Chemical Kinetics Flashcards
Gibb’s free energy
Determines spontaneity
Mechanism
Steps of the reaction
Rate of the whole reaction is only as fast as
The rate-determining step
Collision theory of chemical kinetics
The rate of reaction is proportional to the number of collisions per second between reacting molecules with correct orientation and with enough energy to break existing bonds and form new ones
Activation energy/Ea
minimum energy of collision necessary for a reaction to take place
Rate=
Z x f
Z=collisions/sec
f=fraction of collisions that are effective
Arrhenius equation
k=Ae^-E/RT
k=rate constant
A=frequency factor
R=ideal gas constant
Frequency factor (A)
Measure of how often molecules in a certain reaction collide in s^-1
As temperature increases, what happens to rate constant
Increases, less negative exponent means more positive and larger
Transition state/Activated complex
Has greater energy than reactants or porducts
Transition state v. Reaction intermediate
Transition state is only theoretical
free energy change of the reaction
Difference between the free energy of products and reactants
Transition state between to products and to reactants
On either side of the transition peaks
What measures the concentration of gases of gas reactants
Partial pressures
Effect of temp on reaction rate
Almost always increases
Raising a reaction 10 C usually does what?
Double the rate of the reaction
Why would a polar solvent be preferred
Molecular dipole polarizes bonds of reactants
Homogenous catalysis
Catalyst is in the same phase as reactants
Heterogeneous catalysis
Catalyst is in a distinct phase
Do catalysts catalyze the reverse reactions?
Yes, by the same factor as forward
Do catalysts change Equilibrium or Keq?
No
Definition of rate
rate= -Delta[A]/aDelta(t)=-Delta[B[/bDelta(t)=+Delta(C)/cDelta(t)=+Delta[D]/dDelta(t)
Rate expressed as
Molarity/sec
Rate law=
k[A]^x[B]^y
x and y are experimentally determined orders of reaction, not coefficients
Overall order of reaction
Sum of x and y exponenets
When a rate determining step is given:
Stoichiometric coefficients on reactant side of rate-determining step are equal to orders of the reaction
Law of mass action
Equilbrium constant expression (must be used for a step that produced an intermediate)
Difference between equilibrium equation v. rate law
Rate law only has reactants
Keq for reversible reaction
=rate constant forward/rate constant backward
Is k really constant?
No, changes with temp and activation energy
How to calculate k
Substitue values into found rate law from any of the rows and solve for k
Zero order reaction
Change of concentration of reactants doesn’t change product formation only depends on k, temp, and catalyst
Rate of a reaction is __to slope
Opposite
= - slope
First order reaction
Directly proportional to only one reactant
What does the graph of a first order reaction look like
Curved
What does the graph of a zero order reaction look like?
Straight line
Second order reaction
Rate proportional to either concentrations of two reactants or square of a single reactant
How to turn a first order reaction into a straight line?
ln[A]
How to turn a second order reaction into a straight line?
1/[A]
Mixed order reactions
reactions that change order over time
Broken order
Reactions that have fractional orders
If a solution has a saturated catalyst, would adding reactants increase anything?
No
When finding rate law, the one held constant?
Is not the rate for that one
