Kinetics Flashcards
Chemical kinetics
The study of chemical reactions and the factors which affect them
Rate
Is the change in conc per unit time
Do the units for rate ever change and what are they?
No they do not change
mol L-1 s-1
Rate law
Is the relationship between rate and concentration
rate α [concn]2
Rate Law - 0 order
Rate independent of concentration
rate = constant
Rate Law - 1 Order
Rate is proportional to the concentration of the reactant
Activation energy
Ea is the energy required by the reactants to reach the transition state.
Ea in rate constant = Ae − Ea/RT
Reactive intermediate
A substance that is produced in one step of a reaction mechanism and consumed in a subsequent step.
e.g. A + B → C; C + D → products [C is a reactive intermediate.]
Catalyst
Substance that affects rate of reaction, but is unchanged at the end of the reaction.
e.g. enzymes, I − in decomposition of H2O2etc
Rate constant
Proportionality constant (k) in rate equation.
e.g. 1st order, rate = k[concentration]
Half life
time taken for concentration to fall to half its initial value.
e.g. For a 1st order reaction t½ = ln2/k
Integrated rate law
relationship between concentration and time.
e.g. [A] = [A]0e-kt
Homogeneous catalyst
catalyst in same phase of the reactants that affects the rate of reaction but is unchanged at the end of the reaction
(e.g. I -/H2O2).
Heterogeneous catalyst
Substance, in a different phase from the reactants, that affects the rate of reaction but is unchanged at the end of the reaction.
e.g. many metals such as catalytic converters
Elementary reaction
An elementary reaction is a single bond breaking and/or bond forming step passing through a single transition state
S config for enantiomers
descending priority of three higher ranked anti-clockwise
Which is the most stable carbocation? rank them in order
stability 3 ° >2 ° >1 ° .
Which type of molecule would have highest bp?
A linear one
No branching, “strongest” intermolecular interactions.
Strongest intermolecular interactions (STATE WHAT THE BONDING IS)
Why would a compound have lowest bp?
least polar; no possibility of intermolecular hydrogen bonding.
Rate Law = Second Order
where rate α [concn]2
where the overall order in the rate law is two.
e.g. rate α [A][B] (1st order in each of A and B)
In chromatography, which polar or nonpolar moves in alumina column?
Least polar - therefore least attraction to the polar stationary phase so moves most quickly with
the mobile phase
What is a vinyl halide?
Halogen attached to sp2 carbon
R enantiomer?
descending order of priority of three higher ranked substituents in a clockwise direction.
Transition state
in an elementary reaction is the point of highest energy between reactants and products
Arrhenius equation
Equation that describes how rate constants depend on temperature and activation energy.
Rate determining step
The slowest step in a reaction mechanism is the rate determining step
Aryl group
Halogen directly bonded to sp2 carbon of aromatic ring
Diastereomers?
Configurational stereoisomers with a non mirror image relationship
Constitutional isomers?
Same molecular formula, different atom to atom bonding sequence.
Third order reaction
Where the overall reaction order in the rate law is 3
The rate is 3rd order in a single reactant or 2nd order in one and 1st order in another or 1st order in each of three reactants.
rate α [A]3 or
rate α [A]2[B] or rate α [A][B][C]
Average rate
is the change in rate over a time interval.
change concentration/change t (SQUARE LOOKING THING ON CURVED GRAPH)
Instantaneous rate
instantaneous rate is the rate at a specific point in time during the course of the reaction
Tangent gives instantaneous rate
Reaction mechanism
is the collection of individual (elementary) steps required to go from reactant to product.
Units of 0 order
mol L-1 s-1
Units 1st order
s-1
Units for 2nd order
L mol-1 s-1
Units for 3rd order
L2 mol-2 s-1
