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OAT - Chem
Chapter - 5 Chemical Kinetics/Equilibrium
| 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 |
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