Kinetics Flashcards
Rate of conversion (J)
J = -(1/a)(dnA/dt) = -(1/b)/(dnb/dt)
A & B = -, C & D = +
Reaction rate (r)
r = J/V = -(1/aV)(dnA/dt)
Order of the reaction
The power to which the concentration of a reactant is raised
Rate Law
r = d[P]/dt = k[A]^a[B]^b,
Expressed as a function of the reactant concentrations, set in square brackets, at constant temp
Rate constant
k
Partial orders
a & b
Total order (n)
Sum of the partial orders
First order reactions
aA -> products
r = k[A] = -(1/a)(d[A]/dt)
[A] = [A]o•e^(-ka•t)
ln([A]/[A]o) = -ka•t
First order half life
t(1/2) = ln2/ka
Second order reactions
2 types:
aA -> products
aA + bB -> products
Second order reactions: type 1
d[A]/dt = -ka[A]^2
ka = a • k
Second order half life:type 1
t(1/2) = 1/([A]o•ka)
Second order reaction type: 2
r = k[A][B]
{1/(a[B]o-b[A]o}ln{([B]/[B]o)/([A]/[A]o)} = kt
Nth order reaction
([A]/[A]o)^n-1 = 1+[A]^n-1•(n-1)•ka•t
t(1/2) = (2^n-1 - 1)/(n-1)•[A]o^n-1•ka
Zeroth order reaction
r = d[A]/dt = -ka
[A] = -Ka•t + [A]o
t(1/2) = [A]o/2ka
Reaction mechanism
The process by which the reaction occurs
Reaction intermediates
Species that are formed in one step and consumed in another
Stoichiometric number
The number of occurrences of a step
Elementary reaction
Each step
Initial rate method
Most common way for determining rate laws
Collision theory
Reactants must collide to react. If temperature increases, so does the speed of the molecules and the frequency of collisions
Activation energy
Energy that must be overcome for the reaction to occur
Activated complex
A transition state where kinetic energy is stored as potential energy
Arrhenius’s Equation
k = Ae^(-Ea/RT)
Stark-Einstein Law
During a photochemical reaction, a photon may promote an electron to an excited electronic state where it is more likely to undergo s chemical reaction than in the ground state
Vibrational relaxation
A* is usually produced in an excited vibrational state. Intermolecular collisions transfer part of this vibrational energy to other molecules, and A* relaxes to the lowest excited vibrational state
Internal conversion
A molecule in its lowest vibrational state can make a radiation less transition to a different excited electronic state. For this process to occur A* and A’ must have the same energy. The molecule A’ is generally in a lower electronic state, but higher vibrational state than A*
Internal conversion
The radiationless process where A’ and A are both singlet or triplet states
Interstates crossing
A radiationless process where A* is a singlet electronic state and A*’ is a triplet electronic state
Radiationless deactivation
Occurs when A* transfers its electronic excited energy to another molecule and returns to its ground state: A* + B -> A + B*
Fluorescence
Occurs when light is emitted from an excited electronic state to a lower electronic state without spin change: dS = 0.
Fluorescence
A* for can lose its electronic energy by spontaneously emitting a photon, which brings it to the ground state: A* -> A + hv
Phosphorescence
Process is the emission of radiation from a triplet excited electronic state to a lower singlet state. Entropy > 0.
Quantum yield
of moles reacting per unit time/ # of miles of light absorbed per unit time
