Reaction rate- is the speed at which a chemical reaction occurs
Chemical Kinetics- is the area of chemistry concerned with the speeds, or rates, of reactions.
instantaneous rate- of a reaction, which is the rate at a particular instant during the reaction.
catalyst- is a substance that increases the rate of a reaction without undergoing a net chemical change itself
homogeneous catalyst- is one that is in the same phase as the reactants.
heterogeneous catalyst -has a different phase from the reactants
reaction mechanism -details the individual steps that occur in the course of a reaction.
unimolecular, bimolecular, or termolecular,- depending on whether
one, two, or three reactant molecules are involved
Factors that affect reaction rates
1- Physical state of the reactants. Reactants must come together to react. The more readily reactant molecules
collide with one another, the more rapidly they react
2- Reactant concentrations. Most chemical reactions proceed faster if the concentration of one or more
reactants is increased.
3- . Reaction temperature. Reaction rates generally increase as temperature is
increased.
4- The presence of a catalyst. Catalysts are agents that increase reaction rates without themselves being
used up.
Reaction rates
The speed of an event is defined as the change that occurs in a given time interval, which means that
whenever we talk about speed, we necessarily bring in the notion of time.
Similarly, the speed of a chemical reaction—its reaction rate—is the change in the concentration of
reactants or products per unit of time.
Reaction Orders
The Exponents in the Rate Law The rate law for most reactions has the form
Rate = k[reactant 1]m[reactant 2]n The exponents m and n are called
reaction orders.
THE CHANGE OF CONCENTRATION
WITH TIME
first order reactions
n is one whose rate depends on the concentration of a single
reactant raised to the first power
integrated rate law
ln[A]t - ln[A]0 = -kt or
ln [A]t [A]0 = -kt
differential rate law
Rate = - [A]/t = k[A]
second order reactions
rate depends either on a reactant concentration raised to the second
power or on the concentrations of two reactants each raised to the
first power.
half life
Half-life is a convenient way to describe how
fast a reaction occurs, especially if it is a
first-order process. A fast reaction has a short
half-life