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Chemistry > Rate Equations > Flashcards

Rate Equations Flashcards

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1
Q

Rate of reaction

A

The change is concentration of a substance in a given time

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2
Q

Units of rate

A

Moldm-3s-1

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3
Q

Reactions can only occur when…

A

Collisions take place between particles having sufficient energy

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4
Q

What is the sufficient energy called

A

Activation energy

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5
Q

Activation energy

A

The minimum energy required to start a reaction by the breaking of bonds

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6
Q

How does increasing conc increase rate of reaction

A
  • more particles in given volume

- more frequent successful collisions

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7
Q

How does increasing pressure increase rate

A
  • increasing pressure means same particles in a smaller volume
  • more frequent successful collisions
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8
Q

How does increasing SA of a solid increase rate

A

Powders increase SA- more frequent successful collisions

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9
Q

How does increasing temp increase rate

A

(Maxwell Boltzmann) more particles with energy equal to or greater than Ea so more successful collisions

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10
Q

How does a catalyst increase rate

A

Provides alternative pathway with lower Ea so far more molecules have Energy equal to or greater than activation energy

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11
Q

what does the rate equation show

A

the relationship between the rate of a reaction and the initial conc of the reactants

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12
Q

general rate equation

A

rate= k[A]m [B]n

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13
Q

what is [A] in rate equation

A

conc of A

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14
Q

what is [B] in rate equation

A

conc of B

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15
Q

what is m in rate equation

A

order with respect to A

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16
Q

what is n in rate equation

A

order with respect to B

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17
Q

what is k in rate equation

A

rate constant

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18
Q

what is the overall order of a reaction

A

the sum of the individual orders

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19
Q

half life

A

the time taken for the concentration of a reactant to half

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20
Q

how would zero order be shown on a conc-time graph

A

straight line indicating uniform day

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21
Q

how would first order be shown on a conc time graph

A

curve- equal half lives

22
Q

how would second order be shown on a conc time graph

A

steeper curve- half lives increase

23
Q

what is the gradient at a particular time on a conc time graph a measure of

A

the rate at that time

24
Q

how to determine order of ror with a conc time graph

A
  • start with known conc of a and b
  • ensure conc of one (b) is much larger than other- remains constant
  • determine conc of A at different times
  • plot graph
  • continuous monitoring method
25
Q

how can rate-conc graph be plotted

A
  • conc-time graph plotted
  • tangents drawn, giving ror values
  • rate-conc graph plotted
26
Q

rate graph zero order

A

flat line

27
Q

rate graph first order

A

straight diagonal line, positive gradient

28
Q

rate graph second order

A

curve

29
Q

what is k

A

a proportionality constant that links rate of reaction with the concentrations of reactants

30
Q

correlation between value of k and rate

A

k larger- faster rate

31
Q

what do the units of k depend on

A

overall order of reaction

32
Q

what do chemical reactions often take place in

A

a series of steps called the reaction mechanism

33
Q

what can the rate equation provide clues about

A

a likely reaction mechanism by identifying slowest stage of a reaction sequence

34
Q

rate determining step

A

slowest step in a reaction mechanism

35
Q

what will any step that occurs after rate determining step not affect

A

overall rate- reactants involved in later steps wont appear in rate equation

36
Q

how can you tell if the reaction is a one step process

A

the powers in the rate equation match the stoicheometry of the overall equation

37
Q

how can you tell if the reaction has more than one step

A

the powers of the rate equation don’t match the overall equation

38
Q

what always increases when temperature is increased

A

the rate of reaction- Maxwell districution

39
Q

if the temperature is increased in a reaction, why must k increase as rate increases

A

if [A] and [B] are kept constant k must increase

rate=k[A]m[B]n

40
Q

what is the increase of k with temperature

A

exponential

41
Q

what is the relationship between rate constant and temp described by and what does it allow us to work out

A

Arrhenius equation

allows us to work out Ea

42
Q

the Arrhenius equation

A

k=Ae^-Ea/RT

43
Q

what does k mean in Arrhenius equation

A

rate constant

44
Q

what does A mean in Arrhenius equation

A

Arrhenius constant

45
Q

what does ea mean in Arrhenius equation and units

A

activation energy (J)

46
Q

what does R mean in Arrhenius equation

A

ideal gas constant

47
Q

what does t mean in Arrhenius equation and units

A

temperature (K)

48
Q

how can the Arrhenius equation be rearranged

A

by taking the natural log (ln) of both sides

49
Q

Arrhenius equation rearranged

A

lnK=lnA -Ea/RT

50
Q

what form can rearranged Arrhenius equation rearranged be expressed in

A

y=mx+c

51
Q

how can Arrhenius equation be used to determine the activation energy of a reaction

A
  • k can be determined at different temperatures
  • graph poltted with k on y axis and 1/T on x axis
  • line of best fit is a straight line and so can be described as y=mx+c

Chemistry (42 decks)

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