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Physical Chemistry > Reaction Rate, Reaction Order & Rate constant > Flashcards

Reaction Rate, Reaction Order & Rate constant Flashcards

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1
Q

What do reaction mechanisms consist of?

A

A series of elementary reaction steps that make up the overall reaction.

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2
Q

What is the rate of reaction expressed as?

A

A change of the concentration of a given reactant (or product) as a function of time:

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3
Q

What factors influence the rate of reaction?

A
  1. Concentration of reactants
  2. Temperature and pressure of the
  3. Solvent (polarity, ionic strength)
  4. Surface area of a solid reactant
  5. Action of catalysts
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4
Q

What is the rate law?

A

Relation between rate reaction and the reactant concentration

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5
Q

What is the rate constant dependent on?

A

Independent of concentrations but depends on T or P. Units depends on the overall order of the reaction

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6
Q

What is the rate law of a zero-order reaction?

A

Reaction proceeds at constant arte and is independent of the reaction concentration

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7
Q

What are the units of k for a zero-order reaction?

A

Concentration.time-1

mol.L-1.s-1

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8
Q

What is half-life?

A

The half (t1/2) of a reaction is the time taken for the concentration of reactant to fall to half of its original value

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9
Q

What is the shell-life (t0.9 or t10%)?

A

Is the length of time the product may safety be stored on the dispensary shelf before significant decomposition occur. It is the time taken for decomposition of 10% of the active drug to occur

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10
Q

What is the rate law of a first order reaction?

A

Rate depends on the concentration of one reactant

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11
Q

What are the unit of a first- order reaction?

A

Units of k: time-1

s-1 (or similar)

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12
Q

What is the plot of the logarithms of the concentration of the analyse (as ordinate) against time (as abscess) for a zero and first order reaction?

A

Linear with a gradient of -k

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13
Q

What is the rate constant in a second-order type I reaction?

A

Rate depend on the product of two concentration terms which refer to same reactant

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14
Q

What are units of k for a second order type I reaction?

A

Concentration-1.time-1

L.mol-1.s-1 (or similar)

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15
Q

What is the plot of the inverse of the concentration of the analyse (as ordinate) against time (as abscess) for a second order type I reaction?

A

Linear with a gradient of k

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16
Q

What is the rate law for a second order reaction type II?

A

Rate depends on the product of two concentration terms

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17
Q

What is Pseudo first order?

A

Rate depends on the concentration of one reactant

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18
Q

What are the units for a second order reaction?

A

Units of k: time-1

Ex: s-1

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19
Q

What are the units of Ea?

A

J.mol-1 (R= 8.31 J.K-1)

20
Q

What are the units of T?

A

K

21
Q

What are the units of A?

A

Units of the rate constant

22
Q

What is happens to the half-life for n=0?

A

It increases with increasing concentration

23
Q

What happens to the half-life for n=1?

A

It does not change with change in concentration

24
Q

What happens to the half-life for n=2?

A

Decreases with increasing concentration

25
Q

What must reactant molecules do in order to react?

A

Must collide with the appropriate orientation and with a minimum energy

26
Q

What is activation energy?

A

Minimum energy needed for the reaction to occur. Ea comes from the thermal excitation of molecules

27
Q

What does a large Ea mean?

A

Strong T dependence and a slow reaction

28
Q

What does a small Ea mean?

A

Weak T dependence and a fast reaction

29
Q

What is a catalyst?

A

Speeds up a reaction by providing an alternate reaction mechanism with a lower energy of activation compare to the unanalysed pathway

30
Q

How is the rate changed?

A

By lowering Ea

31
Q

What can enzymes do to a reaction rate?

A

Increase the A factor

Decrease the energy of activation. Increase the reaction rate without increasing the temperature

32
Q

What mechanism describes the behaviour of many enzymes?

A

Michaelis-Mennen mechanism

33
Q

What is Km?

A

A constant. It is the concentration of substrate [S] required to reach half-maximal velocity (Vmax/2). Under true conditions it is the estimate of the dissociation constant of the ES complex

34
Q

What does a small Km mean?

A

Tight binding between E and S

35
Q

What does a large Km mean?

A

Weak binding between E and S

36
Q

What is Vmax?

A

A constant. Is the theoretical maximal rate of the reaction but it is never achieved in reality. Vmax is asymptotically approached as substrate is increased.

37
Q

What would need to be required to reach Vmax?

A

All enzymes molecules to be tightly bound with substrate

38
Q

What is kcat?

A

Turnover number. It is the number of substrate molecules converted to product per unit of time and per enzyme molecule (when E is saturated with S). It a measure of the catalytic activity of the enzyme

39
Q

What is kcat/Km?

A

The catalytic efficiency. It is an estimate of “how perfect” the enzyme is. It is used to rank enzymes

40
Q

What does a big kcat/Km mean?

A

That an substrate binds tightly to E (small Km), with a fast reaction of ES complex.

41
Q

What is reversible competitive inhibition?

A

The substrate and the inhibitor are chemically similar. S and I compete for binding to the same active site: S and I cannot bind to the enzyme at the same time

42
Q

What can overcome reversible competitive inhibition?

A

Increasing [S]

43
Q

What happens to the constants in reversible competitive inhibition?

A 
Maximum velocity (Vmax) unchanged
Km is increased
44
Q

What is non competitive inhibition?

A

When the substrate and the inhibitor are not similar. I does not bind to the active site of the enzyme. I binds equally well to both free E and the enzyme-substrate complex. Increasing [S] cannot overcome inhibition

45
Q

What happens to the constants in reversible non competitive inhibition?

A

Km unchanged

Vmax is decreased

Physical Chemistry (6 decks)

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