General chemistry 2 Ch12 chemical kinetics

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Final exam part one

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

MUST READS

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

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