chemical kinetics
area of chemistry that is concerned with speeds, or rates, of reactions
factors that affect reaction rates
physical state of reactants, concentration of reactants, temperature, presence of catalyst
catalyst
agent that increases reaction rates without being used up
speed
the change that occurs in a given interval of time
reaction rate
the speed of a chemical reaction; the change in the concentration of reactants of products per unit of time; can be expressed as either appearance of A or disappearance of B
Average rate of appearance
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Average rate of disappearance
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instantaneous rate
rate at a particular moment of a reaction; determined from the slope of the curve of a graph at a particular point
initial rate
instantaneous rate when t = 0
rate law
an equation that shows how the rate depends on the concentration of reactants
rate constant
the constant k in the rate law that changes with temperature and therefore determines how temperature affects rate
reaction orders
The power to which the concentration of a reactant is raised in a rate law; determined experimentally or using the coefficients of reactants within a balanced equation
overall reaction order
sum of the exponents in a rate law
0th order
Does not affect rate in any way; [A]; slope on graph is straight line. Disappearance of A is independent of [A]
first order reaction
reaction whose rate depends on the concentration of a single reactant raised to the first power; uses the mathematical concept ln[A]
differential rate law
In this rate law, reaction rate depends on the concentration of the reactants not their volumes
integrated rate law
an expression that shows the concentration of a reactant as a function of time.
second order reaction
reaction whose rate depends on the reactant concentration raised to the second power or on the concentrations of two different reactions, each raised to the first power; uses mathematical concept 1/[A]
half life
the time required for the concentration of a reactant to reach one-half of its initial value
collision model
model based on the kinetic-molecular theory that accounts for both the effects of concentration of reactants and temperature on rates at the molecular level
activation energy
the minimum energy required to initiate a chemical reaction
activated complex (transition state)
the particular arrangement of atoms at the top of the barrier, or the energy necessary to force through the relatively unstable intermediate state of the final product
Arrhenius equation
equation that incorporates the fraction of molecules possessing an energy of Ea or greater, the number of collisions per second, and the fraction of collisions that have the appropriate orientation
frequency factor
the constant A in the Arrhenius equation that does not change as temperature is varied and is related to the frequency of collision and the probability that the collisions are favorably oriented for the reaction
reaction mechanism
describes the process by which a reaction occurs
elementary reaction
chemical process that occurs in a single step;
a reaction in which reactants are converted to products in a single step
molecularity
characteristic determined by the number of molecules that participate as reactants in an elementary reaction
unimolecular
elementary reaction in which a single molecule is involved
bimolecular
elementary reaction involving the collision of two reactant molecules
termolecular
elementary reaction involving the simultaneous collision of three molecules; not probable
multistep mechanism
net change represented by a balanced equation that consists of a sequence of elementary steps
intermediate
a substance that is neither a reactant nor product within the final net equation because it is formed in one elementary step and consumed in the next, having no overall effect on the multistep mechanism
rate-determining step (slow)
since the overall rate for a reaction can not exceed the rate of the slowest elementary step in its mechanism, this slow step limits the overall reaction
catalyst
a substance that changes the speed of a 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
a catalyst that exists in a different phase from the reactant molecules
adsorption
the binding of molecules to a surface; usually the initial step in heterogeneous catalysis
Units of rate constant
Unit of rate = (units of rate constant) (units of concentration) ^2
absorption
taking of molecules into the interior of a substance
Enzymes
Large protein molecules that catalyze a specific reaction
Active site
The specific location in the enzyme where catalysis occurs
Lock and Key
The substrate must fit the enzyme exactly in order for catalysis to take place
Enzyme- substrate complex
Combo of enzyme & substrate
Enzyme inhibitors
When a molecule other than the specific substrate binds to the active site and prevents the entry of the substrate.
Turnover Number
Number of indiviudual catalyzed reactions that occur at a particular active site.
Beer's Law
The relationship of absorbed light to the concentration of the substance absotbing the light is governed by...