Chemical Kinetics
Tro’s Chemistry Chapter 13 – Chemical Kinetics
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Acknowledgements: Many of the images are adopted from Tro’s textbook, the only purpose of which is to enhance student learning. Key terms, concepts, skills: Refer to pp 599 – 601. Review questions: 3 – 24. Suggested problems: 25, 27, 33, 39, 43, 53, 57, 59, 69, 73, 75, 81, 93, 103. 13.1 & 2 Introduction to the Rate of a Chemical Reaction • kinetics is the study of the factors that affect the speed of a reaction and the mechanism by which a reaction proceeds. • experimentally it is shown that there are 4 factors that influence the speed of a reaction: nature of the reactants, temperature catalysts concentration • • rate of a chemical reaction is generally measured in terms of how much the concentration of a reactant decreases in a given period of time or product concentration increases for reactants, a negative sign is placed in front of the definition
• •
as time goes on, the rate of a reaction generally slows down because the concentration of the reactants decreases. at some time the reaction stops, either because the reactants run out or because the system has reached equilibrium.
Reaction Rate and Stoichiometry • in most reactions, the coefficients of the balanced equation are not all the same H2(g) + I2(g) → 2 HI(g) • for the above reaction, for every 1 mole of H2 used, 1 mole of I2 will also be used and 2 moles of HI made, therefore the rate of change will be different • in order to be consistent, the change in the concentration of each substance is multiplied by 1/coefficient ∆[H 2 ] ∆[I 2 ] ⎛ 1 ⎞ ∆[HI] Rate = − =− = +⎜ ⎟ ∆t ∆t ⎝ 2 ⎠ ∆t • the average rate is the change in measured concentrations in any particular time period, linear approximation of a curve • the larger the time interval, the more the average rate deviates from the instantaneous rate • the instantaneous rate is the change in concentration at any one particular time, i.e., the slope at a given point of the curve •
Page 1 of 13
Acknowledgements: Many of the images are adopted from Tro’s textbook, the only purpose of which is to enhance student learning. Key terms, concepts, skills: Refer to pp 599 – 601. Review questions: 3 – 24. Suggested problems: 25, 27, 33, 39, 43, 53, 57, 59, 69, 73, 75, 81, 93, 103. 13.1 & 2 Introduction to the Rate of a Chemical Reaction • kinetics is the study of the factors that affect the speed of a reaction and the mechanism by which a reaction proceeds. • experimentally it is shown that there are 4 factors that influence the speed of a reaction: nature of the reactants, temperature catalysts concentration • • rate of a chemical reaction is generally measured in terms of how much the concentration of a reactant decreases in a given period of time or product concentration increases for reactants, a negative sign is placed in front of the definition
• •
as time goes on, the rate of a reaction generally slows down because the concentration of the reactants decreases. at some time the reaction stops, either because the reactants run out or because the system has reached equilibrium.
Reaction Rate and Stoichiometry • in most reactions, the coefficients of the balanced equation are not all the same H2(g) + I2(g) → 2 HI(g) • for the above reaction, for every 1 mole of H2 used, 1 mole of I2 will also be used and 2 moles of HI made, therefore the rate of change will be different • in order to be consistent, the change in the concentration of each substance is multiplied by 1/coefficient ∆[H 2 ] ∆[I 2 ] ⎛ 1 ⎞ ∆[HI] Rate = − =− = +⎜ ⎟ ∆t ∆t ⎝ 2 ⎠ ∆t • the average rate is the change in measured concentrations in any particular time period, linear approximation of a curve • the larger the time interval, the more the average rate deviates from the instantaneous rate • the instantaneous rate is the change in concentration at any one particular time, i.e., the slope at a given point of the curve •