1. Unit 7 Test = ___% 2. I studied by … 3. Next time I will study by… 4. We will reevaluate our goals momentarily… Day period 3

4. Reevaluating your goal:  Calculate your average on the 7 tests we’ve taken (use your tests or your goal setting ATBs to get grades).  Record your average. Test average so far = ____  Record your new goal (you must improve upon your average by at least 2 percentage points (or one if your average is an A)). Day period 3

1. Unit 7 Test = ___% 2. I studied by … 3. Next time I will study by… 4. We will reevaluate our goals momentarily… Day period 1

4. Reevaluating your goal:  Calculate your average on the 7 tests we’ve taken (use your tests or your goal setting ATBs to get grades).  Record your average. Test average so far = ____  Record your new goal (you must improve upon your average by at least 2 percentage points (or one if your average is an A)). Day period 1

Question of the Day ΔG determines whether or not a reaction will _____, but even a spontaneous reaction can be very _________. Day pd 3 GO SLOW

Objective How fast / slow do reactions go?

Reaction Rates Intro. to Rxn Rates & Collision Theory:  Rates of reaction determine how fast a reaction goes.  Usually expressed as the change in amount of reactant or product per unit time (moles / unit time)

Reaction Rates Collision Theory: = atoms, ions, and molecules can react to form products, if and only if, they collide with enough kinetic energy. If they do not have enough kinetic energy to react they bounce apart unchanged.

Reaction Rates Collision Theory: The minimum energy that colliding particles must have to react is called activation energy.

Reaction Rates

Factors Affecting Rxn Rates: 1. Temperature  at higher temps. particles move faster and so frequency of collisions increases along with the kinetic energy of particles… activation energy overcome easier

Reaction Rates Factors Affecting Rxn Rates: 2. Concentration  increasing concentration increases frequency of collision… activation energy overcome easier

Reaction Rates Factors Affecting Rxn Rates: 3. Particle size  smaller particle size = greater surface area and so more reactant available for reaction so frequency of collisions increases… activation energy overcome easier

Reaction Rates Factors Affecting Rxn Rates: 4. Catalyst  catalyst = a substance that speeds up the rate of reaction without being changed itself  a catalyst speeds up the reaction by helping the reactants reach their activated complex (by decreasing the needed activation energy)

Reaction Rates Factors Affecting Rxn Rates: 4. Catalyst  A catalyst is not changed during reaction, therefore it is NOT written as a reactant or product, but usually over the yield arrow: 2H 2(g) + O 2(g) 2H 2 O (g) Pt

Reaction Rates

II. The Progress of Chemical Reactions: A.Chemical kinetics is the study of the rates of chemical reactions: How fast will the reaction go? B.Reaction rate is the change in concentration of reactant or product over time.

Reaction Rates II.The Progress of Chemical Reactions: B.Reaction rate is the change in concentration of reactant or product over time. 1.Rxn rate CANNOT be determined by just looking at the chemical equation. 2.Formula:

Reaction Rates 1.Rxn rate CANNOT be determined by just looking at the chemical equation. 2.Formula: [ ] = concentration = M =moles/L

Question of the Day Four factors that influence reaction rate = … Day

Assignment Read / review section 18.1 and complete #s 1-5 on page 601.

Reaction Rates II.The Progress of Chemical Reactions: C. Rate Laws  rate law = an expression for the rate of a reaction in terms of the concentrations of reactants

Reaction Rates II.The Progress of Chemical Reactions: NOTE: k is large if the products form quickly and small if the products form slowly.

Reaction Rates II.The Progress of Chemical Reactions: Reaction order from rate laws: Rates can depend on different reactants in different ways. If :x = 0 – the reaction is said to be zero order in reactant 1 and the rate of reaction is independent of the concentration of reactant 1

Reaction Rates II.The Progress of Chemical Reactions: x = 1 – the reaction is said to be first order in reactant 1 and the rate is directly related to the concentration of reactant 1 x = 2 – the reaction is said to be second order in reactant 1 and the rate is dependent on the concentration of reactant 1 squared.

