Chemistry - Ch 14 Flashcards
Chemical kinetics
the area of chemistry that is concerned with the speeds, or rates, of reactions
Reaction rate
the speed of a chemical reaction; change in the concentration of reactants or products per unit of time; units usually molarity per second (M/s)
Instantaneous rate
the rate at a particular moment in the reaction
Beer’s Law
relates the amount of light being absorbed to the concentration of the substance absorbing the light
Rate law
an equation which shows how the rate depends on the concentration of reactants; generally has the form Rate = k[A]^m[B]^n
Rate constant
the constant k in the rate law; magnitude of k changes with temperature and therefore determines how temperature affects rate
Reaction orders
exponents m & n in a rate law
Overall reaction order
sum of the orders with respect to each reactant in the rate law
First order reaction
one whose rate depends on the concentration of a single reactant raised to the 1st power
Differential rate law
the form of a rate law, which expresses how rate depends on concentration
Integrated rate law
ln[A] subscript t - ln[A] subscript 0 = -kt OR ln ([A] subscript t/[A] subscript 0) = -kt
Second order reaction
one whose rate depends on the reactant concentration raised to the 2nd power or on the concentrations of 2 different reactants, each raised to the 1st power; rate = k[A]^2
Half-life
time required for the concentration of a reactant to reach one-half of its initial value
Collision model
based on the kinetic-molecular theory, accounts for concentration of reactants and temperature at the molecular level; central idea: molecules must collide to react
Activation energy
the minimum energy required to initiate a chemical reaction (E subscript a)
Activated complex (transition state)
particular arrangement of atoms at the top of the barrier (barrier = energy necessary to force the molecule through the relatively unstable intermediate state to the final product)
Arrhenius equation
most reaction-rate data obeyed an equation based on 3 factors: (1) fraction of molecules possessing an energy of E subscript a or greater (2) the # of collisions per second, & (3) the fraction of collisions that have the appropriate orientation; k=Ae^(-E subscript a/RT)
Frequency factor
A from Arrhenius equation; related to the frequency of collisions and the probability that the collisions are favorably oriented for reaction
Reaction mechanism
process by which a reaction occurs
Elementary reactions (elementary processes)
single collision (event, step)
Molecularity
number of molecules that participate as reactants in an elementary reaction
unimolecular
a single molecule is involved in a reaction
bimolecular
elementary reactions involving the collision of 2 reactant molecules
termolecular
elementary reactions involving the simultaneous collision of 3 molecules
