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A Level Physical Chemistry > Section 5 - Kinetics, Equilibria and Redox Reactions > Flashcards

Section 5 - Kinetics, Equilibria and Redox Reactions Flashcards

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1
Q

Define reaction rate

A

Change in concentration/amount of a reactant or product over time.

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2
Q

What is the formula for rate of reaction?

A

Amount of R used or P formed/time

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3
Q

What are the two conditions that allow a reaction to take place when particles collide?

A
  • right direction - activation energy
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4
Q

Define activation energy

A

Minimum amount of kinetic energy required for particles to react upon collision.

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5
Q

What does a Maxwell-Boltzmann distribution show?

A

The number of molecules in a gas against their kinetic energy.

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6
Q

What is the area under a Maxwell-Boltzmann distribution?

A

The total number of molecules.

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7
Q

Why does a Maxwell-Boltzmann curve start at (0,0)?

A

0 molecules will have 0 energy

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8
Q

What does the peak of the Maxwell-Boltzmann curve show?

A

The most probable energy of any molecule.

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9
Q

Where is the mean energy of all of the molecules in a Maxwell-Boltzmann curve?

A

Slightly to the right of the peak.

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10
Q

Where would you find the section of molecules with the required activation energy on a Maxwell-Boltzmann curve?

A

On the right.

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11
Q

What happens to the average kinetic energy if the temperature of a reaction is increased?

A

It will increase.

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12
Q

What happens to the proportion of molecules with the required activation energy if the temperature of a reaction is increased?

A

It will increase.

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13
Q

How does the Maxwell-Boltzmann curve change when temp is increased?

A
  • shifts to right - peak is smaller
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14
Q

Why does rate of reaction increase with temp?

A
  • molecules have more energy - more have Ea required - move faster - collide more often - more likely to react
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15
Q

Why does rate of reaction increase with concentration?

A
  • particles closer together - collide more often - more likely to react
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16
Q

Why does rate of reaction increase with pressure?

A
  • particles closer together - collide more often - more likely to react
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17
Q

Why does rate of reaction increase with a catalyst?

A
  • provide alternative route with lower Ea - more particles have enough energy to react - more likely to react
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18
Q

Define catalyst

A

A substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower Ea. It is chemically unchanged at the end of the reaction.

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19
Q

Why are catalysts good in industry?

A
  • don’t get used up (small amount required) - work faster - allow a lower temp
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20
Q

Give 3 ways to measure reaction rates:

A

1) Timing how long a precipitate takes to form 2) Measure a change in mass 3) Measure vol of gas given off

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21
Q

Give a negative of timing how long a precipitate takes to form

A

Subjective

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22
Q

Give a pro and con of measuring a change in mass

A

+ accurate and easy - releases gas

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23
Q

Give a pro and con of measuring vol of gas given off

A

+ accurate - only works if one or more product is gaseous

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24
Q

Give an example of a reaction that forms a precipitate

A

Sodium Thiosulfate and Hydrochloric Acid

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25
Q

What do Sodium Thiosulfate and Hydrochloric Acid react to form and what is observed?

A

Sodium Thiosulfate and Hydrochloric Acid are both clear solutions which react to form a yellow precipitate of sulfur.

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26
Q

What is the experiment between Sodium Thiosulfate and Hydrochloric Acid usually used to investigate?

A

The effect of increasing temperature on reaction rate.

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27
Q

How do you react Sodium Thiosulfate and Hydrochloric Acid?

A
  • Measure out fixed vols of each in measuring cylinders - Use a water bath to heat each to desired temp - Mix solutions in conical flask - Place flask over black cross and time until it isn’t visible
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28
Q

What is a reversible reaction?

A

A reaction that can occur in both directions

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29
Q

What is a dynamic equilibrium?

A

When the forward reaction is happening at the exact same rate as the backward reaction.

30
Q

What is the condition for a dynamic equilibrium?

A

A closed system

31
Q

What is Le Chatalier’s principle?

A

If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of the equilibrium will move to counteract the change.

32
Q

What has to be the same about reactants and products for La Chatalier’s principle to apply and what is this called?

A

They have to be in the same physical state - homogeneous equilibria.

33
Q

What effect does increasing the concentration of a reactant have on the equilibrium?

A

Shifts it to the right

34
Q

What effect does increasing the concentration of a product have on the equilibrium?

A

Shifts it to the left

35
Q

What effect does decreasing the concentration of a reactant have on the equilibrium?

A

Shifts it to the left

36
Q

What effect does decreasing the concentration of a product have on the equilibrium?

A

Shifts it to the right

37
Q

What effect does increasing the pressure of a reaction have on the equilibrium?

A

Shifts to the side with fewer moles

38
Q

What effect does decreasing the pressure of a reaction have on the equilibrium?

A

Shifts it to the side with more moles

39
Q

What effect does increasing the temperature of a reaction have on the equilibrium?

A

Shifts in the endothermic direction

40
Q

What effect does decreasing the temperature of a reaction have on the equilibrium?

A

Shifts it in the exothermic direction

41
Q

What effect does using a catalyst have on the equilibrium?

A

No effect.

42
Q

What is Kc?

A

Equilibrium Constant

43
Q

What is the expression for Kc?

A

aA + bB ⇌ dD eE

Kc = [D]d[E]e/[A]a[B]b

44
Q

How do you calculate units for Kc?

A

Put units into expression and cancel.

45
Q

What condition is Kc dependent on?

A

Temperature

46
Q

If temp change forms more product, how is Kc affected?

A

It increases

47
Q

If temp change forms more reactants, how is Kc affected?

A

It will decrease.

48
Q

If concentration is changed, how is Kc affected?

A

No change

49
Q

If a catalyst is used, how is Kc affected?

A

No change.

50
Q

What happens during oxidation?

A

Loss of electrons

51
Q

What happens during reduction?

A

Gain in electrons

52
Q

What happens in a redox reaction?

A

Oxidation and reduction occur simultaneously.

53
Q

What does an oxidising agent do?

A

Accepts electrons and gets reduced.

54
Q

What does a reducing agent do?

A

Donates electrons and gets oxidised.

55
Q

What does the oxidation state of an element tell you?

A

The total number of electrons it has donated or accepted.

56
Q

What is the oxidation state of elements?

A

0

57
Q

What is the oxidation state of elements bonded to identical atoms? (eg. O2)

A

0

58
Q

What is the oxidation state of a simple monatomic ion?

A

Same as its charge.

59
Q

What is the oxidation state of compound ions?

A

Same as the ion charge

60
Q

What is the oxidation state of a neutral compound?

A

0

61
Q

What is usually the oxidation state of combined oxygen?

A

-2

62
Q

What is the oxidation state of combined oxygen in peroxides?

A

-1

63
Q

What is the oxidation state of combined hydrogen usually?

A

+1

64
Q

What is the oxidation state of combined hydrogen in metal hydrides?

A

-1

65
Q

What do Roman numerals tell you about a chemical?

A

Its oxidation state

66
Q

What do ionic half equations show?

A

Oxidation or Reduction

67
Q
A
68
Q
A
69
Q
A
70
Q
A

A Level Physical Chemistry (9 decks)

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