Reaction Rates II.The Progress of Chemical Reactions: Note: the overall order for a reaction is simply the individual orders for each reactant added together (a reaction that is first order in A and second order in B is third order overall).

Reaction Rates II.The Progress of Chemical Reactions: Note: the overall order for a reaction is simply the individual orders for each reactant added together (a reaction that is first order in A and second order in B is third order overall). formula to find order:

Reaction Rates Example: Consider the rxn A  B. The rate law for this rxn is rate = k[A] x. From the data below, find the order of the rxn w/ respect to A and the overall order of the rxn. TRIALINITIAL CONCENTRATION OF A (mol/L) INITIAL RATE (mol/(L*s)) * * * 10 -4

Reaction Rates How about units for k?  units for k depend on the order of the reaction  units for the rate = concentration / time = M/s = mols/(L*s) What would the units for k be if the reaction was first order overall?

Reaction Rates EXAMPLE: The following data were collected for the rate of disappearance of NO in the reaction: 2NO(g) + O 2 (g)  2NO 2 (g) Initial Rate Experiment What is the rate law for the reaction and the value of the rate constant? Experiment Number [NO] (M)[O 2 ] (M) initial rate (M/s) x x x 10 -2

Question of the Day Day The data in the table below were obtained for the rxn: a. The order of the reaction in A is ____. b. The order of the reaction in B is ____. c. The overall order of the reaction is ____

Reaction Rates The reaction 2NO + 2H 2  N 2 + 2H 2 O is first-order in H 2 and second-order in NO. What happens to the rate when (i) [NO] is doubled, while [H 2 ] is fixed (ii) [NO] is fixed, while [H 2 ] is doubled (iii) both [NO] and [H 2 ] are doubled? quadruples doubles X 8

Review Suppose that for the reaction A + B → C, the rate law is rate = 3.0 x [A][B] 2. What is the concentration of “B” if [A] = 0.10 M and the rate is 1.2 x M/s? There are no units on k, what should they be? M

Rxn Mechanisms & Rate-Determining Steps A.A reaction mechanism is a series of ____________ that lead to a net reaction. B.Reaction mechanisms can have _____________ steps. C.Parts of mechanisms 1.Net reaction is _________ simple rxns one or more the goal

Rxn Mechanisms & Rate-Determining Steps C.Parts of mechanisms 1.Net reaction is __________ 2.Elementary step is one of the __________ in the ________ 3.Intermediate product is a product that is made by _______________ _____ that becomes a _________ in a subsequent ________________ the goal reactionsprocess an elementary step reactant elementary step

Rxn Mechanisms & Rate-Determining Steps C.Parts of mechanisms 4.Catalyst is a substance that first appears as a _________ in one ________________ and then becomes a ________ in a subsequent ________________ reactant elementary step product elementary step

Reaction mechanisms that have multiple steps have one step that is the rate-determining step. The rate- determining step is the step that is the _______ of all the steps. Rxn Mechanisms & Rate-Determining Steps slowest

/esm_brown_chemistry_ 9/2/660/ cw/inde x.html Homework # 2 Chapter 14 – w/ discussion partner – show me successful screen (100%) # 7 = the reaction rate would quadruple.  doubling the partial pressure is the same as doubling the concentration.

Rate = k[A] x [B] y Average Rate of Reaction = Δ[reactant] ΔtΔt OR Δ[product] ΔtΔt [ ] = concentration = M = moles solute liters solution Average Rate of Reaction = OR [ ] = = M =

Rate = k[reactant 1 ] x [reactant 2 ] y Average Rate of Reaction = Δ[reactant] ΔtΔt OR Δ[product] ΔtΔt [ ] = concentration = M = moles solute liters solution [ ] = = M = generic rate law k = rate constant – temp. sensitive x, y = order of rxn – how Δ[ ] affects rate – found through experimentation

rate new rate old = conc new conc old ( ) x liters solution [ ] = = M = A B