TOPIC 8- CHEMICAL KINETICS Flashcards
the area of chemistry concerned with the
speeds, or rates, at which a chemical reaction occurs.
Chemical Kinetics
refers to the rate of a reaction, or the reaction rate which is the change in the concentration of a product or reactant with time.
Kinetics
What are the factors affecting reaction rate?
- Concentration
- Physical State
- Temperature
- Catalysts
Most chemical reactions proceed faster if the concentration
of one or more of the reactants is
increased
The more ready molecules collide with each other,
the more rapid they react
Raising the temperature increases the
number and the energy of collisions
Molecules must collide with enough energy to
react
are agents that increase reaction rates without being
used up.
catalysts
Catalysts catalyze chemical reaction rates by lowering the
activation energy
is the energy needed for the chemical
reaction to begin.
activation energy
is a change in some variable per unit time.
Rate
is the change in concentrations of reactants or
product in a chemical reaction per unit time.
Reaction Rate
Reactant concentration decrease as
solution concentration increase
is the reaction rate between any two intervals.
Average Rate
is the reaction rate at a specific point in
time.
Instantaneous rate
is the instantaneous rate at the moment the
reactants are mixed.
Initial rate
expresses the rate as a function of reactant
concentrations and temperature.
rate law
are used to measure the concentration
of a reactant or product that absorbs (or emits) light of a narrow
range of wavelengths.
spectrometric methods
are used to measure the rate when
nonionic reactants for ionic products, or vice versa since the
conductivity of the solution changes over time.
Conductometric methods
are used if the reaction involves a
change in the number of moles of gas.
Manometric methods
In manometric methods, The rate can be determined from the change in ___________
(at constant volume and temperature) over time.
pressure
are used to measure the rates of
slow reactions, or of those that can be easily slowed.
Direct Chemical Methods
A small, measured portion called _______ of the reaction
mixture is removed, and the reaction in this portion is
stopped by rapid cooling.
aliquot
We can
determine the reaction order and then the rate constant of the
reaction from
reactant concentration
Note that the
exponents of L and mol in the unit of the rate constant is equal to the
overall reaction order minus one
enable us to calculate the rate of a reaction
from the rate constant and reactant concentrations
Rate law expressions
The rate laws can also be used to determine the concentrations
of reactants at anytime during a reaction by employing different
forms,
integrated rate laws
These are reactions whose rate depends on the reactant concentration
raised to the first power.
First Order Rate Laws
are reactions whose rate depends on the concentration of one
reactant raised to the second power or on the concentrations of two
different reactants, each raised to the first power.
Second Order Rate Laws
These are reactions whose rate is a constant, independent of reactant
concentration.
Zeroth Order Rate Laws
time required for the reactant
concentration to reach half its initial value.
Half-life of a reaction
is a constant, independent of
reactant concentration.
Half-life of a First-Order Reaction
does depend on reactant
concentration and the half-life is inversely proportional to the initial
concentration.
Half-life of a second-order reaction
is directly proportional to the initial reactant concentration.
Half-Life of a Zero-Order Reaction
Most chemical reactions occur by a series of steps called the
reaction mechanism
a species that is canceled from
both sides of the reaction (not a reactant or product.)
intermediate
Each of these two reactions is called an
elementary Step
The sequence of elementary steps that leads to product formation is the
reaction mechanism
is always formed in an early elementary step and consumed in a later elementary step.
intermediate
is the number of molecules reacting in an elementary step.
Molecularity of a reaction
elementary step with 1 molecule
Unimolecular reaction
elementary step with 2 molecule
Bimolecular reaction
elementary step with 3 molecule
Termolecular reaction
The rate law of a reaction mechanism is derived from the
slowest step called
rate-determining step
A reaction mechanism must satisfy the following:
- The sum of the elementary steps must give the overall balanced
equation for the reaction. - The mechanism must agree with the experimentally determined
rate law.
is built around the central idea that
molecules must collide to react.
Collision model
proposed the existence of the activation
energy that must be overcome to produce a chemical reaction.
Svante Arhenius
The higher the activation energy, the ___________________ at a
given temperature.
slower the reaction
Many collisions, even though they have the required energy, still
do not produce a reaction due to
molecular orientation during collisions
Two requirements must be satisfied for reactants to collide:
- The collision must involve enough energy to produce the
reaction; that is, the collision energy must equal or exceed the
activation energy. - The relative orientation of the reactants must allow formation of
any new bonds necessary to produce products.
what are the types of catalysts?
- Homogeneous catalyst
- Heterogeneous catalyst
is one that is present in the same
phase as the reacting molecules.
Homogeneous Catalyst
exists in a different phase, usually as
a solid.
Heterogeneous Catalyst
refers to the collection of one substance on the
surface of another substance
Adsorption
refers to the
penetration of one substance into another.
Absorption
