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Medicinal Chemistry > Reaction Rates and Equilibria > Flashcards

Reaction Rates and Equilibria Flashcards

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1
Q

3 conditions required for a reaction to occur

A
  1. collision
  2. orientation: reactants must align properly to break and form bonds
  3. energy: the collision must provide the energy of activation
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2
Q

rate of the reaction equation

A

rate of reaction = change in concentration of reactant or product/ time

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3
Q

factors that affect the rate of reaction

A
  1. change in temperature
  2. change in reaction conc
  3. adding a catalyst
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4
Q

what happens to the rate of reaction when increasing the temperature

A

there is an increase in the KE of the reactant molecules, which makes them move faster, makes them collide more often, and makes them collide with more energy

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5
Q

what happens to the rate of reaction when increasing the reactant concentration

A

when there are more reacting molecules, more collisions that form products can occur and the reaction goes faster

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6
Q

what happens to the rate of reaction when you add a catalyst?

A

speeds up the rate of the reaction of both the forward and reverse reactions by the same amountsk by providing an alternative pathway that has a lower activation energy. As a result, more collisions provide sufficient energy for reactants to form product

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7
Q

activation energy

A

the minimum amount of energy required to break the bonds between atoms of the reactants

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8
Q

what happens to k as you decrease activation energy?

A

the smaller the Ea the larger the k

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9
Q

molecularity

A

the number of molecules that must collide to generate product

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10
Q

half-life in a chemical reaction

A

the time required to halve the reactant concentration

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11
Q

the half-life for a first-order reaction

A

t1/2 = ln2/k

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12
Q

the half-life for a second-order reaction

A

t1/2 = 1/k[A]0

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13
Q

dynamic equilibria

A

the reaction keeps happening both forward and reverse at the same rate

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14
Q

equilibrium conditions

A
  1. The rate of forward reaction is equal to the rate of the reverse reaction
  2. the forward and reverse reactions continue at the same rate
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15
Q

describe the properties of an equilibrium constant for a reversible chemical reaction

A
  1. it is a fixed value at a specific temperature
  2. the value that the system will evolve to reach an equilibrium
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16
Q

what is activity

A

the effective molar conc of a species in the solution

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17
Q

Kc

A

the numerical value obtained by substituting experimentally measured molar concentrations at equilibrium into the expression

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18
Q

large Kc

A

large amounts of products produced from the forward reaction

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19
Q

small Kc

A

low concentration of products and high concentration of reactants

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20
Q

reaction quotient Q

A

uses non-equilibrium concentrations

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21
Q

Q< Kc

A

more products will be synthesized

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22
Q

Q> Kc

A

the reaction proceeds to the left

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23
Q

le chatelier’s principle

A

when a stress is placed on a reaction at equilibrium the system responds by changing the rate of the forward or reverse reaction in the direction that relieves that stress

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24
Q

k -1

A

the kinetic rate of the reverse reaction

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25
Q

what is the relationship between the 2 rate constants of the forward and the reverse reaction?

A

k1/k-1 = Kc

the rate is numerically identical to the equilibrium constant

26
Q

what is Ea (forward) - Ea (reverse) equal to

A

E (forward) - E (reverse)

27
Q

what state do catalysts decrease?

A

the transition state

28
Q

what does oxygen transport involve

A

an equilibrium between hemoglobin Hb, oxygen, and oxyhemoglobin HbO2

29
Q

Chatelier’s principle of oxygen in water

A

oxygen is poorly soluble in water and so the equilibrium is in favour of the formatio of oxygen gas and not aqueous oxygen: the equilibrium shifts to the left

O2 + H2O (equilibrium sign) O2

30
Q

how can we perturb the equilibrium of oxygen in water

A

by addition of hemoglobin which gives rise to oxyhemoglobin: the concentration of oxygen that is free decreases because it is bound to haemoglobin

31
Q

what happens when there is a high pressure of oxygen in the alveoli

A

the reaction shifts in the direction of oxyhemoglobin

32
Q

what happens when there is a low pressure of oxygen in the tissues

A

the equilibrium shifts to release oxygen from HbO2

33
Q

what happens at normal Patm

A

oxygen diffuses into the blood because the partial pressure of oxygen in the alveoli is higher than in the blood.

34
Q

what happens at a decrease in Patm

A

results in a lower pressure of oxygen which means less oxygen is available for the blood and body tissues

35
Q

the equilibrium constant for hemoglobin

A

Keq = [HbO2]/[Hb]p^4 O2

oxygen gas binds with a 1: 4 stoichiometry (1Hb: 4O2)

36
Q

what happens at an altitude of 18,000ft

A

a person will obtain 29% less oxygen and may result in hypoxia

37
Q

hypoxia

A

respiratory rate, headache, fatigue

38
Q

what happens when there is a general decrease of oxygen in the air

A

the equilibrium will shift in the direction of the reactants thus depleting the conc of HbO2

39
Q

thermodynamics

A

measure of energies

40
Q

state variables

A

define the conditions of a reaction in regard with pressure, volume, temperature and chemical composition

41
Q

system

A

the reaction mixture we have: where the reaction takes place

42
Q

1st law of thermodynamics

A

the change of the internal energy of a closed system equals to the heat supplies to the system minus the work done by the system

43
Q

internal energy U

A

a state function that represents all the internal energy present in our reactants, products and molecules

44
Q

variation of internal energy of a state

A

ΔU = q + w

q= heat released/supplied by the system
w= work done on/by the system

45
Q

how can work be manifested in chemistry

A

by observing a change in volume

w = -pe ΔV

pe = external pressure

46
Q

what is the variation of enthalpy at a constant pressure equal to?

A

the heat exchange
ΔH = q

47
Q

enthalpy

A

comes from the combination of internal energy, pressure and volume and its variation is equal to heat.it is a state function and an extensive property

48
Q

extensive property

A

it depends on the state and size of the system

49
Q

what does the variation of enthalpy represent

A

the heat released or absorbed during a chemical reaction

50
Q

units of enthalpy

A

kJ/mol

51
Q

what does ΔHo mean

A

it is measured at the standard state (1atm, 298.15 K, and the solutions 1M)

52
Q

second law of thermodynamics

A

spontaneous processes are characterized by an increase in the disorder of the universe (entropy)

53
Q

what happens to the variation of entropy in spontaneous processes

A

the variation of entropy is equal or greater than the ratio between the heat exchange and teh temperature

ΔS > q/t

54
Q

when is a reaction spontaneous

A

ΔH - TΔS < 0

55
Q

free energy

A

state function introduced by gibbs and it refers to the energy exchanged throughout a chemical reaction

56
Q

equation for gibbs free energy

A

ΔG = ΔH - TΔS

57
Q

ΔG < 0

A

exergonic and it occurs spontaneously

58
Q

ΔG > 0

A

endergonic and it requires an external input of energy to occur

59
Q

variation in the free energy in a chemical reaction

A

ΔG = ΔGo + RTlnQ

60
Q

free energy variation knowing the equilibrium constant

A

ΔGo = -RTlnK

61
Q

equilibrium constant is temperature-dependent

A

lnk = -ΔH/R (1/T) + ΔS/R

62
Q

what needs to be overcome to reach the products

A

the transition state

Medicinal Chemistry (10 decks)

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