Ch. 5: Chemical Kinetics Flashcards
rate-determining step
the slowest step in a mechanism
the rate of the whole reaction is only as fast as the rate-determining step
collision theory
rate of a reaction is proportional to the number of collisions per second between the reacting molecules
activation energy
“energy barrier”
- minimum energy of a collision necessary for a reaction to take place
- only a fraction of collisions will exhibit this energy
equation for the rate of a reaction according to collision theory
rate = Z * f
total # of collisions per second * fraction of collisions that are effective
transition state theory
when molecules collide with energy equal to or greater than the activation energy they form a theoretical transition state
reaction coordinate
traces a reaction from reactants to products
energy in the transition state
higher than products or reactants
free energy change of the reaction
difference between free energy of products and free energy of reactants
exergonic reaction
negative free energy change, energy is given off
endergonic reaction
positive free energy change, energy is absorbed
activation energy of the forward reaction
difference in free energy between transition state and reactants
activation energy of the reverse reaction
difference in free energy between transition state and products
increase in concentration has what effect on reaction rate
increase concentration –> increase collision rate –> increase reaction rate
increase in temperature has what effect on reaction rate
increase in temperature –> increase in kinetic energy –> increase in reactants reaching activation energy –> increase in rate AT IDEAL TEMPERATURES
units of rate
mol / L*s (mols per liter per second)
OR
M/ s (molarity per second)
rate law
rate = k[A]^x[B]^y
what does k represent in the rate law
reaction rate coefficient or rate constant
what do x and y represent in the rate law
the orders of the reaction
when are the stoichiometric coefficients usual to the orders of the reactants
on the reactant side of the rate determining step
overall reaction order is equal to
x + y
what is the rate law for a zero-order reaction
rate = k[A]0[B]0=k
what is the rate of a zero-order reaction dependent on
rate is
- independent of changes in concentration of reactants
- equal to k
what is the rate of a first-order reaction dependent on
rate is dependent on changes in concentration of only one reactant
what is the rate law of a first-order reaction
rate = k[A]1 OR =k[B]1
what is the rate of a second-order reaction dependent on
rate is dependent on changes
- in concentration of both reactants OR
- on the the square the concentration of one reaction
what is the rate law of a second-order reaction
rate = k[A]1[B]1 OR = k[A]2 OR = k[B]2
why are high order reactions rare
high order reactions require three molecules (rather than one or two) colliding in correct orientation with sufficient energy
what is unique about mixed-order/broken-order reactions
orders are integers or change throughout the reaction
