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Reaction Toolkit > Ces (L10-L14) > Flashcards

Ces (L10-L14) Flashcards

1
Q

how to define rate?

A

the rate of change of concentration of a specified reactant

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2
Q

how to find the rate of reaction at a specific point in the reaction coordinate?

A

tangent of the curve

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3
Q

what is the general equation for rate of reaction v? wht what are the units

A

v = 1/stoic coe of substance x dconc / dt

eg. v = 1/2 (d[A]/dt)

add a negative for reactant and positive for product

mol L-1 S-1

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4
Q

define the rate law

A

expression of the rate of reaction in terms of concentrations of reactants, products and catalysts but not intermediates

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5
Q

what are examples of ways to measure the rate law?

A

pressure, volume, conductivity, pH, flourescence…

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6
Q

what is the issue with real time analysis?

A

limited by the response rate of the detector

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7
Q

what is quenching a reaction?

A

reaction is stopped by cooling, diluting etc. after reacting for a certain period of time and solution is then examined (through mass spec or chromatography)

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8
Q

what are the equations for beer lambert?

A

T = final/ initial
A = ecl = -logT

units for e are dm^3 mo^-1 cm^-1

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9
Q

what is the half life equation for a first order reaction?

A

t1/2 = ln2/k
no concentration dependence

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10
Q

what is the reaction time constant equation and what does it measure?

A

the time required for the initial concentration of a reactant to fall to 1/e of its initial concentration so A0/e)

t = 1/k

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11
Q

what is the half life for a second order reaction?

A

t1/2 = 1/k[A]0

there is a dependence on the initial concentration (lower concentrations = longer half life)

if half life is not constant then it could be a second order reaction

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12
Q

how to prove that the order of reaction is correct using graphical methods?

A

plot the graph in the format y=mx+c where its conc A = kt + initial conc

or plot half life graph if you are sure that the reaction is 1st order

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13
Q

define rate constant

A

no. of successful collisions per unit time

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14
Q

what are the 2 arrhenius paramters and what do they represent?

A

A = no. of total collisions (whether they are successful or not)

Ea= activation energy (a measure of the fraction of collisions that are successful)

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15
Q

what is the equation to plot the graph for arrhenius equation?

A

lnk = lnA - (Ea/RT)

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16
Q

in a 2 step reaction, what determines how long an intermediate lives? which rate constant is bigger normally?

A

the size of the rate constants of the intermediate being produced and consumed

normally rate constant of consumption is much higher than rate constant of production

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17
Q

what is the pre-equilibrium rate equation?

A

v = kb (ka/ka reverse) [A][B]

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18
Q

what is steady state approximation?

A

the intermediate is consumed as fast as it is produced, thus the gradient of its curve it close to 0.

it can be assumed that the rate of change of concentration of an intermediate is approximately 0

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19
Q

what does e^ negative infinity go to?

A

0

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20
Q

what is the lindemann-hinshelwood mechanism? what are its limitations?

A

a reaction can be first or second order depending on the pressure

does not recognise that a specific excitation (to get correct geometry etc.) may be required at high pressures before the reaction occurs (excited state does not always auto make products)

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21
Q

what is an alternate model to the LH theory and what does it take into account?

A

RRK model which takes into account that the reaction will only occur when enough of the energy in a model has migrated to a particular location (eg. vibrational excitation) in order for a reaction to occur

22
Q

why do enzyme bound substrate react faster?

A

the activation energy for a reaction of an enzyme-bound substrate is lower than a free substrate because the binding interaction shifts the substrate geometry closer to the transition state

23
Q

what are the 2 enzyme models and what are their differences?

A

lock and key: complementary 3D structure between active site and substrate (no major structural change)

induced fit: active site goes through conformational change during binding of substrate (substrate fits well after this change)

24
Q

what does vmax indicate?

A

maximum rate of reaction between enzyme and substrate because all available enzyme molecules are bound to substrate molecules and rate becomes independent of substrate concentration

25
Q

draw a graph of enzyme activity

A

check L13 S8

26
Q

what are the 3 steps possible in an enzyme mechanism?

