Kinetics

Chapter 12

Chemistry

SC5

Think About It

• Rank in order from slowest to fastest chance of causing an automobile accident.– Option A: A person obeying all the traffic laws– Option B: A person changing the radio station

in the car.– Option C: A person changing the radio station

and making a phone call in the car.– Option D: A person changing the radio station,

making a phone call and drinking water.

What Is a Reaction Rate?• Measures the change in

concentration of a substance over time.–Concentration: moles in a liter (M)

• Concentration of A is written as [A]–Units: mol/L x s

What Is the Formula of Average Rate?

• Average Rate = Δ [reactant] / Δ time• Average Rate = concentrationfinal – concentrationinitial

• timefinal – timeinitial

Practice 1 Average Rate

• What is the average rate in a reaction between butyl chloride (C4H9Cl) and water, if the concentration of C4H9Cl is 0.220 M at the beginning and after 4.00 s the concentration of C4H9Cl is 0.100 M?

Practice Problems – Classwork/Homework

Red Cards• P. 563 – Practice

Problems• Problem 1

Black Cards• P. 563 – Practice

Problems• Problem 2

Homework

Chapter 16• P. 586 #48

– Careful, go to moles!

Storyboarding Collision Theory

• To understand reactions you have to be able to ‘see’ it at the molecular level. Picture it and all the theories make sense.

• Activity: You are being given a colorful sheet of paper. You will storyboard the Collision Theory as it appears p. 563-565 in textbook.– Requirements:

• Must have all three postulates.• Must have original wording of the postulate.• Must have your interpretation of the each postulate.• Must have a visual representation of each postulate.• Must have a summary box on its own (sentence combining).

Storyboarding Collision Theory

• Rubric:– Requirements:

• Must have all three postulates. _____/10• Must have original wording of the postulate. ___/10• Must have your interpretation of the each postulate. ___/10• Must have a visual representation of each postulate. ___/10• Must have a summary box on its own (sentence combining).

___/10• Verbal Explanation ____/30• Visually Pleasing ____/10• Neatness/Colorful ____/10• Total = ____/100• Plagiarism from the book is a grade of 0 and you will have to

redo.

ABC of Collision TheoryMy Storyboard

• All three of these postulates affect the rate of the reaction because the reactants have to– Attack each other hard

(correct energy)– Be aligned properly

(hit on correct side)– Collide (find each

other)

Storyboarding Collision Theory

• Rubric:– Requirements:

• Must have all three postulates. _____/10• Must have original wording of the postulate. ___/10• Must have your interpretation of the each postulate. ___/10• Must have a visual representation of each postulate. ___/10• Must have a summary box on its own (sentence combining).

___/10• Verbal Explanation ____/30• Visually Pleasing ____/10• Neatness/Colorful ____/10• Total = ____/100• Plagiarism from the book is a grade of 0 and you will have to

redo.

Collision Theory

1.Collision • For a reaction to occur they reactants must collide.

Collision Theory

2.Activation Energy

• For a reaction to occur you must have sufficient energy.

Collision Theory

3.Orientation • For a reaction to occur, you must have correct alignment.

Collision Theory

• Youtube: Collision Theory• http://www.youtube.com/watch?v=xswUKlUSsc0

– Collision– Activation Energy– Orientation

Going Further with Collision Theory

Homework• P. 586 (52, 54, 55)

52. Apply collision theory to explain why the increasing concentration of a reactant usually increases the reaction rate.

54. Food Preservation Apply collision theory to explain why foods usually spoil more slowly when refrigerated than at room temperature.

55. Apply collision theory to explain why powdered zinc reacts to form hydrogen gas faster than large pieces of zinc when both are placed in hydrochloric acid solution.

Factors Affecting Reaction Rates

• A reaction can increase in rate (speed) or decrease in speed only by these factors.– Catalyst– Concentration– Nature of the reactant– Pressure– Surface Area– Temperature

• That means stirring does NOT increase the rate of the reaction.

Factors Affecting Reaction Rates

• Nature of the reactant– Is the reactant naturally

reactive?– More unstable the more

reactive it is.• Cs and F are very reactive.

– Decreases activation energy which makes forming the activated complex easier.

Activation EnergyEa – get into the game!

Type of reactant decreases the activation energy.

Reaction Pathway

Ene

rgy

Reactants

Products

before

after

Factors Affecting Reaction Rates

• Concentration– The more of the

reactant present, the higher the number of collisions.

