Kinetics (all topics) Flashcards
Is the rate constant temperature dependent?
Yes, but independent of concentrations
What are some of the physical methods of monitoring reaction dynamics apart from monitoring concentration?
Monitor absorbance, conductance, laser excitation, pressure
According to Arrhenius what does a high Ea indicate?
A strong T dependance of the rate
What is the value of the gas constant, R?
8.314 JK-1mol-1
What information can we get form the graphical plot of the Arrhenius expression? What are the axes labels?
gradient = Ea/RT
y-intercept is lnA
link against 1/T
What is a fundamental principle of collision theory?
rate= collision frequency x fraction of collisions with sufficient energy
What new quantity does transition state theory define?
Free energy of activation
What is the method of integration for rate laws?
Graphical:
1st order: ln[A] vs t
2nd order: 1/[A] vs t
What assumption does pseudo order reaction theory make?
That the concentration of one of the reactants does not change considerably
Would the half life method graphically give a straight line or curve for 1st and 2nd order reactions?
1st: linear
2nd: curve
What theory does the isolation method for derivation of rate law make use of?
Pseudo order reaction theory
Describe the initial rate method for deriving rate constants and orders?
Vary [A] keep [B] and [C] constant. Ratios of rates can get experimental orders and then finally rate constant, k.
What are the units of the rate constant, k for 1st, 2nd and 3rd order reactions?
0 order: moldm^-3s^-1 1st: s^-1 2nd: mol^-1dm^3s^-1 3rd: mol^-2dm^6s^-1 (Can be derived by putting individual units in to rate law)
What are the 4 types of reactions we are concerned about for deriving rate data?
Reversible, pre-equilibrium followed by reaction, concurrent, consecutive
How can k1 and k-1 be calculated individually?
Temperature-jump relaxation method
For a concurrent reaction, what does the ratio of individual rate constants tell us?
Ratio of formation of individual products
What method can we use for reversible reactions to derive rate constants?
Distance from equilibrium graphical method. Method of integration can’t be used
What is the steady state approximation?
For k2»k1. Concentration of intermediate is found to achieve a constant value. dB/dt = 0
What are the steps in a radical chain reaction?
Initiation, propagation, retardation, branching, termination, inhibition.
What is the Lindemann mechanism?
Unimolecular collisions provide energy for the reaction. Activated molecules then react in a first order reaction
What are the two types of polymerisation?
stepwise and radical
According to Langmuir-Hinshelwood Kinetics what is the rate determining step in heterogenous catalysis reactions?
Surface reaction is RDS
What does Vmax represent in Michaelis-Menton kinetics?
Saturation of the enzyme
