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27 terms

# General chemistry 2 Ch12 chemical kinetics

Final exam part one
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Chemical Kinetics:
The area of chemistry concerned with reaction rates and the sequence of steps by which reactions occur
Reaction Rate
Either the increase in the concentration of a product per unit time or the decrease in the concentration of a reactant per unit time

Concentration change
Rate = _______________________
Time change
Rate Law
An equation that shows the dependence of the reaction rate on the concentration of each reactant
Experimental Determination of a Rate Law
characteristics of First and second order reactions
Type A-->Products
zeroth-order reaction
the rate is independent of the concentration of the reactant.
Elementary Reaction vs overall reation
-A single step in a reaction mechanism, describes an individual molecular event.
-describes the reaction stoichiometry and is a summation of the elementary reactions.
reactive intermediate
formed in one step and consumed in a subsequent step.
Reactions
names from definations above
Molecularity
A classification of an elementary reaction based on the number of molecules (or atoms) on the reactant side of the chemical equation.
Types of molecularities
uni, bi, tetra
reaction rate laws and molecularity
The rate law for an elementary reaction follows directly from its molecularity because an elementary reaction is an individual molecular event
Rate-Determining Step
The slowest step in a reaction mechanism. It acts as a bottleneck and limits the rate at which reactants can be converted to products
Rate Laws for Overall Reactions: Initial Slow Step
slow then fast
Rate Laws for Overall Reactions:Initial Fast Step
fast then slow then fast
Procedure for Studying Reaction Mechanisms
k vs temprature
The rate constant is dependent on temperature
Transition State
The configuration of atoms at the maximum in the potential energy profile. This is also called the activated complex.
Collision Theory
As the average kinetic energy increases, the average molecular speed increases, and thus the collision rate increases.
Collision theory contd
calculating rate
Activation Energy (Ea)
The minimum energy needed for reaction. As the temperature increases, the fraction of collisions with sufficient energy to react increases.
Arrhenius equation
a different form of collision theory equation, where A(=pZ) is the frequency factor
rate constant vs Ea vs T
k decreases as Ea increases
k increases as T increases (as before)
Catalysis
A substance that increases the rate of a reaction without itself being consumed in the reaction. A catalyst is used in one step and regenerated in a later step.

Since the catalyst is involved in the rate-determining step, it often appears in the rate law.
catalyzed vs uncatalyzed
Ea lower vs higher
Homogeneous vs Heterogeneous Catalysts
A catalyst that exists in the same phase as the reactants.(iodide in decomposition of peroxide)
vs
A catalyst that exists in a different phase from that of the reactants.(commercial use eg. gas exhausted from automobile engines)
More on heterogeneous
table on Heterogeneous catalysts