Chemical Kinetics Flashcards
Mechanism
The series of steps through which a chemical reaction occurs
Rate-determining step
The slowest step in a mechanism
Chemical kinetics
The study of the rates of reactions
Reaction rate
The change of concentration of reactant or product with respect to time
mol/Ls
Rate law
Rate is proportional to the product of the concentrations of the reactants raised to some power multiplied by the rate constant K
Rate constant
A constant of proportionality between the chemical reaction rate and concentration of the reactants
Reaction order
The sum of the exponents in the rate law
Zero-order reaction
Constant rate independent of the reactants' concentration rate = k M/s [A] = [A0] - kt half-life = 1/2 [A0]/k
First-order reaction
Rate proportional to the concentration of one reactant rate = k[A] s-1 [At] = [A0]e^-kt half-life = ln2/k
Second-order reaction
Rate proportional to the product of the concentration of 2 reactants or the square of the concentration of 1 reactant
rate = [A][B]
M-1s-1
Higher-order reaction
An order greater than 2
Mixed-order reaction
Fractional order
Collision theory
The rate of a reaction is proportional to the number of collisions per second between reacting molecules
Effective collision
Occurs if molecules collide with the correct orientation and sufficient force to break existing bonds and form new ones
Activation energy
The minimum energy of collision necessary for a reaction to take place
Transition state theory
When molecules collide with sufficient energy, they form a transition state in which old bonds are weakened and new bonds begin to form
Potential energy diagram
Illustrates the relationship between the activation energy, heats of reactions, and the potential energy of the system before and after the reaction
Enthalpy
The difference between the potential energy of the products and reactants
Exothermic reaction
Heat given off
Negative enthalpy change
Endothermic reaction
Heat absorbed
Positive enthalpy change
Catalyst
A substance that increases reaction rate without being consumed
Lowers activation energy
Increases frequency of collisions, change orientation to increase effective collisions, donate electron density, reduce intramolecular bonding
