Chapter 22 Reaction kinetics Flashcards
Define rate equation
An equation showing the relationship between the rate constant, and the concentrations of the species that affect the rate of reaction.
Define order of reaction (and overall order)
The power to which the concentration of the reactant is raised in the rate equation. The overall order of reaction is the sum of these powers.
Define rate constant
The proportionality constant, k, in a rate equation. e.g. rate= k[NO]².
Define half life (t¹/₂)
The time taken for the concentration of the limiting reactant in a reaction to decrease to half its initial value.
What is the rate-determining step?
The slowest step in a reaction mechanism.
How to write rate equation for a multi-step reaction?
Only include the concentrations of the slow step reactants according to their stochiometry numbers IN THE SLOW STEP. Also, do not include intermediates in the rate equation.
What cannot be part of rate equation?
Indermediates (instead if the intermediate is part of the slow step, you have to include the constituents of the intermediate into the rate equation).
Define intermediate
A reaction intermediate is transient species within a multi-step reaction mechanism that is produced in the preceding step and consumed in a subsequent step to ultimately generate the final reaction product.
Define homogenous catalysts
Catalysts that are in the same phase as the reactants.
Define heterogenous catalysts
Catalysts that are in different phases as the reactants.
t¹/₂= ?
t¹/₂= 0.693/k (only for 1st order)
Describe the mechanism of heterogenous catalysis
Diffusion of reactants onto catalyst surface, adsorption to catalyst surface, reaction, desorption from catalyst surface, diffusion of products away from catalyst.
What does rate order 0 indicate?
r=k. Concentration of that reactant has no effect on the rate.
What does rate order 1 indicate?
r=k[B]. Concentration of that reactant has a proportional effect on the rate. y=mx graph.
What does rate order 2 indicate?
r=k[C]². Concentration of that reactant has a more than 1:1 proportional effect on the rate. y=mx² graph.
Shape of concentration-time graph for order 0
Straight line down.
Shape of concentration-time graph for order 1
Curve down below the straight line of order 0.
Shape of concentration-time graph for order 2
Curve down below the curve of order 1.
Half-life of order 0 graph…
decreases.
Half-life of order 1 graph…
remains constant throughout.
Half-life of order 2 graph…
increases.
lnk= ?
lnk= lnA - Eₐ/RT [lnk= (-Eₐ/RT) ¹/T + lnA]
Hetereogenous catalysis 2 examples
Iron powder in haber process and platinum catalytic converter.
