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
intermediate
a substance that is neither a reactant nor a product in the overall reaction (formed in 1 elementary reaction and consumed in the next); multistep mechanisms involve 1 or more of these
Rate-determining step
overall rate of a reaction cannot exceed the rate of the slowest elementary step of its mechanism; b/c the slow step limits the overall reaction rate, it is the _____ ______ _____.
Catalyst
substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself in the process
Homogeneous catalyst
a catalyst that is present in the same phase as the reacting molecules
Heterogeneous catalyst
exists in a different phase from the reactant molecules, usually as a solid in contact with either gaseous reactants or with reactants in a liquid solution
adsorption
initial step of heterogeneous catalysis; refers to the binding of molecules to a surface
absorption
uptake of molecules into the interior of another substance
enzymes
efficient biological catalysts; necessary for many reactions in the body to occur at suitable rates
Active site
reaction is catalyzed at a very specific location in an enzyme
substrates
substances that undergo reaction at this site
lock-and-key model
simple explanation for the specificity of an enzyme
nitrogen fixation
process of converting N2 into compounds that plants can use
enzyme inhibitors
substances that bind strongly to the active site and block the entry of the substrate
