Thermodynamics - PowerPoint PPT Presentation

About This Presentation
Title:

Thermodynamics

Description:

Thermodynamics Tells if a reaction will occur – PowerPoint PPT presentation

Number of Views:438
Avg rating:3.0/5.0
Slides: 39
Provided by: wappin63
Category:

less

Transcript and Presenter's Notes

Title: Thermodynamics


1
Thermodynamics
  • Tells if a reaction
  • will occur

2
Kinetics
  • Tells how fast a reaction will occur

3
Reaction Rate
  • Speed of the reaction
  • Found experimentally
  • Measure change in concentration of reactant or
    product over time
  • Rate ?Concentration
  • ?time

4
How do you measure rates?
  • Measure concentration of 1 or more
    reactants/products over time
  • Reactants disappear
  • Products appear
  • reaction rate change in concentration of
    reactants products in given amount time

5
Concentration of Reactants, Products
Appearance of products
Disappearance of reactants
6
How do reactions occur?
  • Must have an effective collision between reacting
    particles
  • Collision Theory
  • Collision must be energetic
  • Collision must occur at an effective angle

7
Particle Diagram of Collision
8
Reaction Rates depend on
  • frequency of collisions
  • how often occur
  • And
  • efficiency of collisions
  • what percentage are effective

9
Collision Theory
  • Molecules must collide in order to react
  • Effective collisions lead to formation of
    products
  • Ineffective collisions do not lead to products

10
Effective Collisions
  • Energetic
  • Favorable Orientation

11
Effective vs. Ineffective Collision
12
Most collisions are NOT effective!
13
Why Do Collisions Have to be Energetic?
14
Activation Energy Reaction
15
Energy Diagram of a Reaction
16
Activation Energy
  • Energy needed to initiate reaction
  • Energy needed to overcome reaction barrier
  • difference between where reactants start top
    of hill
  • Difference between reactants activated complex

17
Activation Energy
  • Using match to start a fire
  • spark plug in car engine

18
Potential Energy Curve Endothermic
Endothermic Reaction Products have more P.E.
than reactants Start low, end high
19
Potential Energy Curve Exothermic
Exothermic Reaction Products have less P.E.
than reactants Start high, end low
20
Have to label 6 energies on curve reactants
products
Both endo exo reactions
21
6 Energies to Label
Label on both endo exo P.E. curves
  1. PE reactants
  2. PE products
  3. PE activated complex
  4. Ea forward reaction
  5. Ea reverse reaction
  6. ?H

22
Ea for reverse rxn
Ea for forward rxn
P.E. of activated complex
P.E. of products
23
?H of reaction
24
P.E. of reactants
P.E. of activated complex
P.E. of products
Time What kind
of reaction is represented?
25
?H of reaction
26
Why does collision have to be energetic?
  • kinetic energy(KE) of reactants is used to
    overcome reaction barrier
  • KE is transformed into PE

27
Factors that determine reaction rates
  1. Nature of reactants (ions vs molecules)
  2. Temperature
  3. Concentration
  4. Pressure (gases only)
  5. Surface Area
  6. presence of catalyst

28
Nature of the reactantsIons or Molecules?
  • Ions in solution react quickly
  • Covalently bonded molecules react slowly
  • takes time to break all those bonds!
  • 2 gas phase reactants react more quickly than 2
    liquids or 2 solids

29
Temperature
  • measure of average KE of molecules in system
  • faster molecules are moving, will collide more
    often
  • faster molecules are moving, more energetic the
    collisions

30
Increase in Temperature
  • Increases frequency of collisions
  • Increases percentage of collisions that lead to
    reaction

31
Concentration
  • Increase in concentration
  • more particles per unit volume
  • more collisions in given amount time

32
Pressure
  • systems involving gases changing pressure
    analogous to changing concentration
  • ? Pressure, ? particles per unit volume
  • ? Pressure, ? particles per unit volume

33
Surface Area
  • Higher surface area
  • more particles exposed for reaction
  • Higher surface area means smaller particle size
  • (For heterogeneous reactions)

34
Vocabulary Interlude
  • Homogeneous Reaction
  • all reactants in same phase
  • Heterogeneous Reaction
  • reactants in different phases

35
Catalyst
  • Substance that increases rate of reaction without
    itself being consumed
  • does not participate in reaction
  • Provides alternate reaction pathway with lower
    energy barrier

36
(No Transcript)
37
Reaction Mechanism
  • series of steps that leads from reactants to
    products
  • describes how bonds break, atoms rearrange, and
    bonds form in reaction

38
Elementary Step
  • each individual step in reaction mechanism
  • lowest elementary step called
  • rate-determining step
Write a Comment
User Comments (0)
About PowerShow.com