– Particles bump more if there are more there.

Factors Affecting Reaction Rates

• Surface Area– The more parts the reactant can collide with the

higher the reaction rate.• This increases the amount of collisions.

Factors Affecting Reaction Rates

• Temperature– The higher the

temperature, the faster the particles move which increase the number of collisions.• This increases

collisions, good orientation and gives a higher energy.

Reaction Rates - Demonstration

• H2O2 will decompose over time.

2 H2O2 2 H2O + O2

Reaction Rates - Demonstration

Group As• You have a cup of hydrogen peroxide that is

decomposing, observe the reaction and explain what you observe.– THINK: are there bubbles, is there a smell, does anything

change, how long does it take, identify the product.– What can make this reaction go faster?

Reaction Rates - Demonstration

Group Bs• You have a cup of hydrogen peroxide that is decomposing,

observe the reaction and explain what you observe.– THINK: are there bubbles, is there a smell, does anything change, how

long does it take, identify the product.– Identify if the yeast is a reactant or catalyst.– What is the difference between reactant and catalyst?– Why did the reaction occur so quickly?

Learning About Catalyst

• What is the purpose of a catalyst in a reaction?

• Does the catalyst react and form an new product?

• To speed up a reaction by orienting the particles properly (glue)

• A catalyst is just there to hold two pieces together, it does not form a new product.

Going Further with Collision Theory

Homework• p. 586 (50, 51, 53, 56)

50. What role does reactivity of the reactants play in determining the rate of a chemical reaction?

51. In general, what is the relationship between reaction rate and reaction concentration?

53. Explain why a crushed solid reacts with a gas more quickly than a large chunk of the same solid.

56. Hydrogen peroxide decomposes to water and oxygen gas more rapidly when manganese dioxide is added. The manganese dioxide is not consumed in the reaction. Explain the role of manganese dioxide.

Activation Energy• A major requirement for all REACTIONS to occur. • Get over the ‘hump’ to form products

Activation EnergyEa – get into the game!

Type of reactant decreases the activation energy.

Reaction Pathway

Ene

rgy

Reactants

Products

before

after

Activation EnergyEa – get into the game!

Reaction Pathway

Reaction Pathway – the direction of the reaction from the beginning to the end. Reaction from reactant to product.

Activation EnergyEa – get into the game!

Energy – how much energy is needed to complete the reaction. (q=mc(Tf - Ti)).

Reaction Pathway

Ene

rgy

Activation EnergyEa – get into the game!

Reaction Pathway

Ene

rgy

Reactants

Just before the reaction begins, the energy needed to collide particles.

Ea

Activation EnergyEa – get into the game!

The particles are colliding, aligned properly and finally hitting enough energy to form this intermediate.

Reaction Pathway

Ene

rgy

Reactants

Activated Complex

Ea

Activation EnergyEa – get into the game!

If the product is below the reactant, energy is released. This is an exothermic reaction. Usually, exothermic reactions feel warm or do work.

Reaction Pathway

Ene

rgy

Reactants

Activated Complex

Products

Ea

-ΔE

Activation EnergyEa – get into the game!

If the product is above the reactant, energy is absorbed. This is an endothermic reaction. Usually, endothermic reactions feel cold or require work.

Reaction Pathway

Ene

rgy

Activated Complex

Reactants

Products

Ea

+ΔE

Let Them Eat Cake Pudding

1. Following the recipe but using HALF the ingredients (except batter).

2. Following the recipe exactly.

3. Following the recipe but using DOUBLE the ingredients (except batter)

– Predict what you think will happen and WHY? Which factors will affect the rate of the reaction?

We are going to make three concentrations of puddings

Formal Lab Write UpDue a week from today.

Look over rubric

Rate Law

• Because of the nature of the reactant, there is a way to formulate a mathematical expression based on reaction and the concentration of the reactants.

aA bB• The rate law for the above BALANCED chemical

reaction is Rate = k[A]m. – General rate law have a constant, k whose units change

depending on the order.– Exponent m tells you how reactive the reactant is.

Rate Law - Practice• Use the reactants below to write the rate law:

aA + bB cC– Answer:

Remember, you don’t know the superscript so use a variable.

Rate Law - Practice• Use the reactants below to write the rate law:

aAB + bB cC– Answer:

Remember, you don’t know the superscript so use a variable.

