factors affecting reactions chapter 14. chemical kinetics area of chemistry involved with the...
TRANSCRIPT
![Page 1: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/1.jpg)
Factors Affecting Reactions
Chapter 14
![Page 2: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/2.jpg)
Chemical Kinetics
• Area of chemistry involved with the speeds, or rates, of chemical reactions– How fast can reactants be converted to
products• Reaction rate= the change in the concentration
(measured in molarity) divided by the time interval– The longer the reaction takes, the slower the rate
![Page 3: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/3.jpg)
Factors that Affect Reaction Rate
1. Concentration– In most reactions, as concentration
increases, the frequency at which molecules collide increases.
![Page 4: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/4.jpg)
Beer’s Law
• Spectroscopic determination of concentration using absorbance of light can be used to tell how a concentration changes over time
![Page 5: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/5.jpg)
2. Temperature
• Generally, as temperature increases, so does the reaction rate.
• Increasing the T increases the avg. KE of the molecules which would makes molecules move and collide more frequently
![Page 6: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/6.jpg)
3. Physical State of the Reactants
• Reactants must come together to react in the correct orientation (right parts of molecules must collide)
• Reactions are limited by the area of contact between colliding particles– Increasing surface area, increases the rate of
the reaction
![Page 7: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/7.jpg)
The Collision Model
– In a chemical reaction, bonds are broken and new bonds are formed.
– Molecules can only react if they collide with each other.
– Furthermore, molecules must collide with the correct orientation and with enough energy to cause bond breakage and formation.
![Page 8: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/8.jpg)
Activation Energy• In other words, there is a minimum amount of energy
required for reaction: the activation energy, Ea.
• Just as a ball cannot get over a hill if it does not roll up the hill with enough energy, a reaction cannot occur unless the molecules possess sufficient energy to get over the activation energy barrier.
![Page 9: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/9.jpg)
Reaction Coordinate Diagrams
It is helpful to visualize energy changes throughout a process on a reaction coordinate diagram like this one for the rearrangement of methyl isonitrile.
![Page 10: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/10.jpg)
Reaction Coordinate Diagrams• It shows the energy of
the reactants and products (and, therefore, E).
• The high point on the diagram is the transition state.
• The species present at the transition state is called the activated complex.
• The energy gap between the reactants and the activated complex is the activation energy barrier.
![Page 11: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/11.jpg)
Maxwell–Boltzmann Distributions
• Temperature is defined as a measure of the average kinetic energy of the molecules in a sample.
• At any temperature there is a wide distribution of kinetic energies.
![Page 12: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/12.jpg)
Maxwell–Boltzmann Distributions
• As the temperature increases, the curve flattens and broadens.
• Thus at higher temperatures, a larger population of molecules has higher energy.
![Page 13: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/13.jpg)
Maxwell–Boltzmann Distributions
• If the dotted line represents the activation energy, as the temperature increases, so does the fraction of molecules that can overcome the activation energy barrier.
• As a result, the reaction rate increases.
![Page 14: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/14.jpg)
Maxwell–Boltzmann Distributions
This fraction of molecules can be found through the expression
where R is the gas constant and T is the Kelvin temperature.
f = e−Ea/RT
![Page 15: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/15.jpg)
Arrhenius Equation
Svante Arrhenius developed a mathematical relationship between k (rate constant) and Ea (Activation Energy):
k = A e−Ea/RT
where A is the frequency factor, a number that represents the likelihood that collisions would occur with the proper orientation for reaction.
![Page 16: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/16.jpg)
Arrhenius Equation
• k = A e−Ea/RT
– Rate increases as activation energy is decreased
– Rate increases as temperature increases
![Page 17: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/17.jpg)
4. Catalysts• Catalysts increase the rate of a reaction by
decreasing the activation energy of the reaction.
• Catalysts change the mechanism by which the process occurs.
![Page 18: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/18.jpg)
CatalystsOne way a catalyst can speed up a reaction is by holding the reactants together and helping bonds to break.
![Page 19: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/19.jpg)
Enzymes• Enzymes are catalysts in
biological systems.• The substrate fits into the
active site of the enzyme much like a key fits into a lock.– Fits because of intermolecular
forces between reactants and enzyme
– Lowers the activation energy– Or creates new reaction
intermediates
![Page 20: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/20.jpg)
Function of Enzymes
• Since many enzymes are large biomolecules, the intermolecular forces within it impact it’s functionality
• Enzymes must be in correct shape to work correctly– Noncovalent interactions (hydrogen bonds,
dispersion, dipole-dipole forces) impact shape and how well an enzyme can increase chemical reaction rates
![Page 21: Factors Affecting Reactions Chapter 14. Chemical Kinetics Area of chemistry involved with the speeds, or rates, of chemical reactions –How fast can reactants](https://reader033.vdocuments.mx/reader033/viewer/2022052414/56649d745503460f94a53731/html5/thumbnails/21.jpg)
Other forms of catalysis
• Acid-base catalysis– Reactant either gains or loses a proton,
changing the rate of the reaction
• Surface catalysis– Either a new reaction intermediate is formed,
or the probability of successful collisions is modified