Term | Definition |
chemical kinetics | study of rates of rxns, the effect of rxn conditions on these rates, and the mechanisms implied by such observations |
mechanism | series of steps thru which a chemical rxn occurs |
Rate-determining Step | the slowest step in a mechanism; overall rxn can't go faster than this step |
Molarity | M; mol/L |
Rate | M/s or mol/Lxs |
Rate Law | the rate is proportional to the product of the concentrations of the reactants raised to some power; rate = k [A]^x [B]^y |
Rate Constant | k |
Orders of rxn | exponents on the reactants (x and y) |
overall order of a rxn | sum of exponents (x + y) |
Zero-Order rxn | constant rate independent of reactant concentration so rate law is rate = k |
First-Order rxn | rate is proportional to the concentration of one reactant; rate = k [A] (radioactive decay) |
Second-Order rxn | rate is proportional to the concentration of two reactants or the square product of a single reactant; rate = k[A]2 or k[A][B] |
Mixed-Order | has a fractional order; rate = k[A]^1/3 |
Higher-Order rxn | order greater than 2 |
Collision Theory of Chemical Kinetics | the rate of a rxn is proportional to the number of collisions per second btwn molecules |
Activation E | min amount of E necessary for a rxn to take place; rate = fZ |
rate = fZ | Z = number of collisions/s
f = fraction of effective collisons |
Transition State/Activated Complex | greatest E, once formed it can dissociate into products or revert to reactants; exists at top of E barrier |
Enthalpy | H; difference btwn PE of products and reactants. Products-Reactant |
Exothermic | negative enthalpy and heat was given off |
Endothermic | positive enthalpy and heat is absorbed/added |
Reactant Concentrations affecting Rate | the higher the concentrations, the faster the rate cuz more collisions cept zero order rxns |
Temperature | higher the temp, faster the rate |
Medium | some reactions go faster in aqueous soln and others more in benzene; state (s l or g) can have effect too |
Catalysts | substances that increase rxn rate w/o being consumed; they lower Ea.; increases frequency of collisions |
Equilibrium | when there is no NET change in the concentrations of the products and reactants during a reversible rxn |
Kc | equilibrium constant; kf/kr |
Law of Mass Action | Kc = prducts^exponents/reactants^exponents |
Keq characteristics | 1. pure solids and liquids DONT appear in equilibrium constant
2. at a given temp
3. If Keq is more than 1, then the mixture will have more products
4. If Keq is less than 1, then more reactants |
Le Chatelier's Principle | a system to which a stress is applied tends to change so as to relieve the applied stress; used to determine the direction of a rxn after a stress is applied to equilibrium |
Changes in Pressure/Volume | only for gases; V and P inversely proportional; If P increases, shift to least moles; if V increases, P decreases and shift to more moles |
Temperature Changes | alters position of equilibrium and alters the value of equilibrium constant |