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AQA A-Level Chemistry > Kinetics 2 > Flashcards

Kinetics 2 Flashcards

1
Q

What does the rate equation describe?

A

How the rate of reaction at a particular temperature depends on the concentration of the species involved

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2
Q

What is the rate of equation?

A

rate = k [A]* [B]*

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3
Q

Define autocatalysis

A

When a catalyst appears in the rate equation

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4
Q

What is an order?

A

The degree of effect to which change in a reactant has on rate

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5
Q

What does order zero mean?

A

A change in the concentration of the reactant has no effect on the rate

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6
Q

What does order one mean?

A

A change in the concentration of the reactant is directly proportional to change in the rate

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7
Q

What does order two mean?

A

A change in the concentration of the reactant is proportional to change in rate squared

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8
Q

How do the orders appear in the rate equation?

A

Order zero: does not appear
Order one: [A]
Order two: [B]2

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9
Q

What is the overall order of a reaction?

A

Sum of all the orders of the species involved in a reaction

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10
Q

How do you determine k from the rate equation?

A
  1. Determine the order of the reactants
  2. construct the rate equation
  3. rearrange for k
    rate/[a][B]
  4. determine units for k
  5. calculate value for k
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11
Q

Define rate of reaction

A

Change in concentration per unit time

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12
Q

What is the rate determining step?

A

The slowest step in a mechanism for a reaction

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13
Q

Are species involved only after the rate determining step in the rate equation?

A

No

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14
Q

What are the two rules involving the rate equation and the rate determining step?

A

-only species involved up and to including the RDS appear in the rate equation

  • must be enough of each species to fulfil the rate equation
  • –> ie: if rate=k[W]2[X] = all reactants up to RDS must have 2x W per X
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15
Q

What is the arrhenius equation?

word

A

The link between the rate constant, activation energy and temperature

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16
Q

What is the arrhenius equation?

Actual equation

A

k = Ae ^-Ea/RT

17
Q

Arrhenius equation: what is the exponential and what does it represent

A

e ^-Ea/RT

The fraction of collisions with enough energy to react

18
Q

What is the logarithmic form of the arrhenius equation?

A

ln(K) = -Ea/RT + ln(A)

19
Q

Why is the logarithmic form of the arrheius equation used?

A

It is easier to use the arrhenius equation when you take (natural) logs of both sides to the base e

20
Q

What does the logarithmic form of the arrhenius equation equate to?
hint: graphs

A

Equates to the equation of a straight line graph
ln(K) = -Ea/R x 1/t + ln(A)
Y = m x + c

21
Q

What is the effect of increasing the activation energy on the arrhenius equation and therefore rate of reaction?

A
  1. The fraction is larger and more negative
  2. t/4 the value of the exponential is smaller
  3. t/4 k is smaller
  4. t/4 decreased rate of reaction
22
Q

What is the effect of increasing the temperature on the arrhenius equation and therefore rate of reaction?

A
  1. The fraction is smaller and less negative
  2. t/4 the value of the exponential is bigger
  3. t/4 k is bigger
  4. t/4 increased rate of reaction
23
Q

Arrhenius equation with Ea as the subject

A

Ea = (ln(A)-ln(K)) (R x T)

24
Q

Arrhenius equation with T as the subject

A

T = Ea/ R x (lnA-lnK)

25
Q

Arrhenius equation with A as the subject

A

A = K/ e^ -(Ea/RT)

26
Q

What is the effect of concentration of a solution on. rate?

A

The higher the conc, the faster the reaction (unless zero order)

27
Q

Why does rate increase with conc of reactants?

A

The particles are closer together and so there are more frequent collisions

28
Q

What is the effect of surface area of a solid on rate?

A

The greater surface area, the faster the reaction

29
Q

Why does rate increase with surface area?

A

There are more particles exposed at the surface that can be collided with, and so there are more frequent successful collisions

30
Q

What is the effect of pressure of gases (reactants) on rate?

A

The higher the pressure, the faster the reaction (unless zero order)

31
Q

Why does rate increase with pressure of reactant gases?

A

The particles are closer together and so there are more frequent successful collisions

32
Q

What is the effect of temperature on rate?

A

The higher the temperature, the faster the reaction

33
Q

Why does rate increase with temperature?

3

A

Particles have more energy and so a greater proportion of the collisions are successful.

The particles also move faster and so collsions are more frequent.

Therefore, more frequent successful collisions

34
Q

What is the effect of a catalyst on rate?

A

A catalyst increases the rate of a reaction but is not used up

35
Q

Why does rate increase with a catalyst added?

A

It provides an alternative route/mechanism with a lower activation energy and therefore a greater proportion of the collisions are successful

AQA A-Level Chemistry (12 decks)

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