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chemistry > 5.1.1 rates of reaction > Flashcards

5.1.1 rates of reaction Flashcards

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1
Q

what is the rate of reaction?

A

the change in concentration of a reactant or a product in a given time

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2
Q

what is the order of reaction?

A

the power to which the concentration of a reactant is raised in the rate equation

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3
Q

what is the overall order?

A

the sum of individual orders of reactants in the rate equation

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4
Q

what is zero order?

A

the concentration of a reactant has no effect on the rate

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5
Q

what is first order?

A

a reaction is first order with respect to a reactant when the rate depends on its concentration raised to the power of one

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6
Q

what is second order?

A

a reaction is second order with respect to a reactant when the rate depends on its concentration raised to the power of two

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7
Q

rate equation for reaction: A + B → C with orders x for A and n for B

A

rate = k [A]ˣ [B]ⁿ

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8
Q

how are orders of reactions found?

A

from experimental results - compare concentration change with change in initial rate

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9
Q

what is shape of a concentration-time graph for a zero order reaction?

A

a straight line with a negative gradient

- the value of the gradient is equal to the rate constant k

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10
Q

what is shape of a concentration-time graph for a first order reaction?

A

a downward curve with a decreasing gradient

- the time for the concentration of the reactant to halve is constant (constant half lives)

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11
Q

what is shape of a concentration-time graph for a second order reaction?

A

a downward curve with a decreasing gradient, steeper than the downward curve of a first order reaction

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12
Q

what is a half-life?

A

the time taken for the concentration of a reactant to decrease by half

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13
Q

how to determine k for a first order reaction? method 1

A

calculating the rate constant from the rate

  • tangent to curve is drawn
  • gradient of tangent is calculated = rate
  • k calculated by rearranging the rate equation
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14
Q

how to determine k for a first order reaction? method 2

A

calculating the rate constant from the half-life

  • uses exponential relationship for a constant half-life
  • k = ln2 / t(half-life)
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15
Q

what is shape of a rate-concentration graph for a zero order reaction?

A

a horizontal straight line with no gradient

  • y intercept gives rate constant k
  • reaction rate doesn’t change with increasing concentration
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16
Q

what is shape of a rate-concentration graph for a first order reaction?

A

a straight line through the origin

  • rate is directly proportional to concentration
  • the gradient is equal to the rate constant
17
Q

what is shape of a rate-concentration graph for a second order reaction?

A

a upward curve with increasing gradient
- k can be found by plotting another graph of rate against concentration squared, producing a straight line graph through origin - k is equal to gradient

18
Q

what is a clock reaction?

A

the time t from the start of an experiment is measured for a visual change top be observed (colour or precipitate)

  • initial rate proportional to 1/t
  • repeated at different concentrations
  • a graph of 1/t against concentration is plotted
19
Q

what are methods of continuous monitoring?

A
  • monitoring by gas collection
  • monitoring by mass loss
  • colorimetry - the amount of light absorbed by a solution is measured
20
Q

what is continuous monitoring used for?

A

to plot concentration-time graphs

21
Q

how accurate are clock reactions?

A
  • reasonably accurate provided less than 15% of the reaction has taken place
22
Q

what is the rate-determining step?

A

the slowest step in the reaction mechanism of a multi-step reaction

23
Q

what does the rate equation show about the rate determining step?

A

the orders show the number of species in the rate determining step

24
Q

what factors affect the rate constant as temperature increases?

A
  • increasing temperature shifts Boltzmann distribution to right, increasing the proportion of particles that exceed the activation energy
  • particles move faster and collide more frequently
25
Q

what is the Arrhenius equation?

A

the exponential relationship between the rate constant k and temperature T
k = A e^(- Ea/RT)

26
Q

what does the exponential factor e^(- Ea/RT) represent?

A

the proportion of molecules that exceed Ea and that have sufficient energy for a reaction to take place

27
Q

what does the pre-exponential term A represent?

A

takes into account he frequency of collisions with the correct orientation

28
Q

what is the logarithmic form of the Arrhenius equation?

A

ln k = -Ea/RT + ln A

29
Q

how is the logarithmic Arrhenius equation shown graphically?

A

plot ln k against 1/T

- downwards straight line with gradient of -Ea/R and y intercept of ln A

chemistry (39 decks)

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