactions”. Reaction Rates Average rate: Change of reactant or product concentrations over a specific time interval Initial.
Chapter 14 Chemical Kinetics John D. Bookstaver St. Charles Community College Cottleville, MO Lecture Presentation © 2012 Pearson Education, Inc.
Chapter 14 – Chemical Kinetics The rate of a chemical reaction is the speed at which products or formed and reactants broken down. There factors that affect.
Chemical Kinetics Chapter 13. Chemical Kinetics Thermodynamics – does a reaction take place? Kinetics – how fast does a reaction proceed? Reaction rate.
Chapter 14 Chemical Kinetics Dr. Subhash Goel South GA State College Douglas, GA Lecture Presentation © 2012 Pearson Education, Inc.
Chemical Kinetics Chapter 13
The balanced chemical equation provides information about the beginning and end of reaction. The reaction mechanism gives the path of the reaction. Mechanisms.
Chem Physical Chemistry II
Prentice Hall © 2003Chapter 14 Chapter 14 Chemical Kinetics CHEMISTRY The Central Science 9th Edition David P. White.
Chpt 12 - Chemical Kinetics Reaction Rates Rate Laws Reaction Mechanisms Collision Theory Catalysis HW set1: Chpt 12 - pg , # 22, 23, 28 Due Jan.
LECTURE 6 A chemical kinetics of biological processes associate. prof. Yevheniya B. Dmukhalska.
Chemical Kinetics Chapter 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Kinetics Big Idea 4: Rates of chemical reactions are determined by details of the molecular collisions.
Chemical Kinetics. Fundamental questions: 1.Will it take place? Thermodynamics 2.If it does, how long will it take to reach completion or equilibrium?
Dr. Paul Charlesworth Michigan Technological University Dr. Paul Charlesworth Michigan Technological University C h a p t e rC h a p t e r C h a p t e.
Chapter 13 Chemical Kinetics CHEMISTRY. Kinetics is the study of how fast chemical reactions occur. There are 4 important factors which affect rates of.
Prentice Hall © 2003Chapter 14 Chapter 14 Chemical Kinetics CHEMISTRY The Central Science 9th Edition David P. White.
1 Chemical Kinetics Part 3: Reaction Mechanisms Chapter 13.
Chapter 14 Chemical Kinetics
Chemical Kinetics Unit 10 – Chapter 12.
Chapter 14 Chemical Kinetics
The Rate Law The rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised to some.
Chemical Kinetics Lesson 2
Chemical Kinetics Chapter 14.
Reaction Mechanisms The balanced chemical equation provides information about the beginning and end of reaction. The reaction mechanism gives the path.
Presentation transcript:

Lecture 5. Chemical kinetic. Rate of reaction Prepared by PhD Falfushynska H.

Type of chemical reactions after numbers of stages Simple one elemental step Complex Several steps А В Bilateral : А В : В Parallel or competitive reactions : ВА С : А →В→С Consecutive : А →В→С : А D Conjugation : А D С В Е В Е

Nuclear chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. A possible nuclear fission chain reaction. 1. A uranium-235 atom absorbs a neutron and fissions into two new atoms, releasing three new neutrons and a large amount of binding energy. 2. One of those neutrons is absorbed by an atom of uranium-238, and does not continue the reaction. However, one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and more binding energy. 3. Both of those neutrons collide with uranium-235 atoms, each of which fissions and releases a few neutrons, which can then continue the reaction.

Rice-Hertzfeld Free Radical Chain Reaction Mechanism Overall Reaction: Proposed Mechanism:

Classification of chemical reactions : homogeneous reaction (occur in a single phase (gaseous, liquid, or solid) : N 2 (g) + H 2 (g) → NH 3 (g) : heterogeneous reaction (occur in different phase) : Mg (s) + HCl (aq) → MgCl 2 (aq) + H 2 (g) topochemical reactions (occurs at the boundary of solid phases СuO + C Cu + CO

The balanced chemical equation provides information about the beginning and end of reaction. The reaction mechanism gives the path of the reaction. Mechanisms provide a very detailed picture of which bonds are broken and formed during the course of a reaction. Elementary Steps Elementary step: any process that occurs in a single step. Reaction Mechanisms

Elementary Steps Molecularity: the number of molecules present in an elementary step. –Unimolecular: one molecule in the elementary step, –Bimolecular: two molecules in the elementary step, and –Termolecular: three molecules in the elementary step. It is not common to see termolecular processes (statistically improbable). Reaction Mechanisms

