Book: Key Terms: 16 Flashcards
activation energy (E_a)
an energy threshold that the colliding molecules must exceed in order to react
active site
a small part of an enzyme’s surface, a region whose shape results from the amino-acid side chains involved in catalyzing the reaction
Arrhenius equation
k = A e^(-E_a / (RT)), where k is the rate constant, T is the absolute temperature, R is the universal gas constant, E_a is the activation energy
average rate
over a given period of time, the average rate is the slope of the line joining two points along the curve
bimolecular reaction
a reaction in which two particles collide and react
catalyst
a substance that increases the reaction rate without being consumed
chemical kinetics
the study of how fast reactants change into products throughout the course of a chemical reaction
collision theory
atoms, molecules, ions, must collide to react in this model
effective collision
the collisions that actually lead to product because the atoms that become bonded in the product make contact
elementary reaction (elementary setup)
the individual steps that make up a reaction mechanism. Each describes a single molecular event—one particle decomposing, two particles combining, etc.
enzyme
a protein catalyst
enzyme-substrate complex
substrate and enzyme form an intermediate enzyme-substrate complex (ES), whose concentration determines the rate of formation of product.
frequency factor
the term A in the Arrhenius equation, which gives molecular orientation: it is given by A = pZ, where p is the orientation probability factor and Z is the collision frequency.
half-life (t_1/2)
the time it takes for reactant concentration to reach half its initial value in a reaction.
heterogeneous catalyst
speeds up a reaction in a different phase, such as solids interacting with gas or liquid reactants.
homogeneous catalyst
catalyst that is both in the same phase as the reactants and products and exists in a solution with the reaction mixture.
hydrogenation
An example of a heterogeneous catalyst which reduces carbon-carbon double bonds to single bonds by the introduction of H2
induced-fit model
In this model, the substrate in enzyme action induces the active site to adopt a perfect fit; the enzyme changes shape when the substrate lands at the active site.
initial rate
The instantaneous rate at the moment the reactants are mixed (t=0).
instantaneous rate
The rate at a particular instant during the reaction.
integrated rate laws
Forms of the rate equation that include time as a variable as to answer questions about how long it takes a specific process to occur.
lock-and-key model
An older model which suggests enzyme action is characterized by a “key” (substrate) fitting a “lock” (active site), and then the chemical change proceeds.
molecularity
Characterizes an elementary step; equal to the number of reactant particles in the step.
rate constant
A proportionality constant showing up in the rate law that is specific for a given reaction at a given temperature.
rate-determining (rate-limiting) step
One step in a set of elementary steps is usually much slower than all of the others. This is the rate-determining step (or rate-limiting step), as it limits how fast the overall reaction proceeds.
rate law (rate law)
Expresses the rate of reaction as a function of concentrations and temperatures: Rate = k [A]^m [B]^n …
reaction energy diagram
Plots how potential energy changes as the reaction proceeds from reactants to products (the reaction progress).
reaction intermediate
A substance formed in one step of the mechanism of a reaction and used up in a subsequent step during the reaction.
reaction mechanism
A sequence of single reaction steps that sum to the overall equation for a reaction.
reaction orders
The exponents m and n in the rate law: r = k [A]^m [B]^n, which generally define how the rate is affected by reactant concentration.
reaction rate
The change in the concentrations of reactants or products as a function of time.
substrate
Reactant molecules in biological reactions involving active sites.
transition state (activated complex)
In the transition state theory, at some point during a reaction an unstable species neither reactant nor product arises with partial bonds at the instant of highest potential energy. The activation energy of a reaction is used to reach the transition state.
transition state theory
A model that focuses on the high-energy species that exists at the moment of an effective collision when reactants are becoming products.
unimolecular reaction
An elementary step that involves the decomposition or rearrangement of a single particle.
