Zusammenfassung der Ressource
Chemical Kinetics
- Vocabulary
- 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