kinetics

Kinetics

Kinetics|P. E. Diagrams|Factors Effect Rate|Spontaneous|Top

Kinetics

A. Kinetics: The study of the speed of the reaction (Reaction Rate) and the way the reaction happens (Reaction Mechanism).

B. Why do reactions occur?
	1. Frequent Collisions
	2. Effective Collisions
		a) Proper energy b) Proper angle

Kinetics|P. E. Diagrams|Factors Effect Rate|Spontaneous|Top

II.

Potential Energy Diagrams:
used to illustrate the progress of a chemical reaction

Exothermic | Endothermic | Definitions
Exothermic (Energy is produced)
Reactants -->Products + Heat Energy

A: Activation Energy
B: Potential Energy of the Reactants
C: H
D: Activated Complex
E: Activation Energy of Reverse Reaction
F: Potential Energy of the Products

Exothermic | Endothermic | Definitions

Endothermic (Energy is used)
Reactants + Heat Energy --> Products

Endothermic PE Diagram

A: Activation Energy
B: Potential Energy of the Reactants
C: H
D: Activated Complex
E: Activation Energy of Reverse Reaction
F: Potential Energy of the Products

Exothermic | Endothermic | Definitions
A. Activation Energy:
Energy required to start a reaction (to get up the hill).

B: Potential Energy of the Reactants:
Energy contained in the reactants at the start of the reaction.

C. Heat of Reaction (H):
Energy absorbed or released during a reaction.
H = ENTHALPY

H = Hproducts - Hreactants
-

H = Exothermic
+

H = Endothermic
REFERENCE TABLE I *bottom

D: Activated Complex
The peak of the curve. The maximum energy in the reaction.

E: Activation Energy of Reverse Reaction
Energy required to start the reverse reaction.

F: Potential Energy of the Products
Energy contained in the products at the end of the reaction.

Factors that effect the
Rate of Reaction

Concentration | Catalyst | Temperature | Nature | Surface Area

Concentration of Reactants
If you increase concentration of
particles, indicated with [brackets],
you get more collision of particles and
therefore you increase reaction rate.

Concentration | Catalyst | Temperature | Nature | Surface Area

Catalyst
A catalyst lowers the activation energy of both the forward and
reverse reactions equally. We therefore shorten the reaction
pathway and the reaction will speed up.

catalyst

Concentration | Catalyst | Temperature | Nature | Surface Area

Temperature
If you increase temperature then you increase the average kinetic energy of the particles. This insures that the particles have the proper energy for effective collisions. This will increase the rate of reaction.

Concentration | Catalyst | Temperature | Nature | Surface Area

Nature of the Reactant
Ionic solids reacts better than covalent molecules.
A Solution (aq) reacts faster than a solid. So the
fastest possible reaction will take place when we dissolve
any ionic salt in water to make a solution.

ionic solution
***NaCl (aq)***

Concentration | Catalyst | Temperature | Nature | Surface Area

One large piece
has less surface area for reactions to take place.

Surface Area
If you increase the surface area
you increase the number of collisions
and therefore increase the rate.

As you break the sample into more pieces surface area is increased.

Spontaneous Reactions
A reaction is considered spontaneous if it can occur under a given set of conditions without being forced by the addition of energy.

A. 2 Factors control Spontaneity

1) Enthalpy (

H):
(A gain or loss of heat energy)
a release of energy (-

H) tends to be spontaneous

2) Entropy (S):
(an increase in randomness)
an increase in randomness (+S) tends to be spontaneous
There is an increase in entropy when:
a) There are more products than reactants
KClO3 KCl + O2

and/or

b) Phase change occurs
Solid Liquid or Liquid Gas
(gas has most disorder)

B. Gibbs Free Energy
We measure the spontaneity through the
Gibbs Free Energy Equation
G = H - TS
where H is enthalpy, T is temperature and S is entropy
+

G = not spontaneous reaction
-

G = spontaneous reaction
When enthalpy and entropy don't agree in terms of spontaneity temperature is the deciding factor. A high temperature will favor the entropy term and a low temperature will favor the enthalpy term.