Section E Flashcards
What is the rate of reaction?
Rate at which reagents are used up and products are formed
What is the rate equation?
Rate = k[A]^m.[B]^n
How do you find overall order from partial order?
Overall order: m + n (if m or n are partial orders)
What does the rate constant vary with?
Temperature and the nature of reactants
Define a zero order reaction
Rate of the reaction does not depend on concentration
What is the equation for a zero order reaction?
[A] = [A0] - kt
In a zero order reaction, what decreases linearly over time?
Concentration of reactants
What is the equation for first order reactions?
[A] = [A0].e^-kt
Define T 1/2
Half life, time required for the concentration to drop to half of its original value
What is the equation to find half life from rate constant?
T 1/2 = ln2/k
what are the two processes occurring during drug metabolism?
Renal and metabolic elimination
What is the equation for drug metabolism kinetics?
-d[drugs]/dt = ae^-k1t + be^-k2t (k1/2 are diff. rate constants, a/b are weighting factors)
What form of kinetics is radioactive decay?
First order
What is the definition of radioactive activity (Bq)?
number of decay events per second
what are the units for radioactive activity?
Becquerels
What is 1 curie equivalent to?
3.7 x 10^10 disintegrations per second
What are 2 equations to find activity?
Activity = -dN/dt = kN
What is the equation for radioactive decay?
N = N0.e^-kt
What is an alternative equation for radioactive decay?
N = N0.e^(-ln2.t/t 1/2)
What is the half life of Krypton 85 gas?
10.8 years
Define a second order reaction
Rate of reaction proportional to square of concentration of the reagent
What is the equation for a second order reaction?
1/[A] = 1/[A0] + kt
What is the general procedure to measure a rate of reaction?
start reaction, measure property as function of time, convert measurement to concentration, analyse data
What spectrophotometric method is used to measure the rate of reaction for very fast reactions?
Flash photolysis
What spectrophotometric method is used to measure the rate of reaction for fast reactions?
Stopped flow method
How would you determine the order of a reaction experimentally?
diff. [A0] but same [B], plot [A] vs T (if linear then 0 order), plot ln[A] vs T (if linear then 1st order), plot 1/[A] vs T (if linear 2nd order)
What is the initial rates/differential method for determining order of a reaction?
keep [B] same, but [B]»>[A] so [B] constant, run reaction at different [A0], determine initial rate of each, plot against time, then put into equation: log(rate) = log(k obs) + alog[A]
What are pseudo-order conditions?
having such a high concentration of a substrate that it’s concentration remains effectively constant throughout the reaction
Define an elementary reaction
most reactions require several steps for the reaction to go to completion, reactions go via intermediates, two types e.g. photochemical reactions of alkanes
What is a unimolecular reaction?
Single species undergoes a change, type of elementary reaction, e.g. bond cleavage
What is a bimolecular reaction?
Two species come together, type of elementary reaction e.g bond formation
Define an elementary step
Reaction at molecular level e.g. collision between 2 molecules/bond breaking or formation
What is the equation for rate law in a unimolecular step?
Rate = k[A2] assuming reaction: A2 —> A + A
What is the equation for rate law in a homonuclear and bimolecular step?
Rate = k[A]^2 assuming reaction: A + A —> A2
What is the equation for rate law in a heteronuclear and bimolecular step?
Rate = k[A][B] assuming reaction: A + B —> AB
What is the rate determining step?
If reaction is a series of steps, then slowest step governs the rate of reaction,
What is the equation for rate constant from temperature?
k = Ae^-Ea/RT OR lnk = lnA - Ea/RT
What is the Arrhenius relation?
Rate constant depending on temperature, equation = k = Ae^-Ea/RT OR lnk = lnA - Ea/RT
Why do reactions depend on temperature?
depends on collisions, molecules require collision of threshold energy = activation energy
What is the Boltzmann distribution?
A distribution of the kinetic energy of molecules within a sample, represented by the equation e^-E/RT
What does the equation e^-E/RT represent?
The fraction of molecules at a temperature T which have energy greater than E
What is the significance of the pre-exponential factor A?
A usually represents the total number of collisions occurring per second in a reaction (if more complex then important to factor in orientation of collision)
Define a catalyst
A substance which takes part in a reaction and changes its rate but which can be recovered unchanged at the end of the reaction
Why do catalysts work?
Provides the reaction with a separate mechanism with a lower activation energy
What is a homogenous catalyst?
Catalyst in the same phase as the reactants
What is a heterogenous catalyst?
Catalyst in different phase as reactants
What is an example of an enzyme which shows extreme specificity?
Urease
Who proposed the lock and key method in 1958?
Koshland
What is the michealas-menten equation to find rate of product formed?
V = k2[E0][S]/(Km+[S])
What measure is km?
Measure of how strongly something binds, small Km = strong binding
What is the equation for Vmax?
Vmax = limiting rate = k2.[E0}
What is the equation for rate (V)?
V = Vmax.[S]/(Km+[S])
When does [S]+Km occur?
At very high [S]
What is the equation for Kcat?
Kcat = Vmax/[E0]
What is the definition of Kcat?
How many substrate molecules can be processed per second by 1mole of catalyst
What do you plot on a line weaver burke plot?
1/[S] (x) against 1/V (y)(double reciprocal plot)
What does the slope, X=0, Y=0 equal?
slope=Km/Vmax, X=0= -1/Km, Y=0= 1/Vmax
What is an Eadie-Hofstee plot?
rearrange v equation to: V = -V/[S].Km + Vmax, plot V against V/[S], Vmax at X=0, slope= -Km
What is a competitive inhibitor?
Inhibitor binds reversibly to active site, enzyme retains ability to process enzyme (Vmax same), but cannot bind S (Km changed) - gradient rotates up around 1/Vmax point
What is a non-competitive inhibitor?
Inhibitor binds to a remote site, affects its activity not ability to bind substrate so Vmax changes, Km same
What is an irreversible inhibitor?
Binds to active site and shuts down activity so [E] decreases
