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Chemistry > Reaction Kinetics > Flashcards

Reaction Kinetics Flashcards

1
Q

What is the rate equation?

A

Rate = k[A]^a[B]^b , determined experimentally

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2
Q

Relationship between concentration and pressure?

A

Concentration directly proportional to pressure

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3
Q

What is zero-order reaction? Units of k?

A

Rate= k[A]^0 , mol dm-3 s-1

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4
Q

What is first-order reaction? Units of k?

A

Rate = k[A]^1 , s-1

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5
Q

Charactersitic of first-order reaction? Give two equations and an observation relating to this characteristic

A

Constant half-life

t1/2 = ln2/k
c/co = (1/2)^n

*Half-life is independent of concentration of reactants

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6
Q

What is second-order reaction? Units of k?

A

Rate = k [A]^2 , mol-1 dm3 s-1

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7
Q

Recall Concentration - Time graphs

A

Refer to Image 2

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8
Q

Recall Rate - Concentration graphs

A

Refer to Image 1

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9
Q

How to differ zero,first and second-order reactions?

A

Check shape concentration - time graphs.
Straight line –> Zero Order
Curve –> First or second –> Check the half life

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10
Q

Three conditions where pseudo-first-order reaction occurs. Common characteristic between them.

A
  1. Presence of large excess of reactants
  2. Reactant is a solvent (1)
  3. Presence of catalyst

[ ] approximately constant.

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11
Q

How to determine order from continuous method?

A

Shape of concentration time graph, check the half life

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12
Q

How to determine Rate Equation of first order reaction from continuous method?

A

Use t1/2 = ln2/k to find k

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13
Q

Given 2 sets of data, how to find order of reaction w.r.t to a reactant?

A

Initial rates method.

Initial rate = Gradient of graph at t=0min

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14
Q

How to determine order from discontinuous method?

A

Rate1/Rate2 = k[A]^a[B]b/ k[A]^a[B]b –> Solve

Compare 2 experiment where only 1 [reactant] changes

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15
Q

One characteristic about the slow step/ rate determing step

A

Has the highest activation energy

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16
Q

Three criteria to meet when proposing a reaction mechanism

A
  1. For slow step, aA + bB –> C ===> rate = [A]^a[B]^b
  2. All the elementary steps must add up to the overall balanced equation
  3. Rate equation should involve all the reactants in the overall balanced equation (Excluding intermediates)
17
Q

5 things to note when drawing Energy Profile diagram

A
  1. Correct axes (Energy,Reaction pathway)
  2. ___ Step Mechanism = ___ Peaks
  3. Slow step –> Highest Ea
  4. Endothermic vs Exothermic
  5. Label species (Start,intermediate,end)
18
Q

Maxwell Boltzmann Curve for increased temperature

A

Refer to image 3

  1. Start at origin
  2. Indicate T1 > T2
  3. Maximum curve shifts right and lowered
  4. Key
  5. Correct Axes
19
Q

Explain how increase in temperature increases rate of reaction.

A
  • Average KE of molecules increases
  • No. of reactant molecules with energy ≥ Ea increases
  • Frequency of effective collision increases
  • Rate constant K + Rate increases
20
Q

Maxwell Boltzmann Curve for presence of catalyst

A

Refer to image 4

  1. Start at origin
  2. Ea and Ea’
  3. Key
  4. Correct axes
21
Q

Explain how presence of catalyst increases rate of reaction.

A
  • Catalyst provides alternate pathway of lower Ea.
  • More molecules with energy ≥ lowered Ea (Ea’)
  • Frequency of effective collision increases
  • Rate constant K + Rate increase
22
Q

Define activation energy

A

Minimum energy needed by reactants for reaction to take place

23
Q

What are the 3 types of catalysis?

A
  1. Hetrogeneous
  2. Homogenous
  3. Autocatalysis
24
Q

How does hetrogeneous catalyst increase rate?

2 ways

A
  • Adsorption increases concentration of reactant

- Adsorption weakens exisiting bonds within reactant molecules, lowers Ea

25
Q

Kinda explain homogeneous catalysis

A

Converted into reactive intermediate to take part in reaction, regenerated afterwards

26
Q

What is autocatalysis?

Explain the charactersitics of autocatalysed reaction. (4 points)

A

Products formed acts as catalyst

  1. Initially slow
  2. Rate increases as product (autocatalyst) formed
  3. Rate reaches max
  4. Rate decreases towards end as concentration of reaction decrease. Reaction stops when reactant used up.
27
Q

Condition for maximum rate of enzyme-substrate reaction

A

All active sites of enzyme occupied by substrate

28
Q

When and why is rate first order wrt substrate?

Rate - [substrate] graph

A

Initially, when active sites of enzyme not fully occupied

29
Q

When and why is rate zero order wrt substrate?

Rate - [substrate] graph

A

After certain concentration, when active sites of enzyme occupied

30
Q

Using the inital rates method when given volume

One thing to note when changing total volume

A

Make sure total volume of solution is same, volume directly proportional to concentration

  • Rate does not change when changing total volume*
  • -> Concentration remains the same

Chemistry (5 decks)

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