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Chemistry (S2) > 2.3 Knetics > Flashcards

2.3 Knetics Flashcards

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1
Q

What is rate in chemical reactions?

A

Change in concentration of a species over time

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2
Q

What is the concentration unit?

A

mol/ L OR M

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3
Q

What is the time unit?

A

seconds

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4
Q

Rate units

A

M/s

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5
Q

Activation energy

A

Minimum energy required to initiate a chemical reaction

Difference between reactants and the transition state (on graph)

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6
Q

What is the highest point on a reaction coordinate diagram?

A

Transition state

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7
Q

What shows the energy change of a reaction, on a graph

A

Difference between reactants and products

ΔH if enthalpy

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8
Q

Area under maxwell boltzmann distribution = ?

A

Total number of particles

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9
Q

What happens to maxwell boltzmann distribution hen temperature is INCREASED?

A
  • curve shifts to right
  • maximum point / mean value is lower and further to right
  • smaller number of particles with low energy
  • larger number of particles with energy > Ea (Ea stays same)
  • More successful collisions
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10
Q

What does adding catalyst do to maxwell boltzmann distribution?

A
  • Lowers Ea (further to right)
  • more particles with energy > Ea
  • ∴ rate of reaction increases
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11
Q

How do catalysts speed up reaction?

A

Form an alternative reaction pathway

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12
Q

What does Km show?

A

How effectively an enzyme can bind to its substrate

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13
Q

What does Vmax show?

A

How efficient the enzyme is at catalysing the reaction

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14
Q

What do 0 orders depend on?

A

Depend on a saturatable enzyme or a saturatable catalyst

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15
Q

Increased surface area …………… rate of reaction

A

Increases

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16
Q

Why are many powdered substances (eg. Flour) highly flammable?

A
  • carbohydrates with lots of C H and O
  • Have a very high SA
  • Burn very rapidly if Ea is reached
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17
Q

Increasing pressure …………….., the rate of reaction

A

Increases

NOTE: Apart from 0 order reactions (eg. When enzyme is saturated)

18
Q

What is the general rate equation of a reaction?

A

rate = K [A]* × [B]*

  • = power = order wrt agent
19
Q

Σ powers in a rate equation =

A

Overall order of reaction

20
Q

What is K in rate equation?

A

K = Ae ^(Ea/RT)

A = likelihood of collisions being in correct lineup
R = gas constant
T = Temperature in k

21
Q

What determines the rate equation?

A

Slowest step

This has the slowest rate constant (k)

22
Q

In zero order reactions, rate is equal to….?

A

Rate = K

23
Q

What are characteristics of a 0 order concentration time graph

A
  • straight linear line
  • gradient = -k
24
Q

In zero order reactions, the rate is independent to…..

A

The concentration of reactant

25
Q

In first order reactions, the rate is….

A

Proportional to the concentration of a single reactant raised to the first power

26
Q

What is the shape of a concentration time graph of a first order reaction?

A

Curve

Doing the log of the graph will give you a straight line graph

27
Q

In first order reactions, the half lives are….

A

Constant

They depend in the rate constant K

28
Q

What is half life?

A

The time taken for the concentration of a reactant to drop to half its original value

29
Q

In zero order reactions, the half lives….

A

Get shorter

30
Q

In higher order reactions, the half lives…..

A

Get longer

31
Q

What is the sum of exponents in a second order reaction?

A

2

32
Q

What shape are lines of different orders in graphs with rate against concentration?

A

0 - straight line parallel to x axis

1st - linear (rate is proportional to concentration) (gradient = k)

2rd - exponential (rate =k²)

33
Q

What is molecularity?

A

The number of individual molecules taking part in the rate determining step

34
Q

Unimolecular rate determining step =

A

Rate = k[A]

35
Q

Biomolecular rate determining steps =

A

Rate = k[A]²

Rate = k[A][B]

36
Q

Trimolecular rate determining steps =

A

Rate = k[A]³

Rate = k[A]²[B]

Rate = k[A][B][C]

37
Q

What can make the same starting materials form different products, in organic and enzyme chemistry?

A

Different reaction conditions

Must be reversible reaction
2 possible sets of products with different energies

38
Q

What is the thermodynamic product of a reaction?

A

One that takes the system to the most stable state

39
Q

What is used to get to thermodynamic products?

A

High reaction temperatures

Long reaction times

40
Q

What is the kinetic product?

A

The one that’s fastest to get to
Ans has the lowest Ea

41
Q

What conditions used to form kinetic products?

A

Low temperature
Short reaction times

42
Q

Which species appear in rate equation?

A

Everything upto and including the rate determining step

Chemistry (S2) (9 decks)

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