Zero Order

• If the concentration of a reactant doubles but the rate does nothing, the reaction is zero order.

• Write the rate law as Rate = k[B]0

Rate = k x 1

Rate = k

Practice Rate Law 1

Trial Initial [A], M Initial Rate (mol/L s)1 0.100 2.00 x 10-3

2 0.200 2.00 x 10-3

• What happen to the [A]?– A. did not change B. doubled C. I don’t know

• What happen to the rate?– A. did not change B. doubled C. I don’t know

• What order is this reaction?

First Order Reactant

• A reaction is first order if the concentration of ONE reactant doubles and the rate doubles.– Write the law as

•Rate = k[A]1 •Rate = k[A]

– k is just a constant that can be solved (unit is 1/s or s-1).– m = 1 to reflect the ‘1st’ order.

Practice Rate Law 1

Trial Initial [B], M Initial Rate (mol/L s)1 0.100 2.00 x 10-3

2 0.200 4.00 x 10-3

• What happen to the [B]?– A. did not change B. doubled C. I don’t know

• What happen to the rate?– A. did not change B. doubled C. I don’t know

• What order is this reaction?

Combine Rate Laws

• The overall order of reaction is:– The sum of the exponents in the rate law.

• For example

–Rate = k[A]0[B]1

• The overall reaction of the above is first order (0+1 = 1).

Overall Rate Law Problem 1:

• NH4+ (aq) + NO2

- (aq) N2 (g) + 2 H2O (l)– Find the rate law

Experiment # Initial [NH4+] Initial [NO2

-] Rate (M/s)

1 0.0100 0.200 5.4x10-7

2 0.0200 0.200 10.8x10-7

3 0.0400 0.200 21.5x10-7

4 0.200 0.0202 10.8x10-7

5 0.200 0.0404 21.6x10-7

6 0.200 0.0808 43.3x10-7

Problem 1: Answers

• NH4+ (aq) + NO2

- (aq) N2 (g) + 2 H2O (l)– [NH4

+] doubles; Rate doubles = first order

– [NO2-] doubles; Rate doubles = first order

– Rate Law: Rate = k[NH4+][NO2

-]

Experiment # Initial [NH4+] Initial [NO2

-] Rate (M/s)

1 0.0100 0.200 5.4x10-7

2 0.0200 0.200 10.8x10-7

3 0.0400 0.200 21.5x10-7

4 0.200 0.0202 10.8x10-7

5 0.200 0.0404 21.6x10-7

6 0.200 0.0808 43.3x10-7

Homework

Homework, read the section 16.3.• Write down keywords you don’t understand.• Write down questions you had on the reading.• Write down questions you have on the math.• Problems p. 587 #66 (try #67)

Rate Determining Steps

• To calculate the rate, you must look at the SLOWEST step. Label it as the rate determining step.– Ex 1: 2A product (slow)

• Rate = k[A]2

– Ex 2: 2A + B product (slow)• Rate = k[A]2[B]

Which Is the Rate determining Step?

• Step 1: O3 + NO NO2 + O2 (slow)

• Step 2: NO2 + O NO + O2 (fast)

STEP 1

Which Is the Rate determining Step?

• Step 1: H2O2 + I- H2O + IO- (slow)

• Step 2: H2O2 + IO- H2O + O2 + I- (fast)

STEP 1

Which Is the Rate determining Step?

• Step 1: HBr + O2 HOOBr (slow)

• Step 2: HBr + HOOBr 2 HOBr (fast)• Step 3: 2 HBr + 2 HOBr 2 H2O + 2 Br2 (fast)

STEP 1

Homework

• Chapter 16.4– Problems 69, 70, 71, 72

Terms of Endearment Frayer Model

• Homogeneous catalyst• Activated complex• Activation energy• Average reaction rate• Catalyst• Collision Theory• Endothermic• Exothermic

• Heterogeneous catalyst

• Intermediate• Rate law• Rate-determining step• Reaction rate• Reaction mechanism• Reaction order• Spontaneity

PollEverywhere Questions

www.polleverywhere.com

In the "Collision Theory" students learn that a reaction requires THREE

postulates/main ideas. Which is not ONE of those postulates?

• Text to number: 37607

Answers (put in message)• Activation Energy - 602348• Activated Complex - 602349• Catalyst - 602350• Collisions - 602351