KINETICS How Fast Does It Go? TEST REVIEW

CONTEXT CLUES ABOUT ORDER Given successive half-lives 1. Each successive half-life is SAME ln [A] = - kt + ln [A] 0

CONTEXT CLUES ABOUT ORDER Given successive half-lives 2. Each successive half-life DOUBLES

CONTEXT CLUES ABOUT ORDER Given successive half-lives 3. Each successive half-life HALVE

CONTEXT CLUES ABOUT ORDER

AP QUESTION 1 What is the activation energy for the reverse reaction?

Complete the graph that represents the change in N 2 O 5 concentration over time as the reaction proceeds.

B ( ii ) Describe how the graph in part b(i) could be used to find the reaction rate at a given time, t.

What data would you plot to test (a) zero order reaction rate? [A] time Slope = ? -k

What data would you plot to test (b) First order reaction rate? ln[A] time Slope = ?

What data would you plot to test (c) Second order reaction rate? time Slope = ? k

MULTIPLE CHOICE STRATEGIES Use Easy Math A + B  C Based on the following experimental data, what is the rate law for the hypothetical reaction given above? Experiment[A] (mol/L)[B] (mol/L)Initial Rate of formation of C (mol/ L∙ s) x x x Rate = k[B]

MULTIPLE CHOICE STRATEGIES Use Easy Math The concentration of A was measured periodically and recorded in the chart above. Based on the data in the chart, which of the following is the rate law for the reaction? Time ( hours)[A] (mol/L) Successive half-lives are constant so… Rate = k[A]

MULTIPLE CHOICE STRATEGIES A multistep reaction takes place by the following mechanism: A + B  C + D A + C  D + E Which of the species shown above is an intermediate in the reaction? (A) A(B) B (C) C(D) D

MULTIPLE CHOICE STRATEGIES The reaction below takes place with all of the reactants and products in the gaseous phase. Which of the following is true of the relative rates of disappearance of the reactants and appearance of the products? 2 NOCl  2 NO + Cl 2 (A)NO appears at twice the rate that NOCl disappears (B)NO appears at the same rate that Cl 2 appears (C)Cl 2 appears at the same rate that NOCl disappears (D) NO appears at the same rate that NOCl disappears

RELATIVE RATES Compare the rate of disappearance of N 2 to each compound shown in the reaction below. N 2 (g) + 3H 2 (g)  2 NH 3 (g) N 2 disappears half as fast as Cl 2 appears.

RELATIVE RATES

FACTORS THAT AFFECT THE RATE OF A REACTION Concentration of reactants -More molecules moving around, more collisions Big Idea: Particles must collide for reaction to occur

FACTORS THAT AFFECT THE RATE OF A REACTION Pressure Increases - more collisions Big Idea: Particles must collide with proper orientation Most often only two particles may collide at one time

FACTORS THAT AFFECT THE RATE OF A REACTION Reaction rate increases with Increasing temperature. KE avg increases with temperature so the molecules are moving faster and collisions are more energetic and more frequent! A general rule of thumb is that reaction rate doubles for each 10 ⁰ C rise in temperature! Big Idea: Particles must collide with minimum energy to be productive.

FACTORS THAT AFFECT THE RATE OF A REACTION Nature of reactants Big Idea: Solutions react quickly; opposite charged ions react quickly; stronger bonds in reactants slows rate; more bonds in reactants slows rate; solids react more slowly than liquids or solutions

FACTORS THAT AFFECT THE RATE OF A REACTION Increasing the surface area speeds up a reaction Big Idea: Excluding gas phase reactions and solutions, reactions occur at the boundary between phases so the more exposed area the more collisions. Example : Fine powders are fire hazards Coal dust vs. charcoal Dust, lint from dryers is #1 cause of house fires

FACTORS THAT AFFECT THE RATE OF A REACTION Catalyst Changes reaction pathway or mechanism which lowers E activation Big Idea: Activated Complex Is at top of hill. Reaction can go either way

MECHANISMS Intermediate(s): Catalyst: Overall Reaction =