how can i control the rate of my reactions?

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How can I control the rate of my Reactions? Chemical Chemical Kinetics Kinetics Chapter 15 Chapter 15

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Chemical Kinetics Chapter 15. How can I control the rate of my Reactions?. Kinetics. Study of speed or rate of reactions. Chemical Kinetics. We can use thermodynamics to tell if a reaction is product or reactant favored . - PowerPoint PPT Presentation

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Page 1: How can I control the rate of my  Reactions?

How can I controlthe rate of my

Reactions?

Chemical Chemical KineticsKineticsChapter 15Chapter 15

Page 2: How can I control the rate of my  Reactions?

Kinetics•Study of

speed or rate of reactions.

Page 3: How can I control the rate of my  Reactions?

We can use thermodynamics to tell if a reaction is product or reactant favored.

But this gives us no info on HOW FAST reaction goes from reactants to products.

KINETICS — the study of REACTION RATES and their relation to the way the reaction

proceeds, i.e., its MECHANISM. The reaction mechanism is our goal!

We can use thermodynamics to tell if a reaction is product or reactant favored.

But this gives us no info on HOW FAST reaction goes from reactants to products.

KINETICS — the study of REACTION RATES and their relation to the way the reaction

proceeds, i.e., its MECHANISM. The reaction mechanism is our goal!

Page 4: How can I control the rate of my  Reactions?

Reaction rate = change in Reaction rate = change in concentration of a reactant concentration of a reactant or product with time.or product with time.

Three “types” of rates Three “types” of rates initial rateinitial rateaverage rateaverage rateinstantaneous rateinstantaneous rate

Reaction Rates Reaction Rates Section 15.1Section 15.1

Page 5: How can I control the rate of my  Reactions?

What is similar?

•ratio of two things

•TIME always Bottom !!!!!

Rate = [ x ] t

Change in amount

Change in time

Page 6: How can I control the rate of my  Reactions?

CALCULATING RATE

Page 7: How can I control the rate of my  Reactions?

RATE CALCULATIONS

1. John takes 10 weeks to earn $150. However, Mary earns $150 in 30 days. Calculate the rate at which they both earn money. Which has the larger rate?

Mary John Amount Amount

Time Time Rate ($/day) Rate ($/day)

Larger =

$150 $150

30 days 70 days

$5/day $2/day

Mary

Page 8: How can I control the rate of my  Reactions?

REACTION RATES ! !

RR = [reactants ] t

RR = [products ] t

Page 9: How can I control the rate of my  Reactions?

Blue dye is oxidized Blue dye is oxidized with bleach. with bleach.

Its concentration Its concentration decreases with time.decreases with time.

The rate — the change The rate — the change in dye conc with time in dye conc with time — can be determined — can be determined

from the plot.from the plot.

Blue dye is oxidized Blue dye is oxidized with bleach. with bleach.

Its concentration Its concentration decreases with time.decreases with time.

The rate — the change The rate — the change in dye conc with time in dye conc with time — can be determined — can be determined

from the plot.from the plot.

Dy

e C

on

ce

ntr

atio

nD

ye

Co

nc

en

trat

ion

Page 10: How can I control the rate of my  Reactions?
Page 11: How can I control the rate of my  Reactions?

REACTION RATES

RR = [P ] = - [R ] t t

P =products R = reactants

Page 12: How can I control the rate of my  Reactions?

Relative Rates

Reactant

2A 4B + C

- [A ] = [B ] = [C ] 2 t 4 t t

Page 13: How can I control the rate of my  Reactions?

Rate Expressions

Page 14: How can I control the rate of my  Reactions?

HOW CAN WE CHANGE REACTION RATES ?

• Some reactions need to be fast: airbags.

• Some reactions are slowed; time released pills

Examples:

Page 15: How can I control the rate of my  Reactions?

Collision Theory D9 C20

(theory about molecules colliding)

•Rate of reactions depend molecules colliding in such a way that old bonds break and new bonds form.

Page 16: How can I control the rate of my  Reactions?

COLLISION THEORY

•C = collisions

•E = energy

•O = orientation

Page 17: How can I control the rate of my  Reactions?

Factors Affecting RXN Rates

• Nature of Reactants

• Temperature• Concentration• Surface Area/ Physical

state• Catalysts

Page 18: How can I control the rate of my  Reactions?

Nature of Reactants

• What you use

Page 19: How can I control the rate of my  Reactions?

Nature of ReactantsExamples

•Packaging materials•Food•Building materials•Clothing •Fireworks

Page 20: How can I control the rate of my  Reactions?

Nature of ReactantsThe materials used

•Activation Energy; Unique to each substance

•Orientation of reactants; depends on reactants

Page 21: How can I control the rate of my  Reactions?

lower concentration of reactants More concentrated

Concentration (M)amount present

Page 22: How can I control the rate of my  Reactions?

Concentration (M)amount present

Examples

•Hydrogen peroxide•Food: vacuum packed•Breathing•Firemen

Page 23: How can I control the rate of my  Reactions?

0.3 M HCl0.3 M HCl

6.0 M HCl6.0 M HCl

ConcentrationsConcentrations

Page 24: How can I control the rate of my  Reactions?

Concentration (M)amount present

•Increasing the number of reactants, the chance of successful Collisions increase.

Page 25: How can I control the rate of my  Reactions?

Physical state Physical state of reactantof reactant

oror

Surface areaSurface area

Page 26: How can I control the rate of my  Reactions?

Surface AreaMore it can be spread out more area

Paper (demo)

MORE

kindle

groundLESS Whole bean

Logs

Page 27: How can I control the rate of my  Reactions?

SURFACE AREAamount in contact

Examples

•Fire: solid / liquid fuels •Food: chew or grinding•Brewing: tea or coffee•Grain elevator

Page 28: How can I control the rate of my  Reactions?

Surface Area•Number of particles that are exposed.

•More surface area = more reactions

•More contact = more Collisions.

Page 29: How can I control the rate of my  Reactions?

Temperature

• Increased temperature causes increased motion.

• Increases the KINETIC energy

Page 30: How can I control the rate of my  Reactions?

TEMPERATUREExamples

•Glowstick•Cook / freeze•Summer / winter•Ice pack / hot packs•Medication

Page 31: How can I control the rate of my  Reactions?

Temperature Temperature

Cold Hot

D9 C30

Page 32: How can I control the rate of my  Reactions?

Temperature

•Temperature is related to Kinetic Energy

Lower T has less E

•T: related to motionLower T = less motion

Collide less

Page 33: How can I control the rate of my  Reactions?

Collision Theory

Collisions

Collisions

EnergyCollisions

Energy

Orientation

NO

NO

YES

Page 34: How can I control the rate of my  Reactions?

Catalyst / Inhibitors•A substance NOT permanently changed during the reaction.

•Changes energy needed to start reaction

Page 35: How can I control the rate of my  Reactions?

Activation Energy

•Energy needed to start reaction

Page 36: How can I control the rate of my  Reactions?

Energy Diagram

Page 37: How can I control the rate of my  Reactions?

Catalyzed Reactions d9 c23

Page 38: How can I control the rate of my  Reactions?

Hydrogen peroxide Rxt.C34

Page 39: How can I control the rate of my  Reactions?

Catalyst•Works by changing the activation energy required

•The lower the Ea the greater the rate of the reaction.

Page 40: How can I control the rate of my  Reactions?
Page 41: How can I control the rate of my  Reactions?

Inhibitors d9 c38

•Works by changing the activation energy required

•The greater the Ea the lower the rate of the reaction.

Page 42: How can I control the rate of my  Reactions?

Energy Diagram

Inhibitors

Ea