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37 Cards in this Set

  • Front
  • Back
energy difference between the reactants and the transition state; the minimum energy the reactants must have for the reaction to occur: Ea
activation energy
the amount of energy required to break a particularbond homolytically, to give radicals: BDE
A:B --> A. + B.

delta H = BDE
bond-dissociation energy
a strongly nucleophilic species (reactive intermediate)with a negatively charged carbon atom having only three bonds; the carbon atom has a nonbonding pair of electrons

-:CH3 nucleophilic strong bases
a highly reactive species (reactive intermediate) with only two bonds to an uncharged carbon atom and with a nonbinding pair of electrons

:CH2 (methylene) both nucleophilic and electrophilic
a strongly electrophilic species (reactive intermediate) with a positively charged carbon atom having only three bonds

+CH3 electrophilic strong acids
carbocation or
carbonium ion or
carbenium ion
substance that increases the rate of a reaction (by lowering the Ea) without being consumed in the reaction
a multistep reaction where a reactive intermediate formed in one step brings about a second step that generates the intermediate needed for the following step
chain reaction
the preliminary step in a chain reaction, where the reactive intermediate is first formed
initiation step
the steps in a chain reaction that are repeated over and over to form the product; the sum of these steps should give the net reaction
propagation steps
any steps where a reactive intermediate is consumed without another one being generated
termination steps
a measure of the heat energy in a system. In a reaction, the heat absorbed or evolved is called the heat of reaction (delta H). A negative delta H is favorable for reaction to occur
reaction consuming heat (increase in enthalpy); having a positive delta H; does not favor reaction
reaction giving off heat (a decrease in enthalpy); a negative delta H; favorable for reaction
measure of diorder or freedom of motion; a positive value, or increase in the delta S is favorable for the reaction to occur.
state of a system such that no more change is taking place; the rate of the forward reaction equals the rate of the reverse reaction
a quantity calculated from the relative concentrations of the products over the concentration of the reactants at equilibrium
equilibrium constant (Keq)
a measure of a reactions tendency to go in the direction written; a decrease or negative delta G is favorable for a reaction to occur
delta G = delta H - T delta S
free energy or
Gibbs free energy
related species on a reaction-energy diagram that are closer in energy are also closer in structure; exothermic reaction, the transition state is closer to the reactants; endothermic reaction, the transition state is closer to the products in energy and in structure
Hammond postulate
breaking of a bond in such a way that one of the atoms retains both of the bonds electrons; forms two ions
A:B --> A:- + B+
heterolytic cleavage or
ionic cleavage
breaking of a bond in such a way that each atom retains one of the bonds two electrons; produce two radicals
A:B --> A. + B.
homolytic cleavage
a donation (or withdrawel) of electron density through sigma bonds
inductive effect
molecule or fragment of a molecule that is formed in a reaction and exists for a finite length of time before it reacts in the next step; it corresponds to relative minimum (a low point) in the reaction-energy diagram
a short lived species that is never present in high concentration because it reacts as quickly as it is formed
reactive intermediate
the study of reaction rates
the step-by-step pathway from reactants to productsshowing which bonds break and which bonds form in what order; includes the structures of all intermediates and arrows to show the movement of electrons
a plot of potential energy changes as the reactants are converted to products; vertical axis is all potential energy and the horizontal is reaction progress
reaction-energy diagram or
potential-energy diagram
highly reactive speciesin which one of the atoms has an odd number of electrons; most commonly a carbon atom with three bonds and an unpaired electron
radical or
free radical
compound added to prevent the propagation of free radical chain reactions; reacts to form a radical that is too stable to propagate the chain
radical inhibitor
the amount of product formed or reactant consumed per unit of time
reaction rate
relationship between the concentrations of the reagents and the observed reaction rate
rate equation or
rate law
the power of a concentration term in the rate equation; overall is the sum of the individual concentration orders
kinetic order
the constant in the rate equation (kr)
rate constant
the slowest step in a multi step sequence of reactions; step with the highest-energy transition state
rate-limiting step or
rate-determining step
stabilization that takes place by delocalizationof electrons in a pi-bonded system; stabilizes cations, radicals, and anions
resonance stabilization
a reaction in which one atom replaces another, usually as a substituent on a carbon atom
study of the energy changes that accompany a chemical transformations; generally concerned with systems at equilibrium
position of the activated complex; the state of highest energy between reactants and products; a relative maximum (high point) on the reaction-energy diagram
transition state