A
  1. k1 which is E + S -> ES
  2. k-1 which is ES -> E + S
  3. k2 which is ES -> P + E

*first 2 steps are reversible

27
Q

what is the equation for michaelis constant

A

Km = (k-1 + k2) / k1

28
Q

what does vmax equal to?

A

vmax = k2 x [total enzyme concentration]

29
Q

what is the rate law for an enzyme written as?

A

v = (vmax[S])/(kM + [S])

30
Q

what is the rate at low and high concentrations of substrate?

A

high concentrations v = vmax

low concentrations = (vmax[S])/Km

31
Q

what does KM value represent?

A

the substrate concentration at which the rate of half of the maximum value

-> an indication of the enzyme affinity to the substrate (higher affinity means lower concentration of substrate needed)
-> not effected by concentration of enzyme but a property of an enzyme (thus enzyme dependent)

32
Q

what doe k2 in enzyme reaction indicate?

A

turnover number: the maximum number of molecules of substrate that each molecule of enzyme can turn to products per second

33
Q

draw a lineweaver burk plot and label everything and what the indicate?

A

check L13 S14

34
Q

name the 2 types of inhibition and what they do

A

competitive inhibition: similar structure to the substrate so it competes for the active site and increases KM (ability of enzyme to bind to substrate)
-> affinity of substrate to enzyme active site decreases cause there are more options for the enzyme to bind to other things

non-competitive inhibition: binds to allosteric site, does not effect ability of substrate to bind to active site but effects whether the substrate can form products after binding )
-> effects activity of enzyme thus changes Vmax

35
Q

what is the 3 components for the rate of a bimolecular reaction?

A

v = collision rate x energy requirement x steric requirement

36
Q

what are the 2 assumptions for the collision tube?

A
  • anything that is less than half d distance away will result in a collision
  • mobile molecule travels through the gas with a mean relative speed vrel
37
Q

what is a collision cross section?

A

area of the collision tube that shows if a molecule will collide with the mobile molecule

38
Q

what is number density?

A

no. of molecules per unit volume of space

39
Q

what is the collision frequency equation and explain how it is derived?

A

z = sigma x vrel x number density

before there is delta time but then collision frequency is per unit time divide by delta time and it disappears

the frequency of reactions within a volume of space

40
Q

what is the collision density equation?

A

ZAB = sigma x relative speed x ND of B x ND of A

41
Q

how do you find the collision cross section with molecules of difference sizes?

A

d = 1/2 (dA + dB)

42
Q

what is the expression for collision rate?

A

ZAB = sigma x v rel x avo constant ^2 x [A] x [B]

43
Q

what is the relationship between avogadros constant, molar gas constant and boltzmann distribution constant?

A

R = k x NA

44
Q

what is the collision frequency equation in terms of pressure and temperature (derive from number density equation)

A

z = (sigma x vrel x P)/ (boltzmann x T)

45
Q

what are the 3 assumptions in the theory of gases?

A
  1. random motion of gas molecules of mass m and diameter d
  2. size of molecules is negligible compared to the distances they travel
  3. perfectly elastic collisions only (total translational kinetic energy is conserved)
46
Q

how to find the average PDF style?

A

sum of frequency of x x probability of x

47
Q

what is the relative speed equation?

A

vrel = (8RT/pi x reduced mass)^1/2

48
Q

what is the steric requirement for a reaction to occur and what is the range of values?

A

orientation represented by P

can range from 1 (all orientations lead to a reaction) and 0 (no orientations lead to a reaction)

49
Q

what is the harpoon mechanism?

A

electron transfer means that two ions are formed and coulombic attraction moves them closer together, the electron does not have to be touching to be transferred therefore the value of P (for the collision tube) can be greater than 1

50
Q

what are some limitations of collision theory? what can be used instead

A

assumes that all kinetic energy is available for reaction (this is only true for head on collision)

collision theory ignores energy stored in vibrational and rotational energy states

transition state theory is better (more detail for rate constant calculations)

Reaction Toolkit (2 decks)

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