Rate Laws for Elementary Steps The rate law of an elementary step is determined by its molecularity: –Unimolecular processes are first order, –Bimolecular processes are second order, and –Termolecular processes are third order. Rate Laws for Multistep Mechanisms Rate-determining step is the slowest of the elementary steps. Reaction Mechanisms

Rate Laws for Elementary Steps Reaction Mechanisms

Mechanisms with an Initial Fast Step 2NO(g) + Br 2 (g)  2NOBr(g) The experimentally determined rate law can be: d[NOBr]/dt = k obs [NO] 2 [Br 2 ] (or) = k obs’ [NO][Br 2 ] Consider the following mechanism Reaction Mechanisms

General Mechanism Overall Reaction: Proposed Mechanism: Where: D = observable product M = intermediate

Rate of reaction should be determine by change of concentration and pressure against time measure  P over time time Br 2 + HCOOH → 2Br - + 2H + + CO 2 2H 2 O 2 → 2H 2 O + O 2

14 Measurement of Reaction Rates Chemical Method The concentration of a reactant or product as a function of time Reaction vessels At constant T At intervals Slows down or stop the reaction Rapidly analyze chemical compositions of the mixture Cooling the sample removing a catalyst Diluting the mixture Adding a species

Reaction Rate and Stoichiometry For the reaction C 4 H 9 Cl(aq) + H 2 O(l)  C 4 H 9 OH(aq) + HCl(aq) we know In general for aA + bB  cC + dD Reaction Rates

C 4 H 9 Cl(aq) + H 2 O(l)  C 4 H 9 OH(aq) + HCl(aq)

Rate law

Rate of heterogeneous reaction depends on surface and concentrations of reagents in gas and sollution depends on surface and concentrations of reagents in gas and sollution : V = kSС СаО (т) + СО 2(г) = СаСО 3(т) V = kS пит. (СаО) С (СО 2 )

Background on Rates & Mechanisms Main Factors which influence reaction rate: – Concentrations of Reactants - Rates usually increase as reactant concentrations increase. – Reaction Temperature - An increase in temperature increases the rate of a reaction. – Presence of a Catalyst (not all rxns have catalysts) A catalyst is a substance which increases the rate of a reaction without being consumed in the overall reaction. The concentration of the catalyst or its surface area (if insoluble) are variables which influence the rate. Some catalysts are incredibly complex - like enzymes; and others are quite simple: H + + H 2 O + CH 2 = CH ) CH 3 -CH 2 -OH + H + – Type of Reactants – “Surface Area of Insoluble Reactant”

Exponents in the Rate Law For a general reaction with rate law we say the reaction is mth order in reactant 1 and nth order in reactant 2. The overall order of reaction is m + n + …. A reaction can be zeroth order if m, n, … are zero. Note the values of the exponents (orders) have to be determined experimentally. They are not simply related to stoichiometry. Concentration and Rate

First Order Reactions (to one component) The Change of Concentration with Time Isomeric Transformation of Methyl Isonitrile to Acetonitrile

23 First-Order Reactions Half-life: First-order reaction The time needed for [A] to drop to half its value Independent of [A] o A useful indication for the chemical reaction rate

Second Order Reactions The Change of Concentration with Time

Pseudo-Order Reaction Law

Integrated Rate Law - zero order

Summary of Rate Laws to One-Component First-OrderSecond-OrderZeroth-Order differential rate law (-dC/dt) kCkC 2 k Equation C = C o ·e -kt ln C = -kt + ln C o 1/C = kt + 1/C o C = -kt + C o Linear Equationln C vs. t1/C vs. tC vs. t Linear Plot Half-Lifeln(2)/k1/kC o C o /2k Units on ktime -1 M -1 time -1 M time -1 m = -k b = ln C o m = k b = 1/C o m = -k b = C o

IV.Determination of Order  Order - from units of k: If you are given the units of the rate constant for a reaction, then you will know the overall order (slide 14). Not too common.  Order by Method #1 - from altering M: Measure initial rates keeping one reactant constant and change the concentration of another; observe the rates; calculate order as illustrated in the next few slides.  Order by Method #2 - from integrated rate expression: Use calculus & integrate the rate expression between the limits of time = 0 & time = t. By plotting out the variables of these integrated rate expressions you can determine the order. This will be shown in the lecture, and you will be doing this in the kinetics lab.

Application in pharmacy Evaluation of drug stability of liquid dosage forms A typical plot of log rate constant as a function of pH for a drug (codeine sulfate) which undergoes both acid and base catalysis. Modifi ed from M.F. Powell, J.Pharm. Sci.75, 901