CHM
2046C Module 9: Chapter 12 Key Terms Part K: Key Terms Chapter 12 - McMurry
Define the
following chapter 15 key terms:
activation energy (Eact) – is the minimum energy that must be
added to the reaction for a reaction to occur; on a reaction coordinate
diagram, it corresponds to the energy required to go from the reactants up to
the highest point in the energy diagram.
Arrhenius equation: An equation that relates the rate
constant, temperature, and energy of activation:
K = A∙e-Ea/RT
Average rate: The rate over a period of time; this
is calculated by taking two points on the concentration vs. time graph and
dividing the change in concentration by the chage in
time.
Bimolecular: a term used to describe the elementary
step involving two molecules 9or ions, atoms, or free radicals).
activated complex
Catalyst: a material that speeds up the reactiuon without being permanently changed in the
reaction.
Chemical Kinetics – the study of the rates of chemical
reactions
Collision theory: a theory of chemical reaction rates
that proposes that reactant molecules must collide with each other in order to
react and that the molecules must collide with proper orientation and with
sufficient energy.
Elementary step: an individual step in a reaction
mechanism.
Enzyme: A biological catalyst
first order reactant
– the rate of the reaction depends on the concentration of this reactant raised
to the first power [A]1 or the rate of the reaction varies directly with a
change in concentration of this reactant..
Half-life (t
˝
): the time required for the
concentration of a reactant to decrease to half its initial value.
Heterogeneous
Catalyst – A catalyst
that is present in a different phase from the reacting substances.
Homogeneous Catalyst – A catalyst that is present in the
same phase as the reacting substances.
Initial rate: the instantaneous reaction rate at
the start of a reaction.
Instantaneous rate:
the rate at a particular time: this is calculated by calculating the
slope of the line tangent to the concentration vs. time graph at this
time.
Integrated rate law: An equation that relates the
concentration and time; this equation is derived from the rate law using
integral calculus.
Intermediate (or
reaction intermediate):
a material that is produced in one step of a mechanism but is consumed in a
later step.
Molecularity:
the number of reactant molecules (or ions, atoms, or free radicals) involved in
an elementary step.
order (of a reactant): the exponent to which a reactant’s concentration is
raised in the rate law.
Rate constant: the proportionality constant in the
rate equation.
Rate Determining Step
(also Rate Limiting Step):
The slowest step in a reaction mechanism and therefore the step that limits the
overall reaction.
Rate Equation (rate
law): the
mathematical relationship between reactant concentrations and the reaction
rate.
Reaction coordinate
diagram: A diagram of
which the y-axis is energy (or enthalpy) and the x-axis is a measure of the
reaction’s progress.
Reaction Mechanism: the sequence of bond-making and
bond-breaking steps that occur during the conversion of reactants to products
during a chemical reaction.
Reaction rate: The change in concentration of a
substance divided by the change in time; if the material is a reactant, we must
change the sign of this calculation.
second order reactant
- the rate of the reaction depends on the concentration of this reactant raised
to the second power [A]2
Termolecular:
a term used to describe an elementary step involving three molecules (or ions,
atoms, or free radicals); These steps are vary rare ( a
three body collision).
Total order: the sum of the exponents in a rate
equation.
Transition state:
the chemical species present at the maximum in energy in a reaction
coordinate diagram: it consists of atoms in some intermediate state of bond
breaking and bond formation.
Unimolecular:
A term used to describe the elementary step involving only one molecule (*or
ion, atom, or free radical).
zero order reactant-the
rate of the reaction does not depend on the concentration of this reactant [A]0