Chapter 14 & 15 Flashcards
activation energy (Ea)
The minimum energy needed for reaction; the height of the energy barrier to formation of products. (Section 14.5)
activated complex (transition state)
The particular arrangement of atoms found at the top of the potential-energy barrier as a reaction proceeds from reactants to products. (Section 14.5)
active site
Specific site on a heterogeneous catalyst or an enzyme where catalysis occurs. (Section 14.7)
adsorption
The binding of molecules to a surface. (Section 14.7)
Arrhenius equation
An equation that relates the rate constant for a reaction to the frequency factor, A, the activation energy, Ea, and the temperature, T:K.
Beer’s law
The light absorbed by a substance (A) equals the product of its extinction coefficient (e), the path length through which the light passes (b), and the molar concentration of the substance (c): A
bimolecular reaction
An elementary reaction that involves two molecules. (Section 14.6)
catalyst
A substance that changes the speed of a chemical reaction without itself undergoing a permanent chemical change in the process. (Section 14.7)
chemical equilibrium
At equilibrium the concentrations of the reactants and products remain constant. (Chapter 15: Introduction)
chemical kinetics
The area of chemistry concerned with the speeds, or rates, at which chemical reactions occur. (Chapter 14: Introduction)
collision model
A model of reaction rates based on the idea that molecules must collide to react; it explains the factors influencing reaction rates in terms of the frequency of collisions, the number of collisions with energies exceeding the activation energy, and the probability that the collisions occur with suitable orientations. (Section 14.5)
elementary reaction
A process in a chemical reaction that occurs in a single event or step. An overall chemical reaction consists of one or more elementary reactions or steps. (Section 14.6)
enzyme
A protein molecule that acts to catalyze specific biochemical reactions. (Section 14.7)
equilibrium constant
The numerical value of the equilibrium-constant expression for a system at equilibrium. The equilibrium constant is most usually denoted by Kp for gas-phase systems or Kc for solution-phase systems. (Section 15.2)
equilibrium-constant expression
The expression that describes the relationship among the concentrations (or partial pressures) of the substances present in a system at equilibrium. The numerator is obtained by multiplying the concentrations of the substances on the product side of the equation, each raised to a power equal to its coefficient in the chemical equation. The denominator similarly contains the concentrations of the substances on the reactant side of the equation. (Section 15.2)
first-order reaction
A reaction in which the reaction rate is proportional to the concentration of a single reactant, raised to the first power. (Section 14.4)
frequency factor (A)
A term in the Arrhenius equation that is related to the frequency of collision and the probability that the collisions are favorably oriented for reaction. (Section 14.5)
Haber process
The catalyst system and conditions of temperature and pressure developed by Fritz Haber and coworkers for the formation of NH3 from H2 and N2. (Section 15.2)
half-life
The time required for the concentration of a reactant substance to decrease to half its initial value. (Section14.4)
heterogeneous catalyst
A catalyst that is in a different phase from that of the reactant substances. (Section 14.7)
heterogeneous equilibrium
The equilibrium established between substances in two or more different phases, for example, between a gas and a solid or between a solid and a liquid. (Section 15.4)
homogeneous catalyst
A catalyst that is in the same phase as the reactant substances. (Section 14.7)
homogeneous equilibrium
The equilibrium established between reactant and product substances that are all in the same phase. (Section 15.4)
instantaneous rate
The reaction rate at a particular time as opposed to the average rate over an interval of time. (Section 14.2)
intermediate
A substance formed in one elementary step of a multistep mechanism and consumed in another; it is neither a reactant nor an ultimate product of the overall reaction. (Section 14.6)
law of mass action
The rules by which the equilibrium constant is expressed in terms of the concentrations of reactants and products, in accordance with the balanced chemical equation for the reaction. (Section 15.2)
Le Châtelier’s principle
A principle stating that when we disturb a system at chemical equilibrium, the relative concentrations of reactants and products shift so as to partially undo the effects of the disturbance. (Section 15.7)
lock-and-key model
A model of enzyme action in which the substrate molecule is pictured as fitting rather specifically into the active site on the enzyme. It is assumed that in being bound to the active site, the substrate is somehow activated for reaction. (Section 14.7)
molecularity
The number of molecules that participate as reactants in an elementary reaction. (Section 14.6)
overall reaction order
The sum of the reaction orders of all the reactants appearing in the rate expression when the rate can be expressed as rate
rate constant
A constant of proportionality between the reaction rate and the concentrations of reactants that appear in the rate law. (Section 14.3)
rate law
An equation that relates the reaction rate to the concentrations of reactants (and sometimes of products also). (Section 14.3)
rate-determining step
The slowest elementary step in a reaction mechanism. (Section 14.6)
reaction mechanism
A detailed picture, or model, of how the reaction occurs; that is, the order in which bonds are broken and formed and the changes in relative positions of the atoms as the reaction proceeds. (Section 14.6)
reaction order
The power to which the concentration of a reactant is raised in a rate law. (Section 14.3)
reaction quotient (Q)
The value that is obtained when concentrations of reactants and products are inserted into the equilibrium expression. If the concentrations are equilibrium concentrations, Q
reaction rate
A measure of the decrease in concentration of a reactant or the increase in concentration of a product with time. (Section 14.2)
second-order reaction
A reaction in which the overall reaction order (the sum of the concentration-term exponents) in the rate law is 2. (Section 14.4)
substrate
A substance that undergoes a reaction at the active site in an enzyme. (Section 14.7)
termolecular reaction
An elementary reaction that involves three molecules. Termolecular reactions are rare. (Section 14.6)
transition state (activated complex)
The particular arrangement of reactant and product molecules at the point of maximum energy in the rate-determining step of a reaction. (Section 14.5)
unimolecular reaction
An elementary reaction that involves a single molecule. (Section 14.6)
What are factors that affect reaction rates?
- Physical state of the reactants
- Reactants concentrations
- Temperature
- Presence of a catalyst
What does it mean if k is 0?
There is no reaction
