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OCR Chemistry > 5.1 RATES,EQUILIBRIUM & PH > Flashcards

5.1 RATES,EQUILIBRIUM & PH Flashcards

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1
Q

Define rate of reaction

A
  • Change in concentration of a reactant or product per unit time
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2
Q

Define order

A
  • The power to which the concentration of a reactant is raised to in the rate equation
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3
Q

What does rate constant, K link?

A
  • Links rate of reaction with concentration of reactions raised to their orders
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4
Q

State the rate equation

A
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5
Q

Define overall order

A
  • The sum of the individual orders in the rate equation
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6
Q

Define half life (of a reactant)

A
  • the time taken for the concentration of a reactant to reduce by half
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7
Q

Define rate-determining step

A
  • the slowest step of a multi-step reaction that determines the rate at which the overall reaction proceeds
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8
Q

What is meant by a reactant in zero order?

A
  • The rate is unaffected by changing concentration of that reactant
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9
Q

What is meant by a reactant in first order?

A
  • The rate is directly proportional to the concentration of that reactant
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10
Q

What is meant by a reactant in second order?

A
  • The rate is equal to the change in concentration squared of that reactant
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11
Q

State which reactant order does NOT appear in the rate equation

A
  • Zero order reactants
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12
Q

Draw all the orders on a concentration-time graph

A
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13
Q

Draw all the orders on a rate-concentration graph

A
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14
Q

State how the rate of reaction would be determined from a concentration-time graph that produces a curved line of best fit

A
  • A tangent to the curve at given point
  • Find the gradient using Δconc/time taken (=Δy/Δx)
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15
Q

Define half-life

A
  • The time taken for the concentration of a reactant to reduce by half
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16
Q

State and explain which type of rate graph we identify the half life for

A
  • Concentration-time graphs of FIRST ORDER reactants
  • Because the half life is independant of concentrations so each half life is the same length
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17
Q

State the equation that links half-life with rate constant K

A
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18
Q

State how to work out initial rate from a concentration-time graph

A
  • Draw a tangent at t=0 and work out the gradient (Δy/Δx)
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19
Q

State the relationship between reactants in the rate-determining step and the reactants in the rate equation

A
  • Only and all of the reactants that appear in the rate equation must be in the rate-determining (slow) step

(im unsure if this is right, look at ur notes, hivi)

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20
Q

State the arrhenius equation

A
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21
Q

State what the arrhenius equation links

A
  • Links activation energy and temperature to the rate constant K
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22
Q

State the reason for use of a colourimeter

A
  • Monitors visual colour changes
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23
Q

Define continuos monitoring

A
  • Taking measurements of rates at specific intervals to measure the change in quantity of a substance
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24
Q

Explain the effect of temperature of the rate constant and hence, the rate of reaction

A
  • As temperature increases, more KE given to particles
  • Thus, more frequent successful collisions with sufficient energy to exceed activation energy
  • This increases the value of the rate constant and therefore also the rate of reaction
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25
Q

State how we get rid of the exponential eˣ in the arrhenius equation

A
  • We natural log (ln) BOTH sides of the equation
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26
Q

State which two parts of the arrhenius equation we can be asked to determine graphically AND state the new rearranged arrhenius equation we would use

A

1) Activation energy Ea
2) Arrhenius constant A

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27
Q

State the arrhenius equation after it has been natural logged (ln)

A
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28
Q

Define homogenous equilibrium

A
  • Equilibrium where all species making up reactants and products are in the same physical state
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29
Q

Define heterogenous equilibrium

A
  • Equilibrium where the species making up reactants and products are in the different physical states
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30
Q

State what we do if we need to determine a Kₚ or Kc expression for a heterogenous equilibrium

A
  • NEVER include solid and liquid species
  • (Only gaseous and aqueous)
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31
Q

State what the ICE table stands for and which questions we use it in

A

Initial moles, Change in moles, Equilibrium moles
- Use in any type of equilibrium questions

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32
Q

State the Kc expression

A
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33
Q

Define partial pressure

A
  • The pressure an individual gaseous substance would exert if it occupied the whole reaction vessel alone
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34
Q

Define total pressure

A
  • The sum of all individual pressures (partial pressures)
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35
Q

Define mole fraction

A
  • The proportion of a given substance present in a reaction mixture
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36
Q

State the formula for partial pressure

A
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37
Q

State the formula for total pressure

A
38
Q

State the formula for mole fractions

A
39
Q

State the Kₚ expression

A
40
Q

State what a value of 1 for Kc or Kp would indicate

A
  • That equilibrium lies in the middle
41
Q

State what a value greater than 1 for Kc or Kp would indicate

A
  • That equilibrium lies toward the right/products/forward
42
Q

State what a value less than 1 for Kc or Kp would indicate

A
  • That equilibrium lies toward the left/reactants/backward
43
Q

Define a bronsted-lowry acid

A
  • A proton donor species
44
Q

Define a bronsted-lowry base

A
  • A proton acceptor species
45
Q

Define monobasic, dibasic and tribasic acids

A
  • Monobasic acid means each molecule releases one proton (e.g HCl)
  • Dibasic acid means each molecule releases two protons (e.g H₂SO₄)
  • Tribasic acid means each molecule releases three protons (e.g H₃PO₄)
46
Q

Define conjugate acid-base pair

A
  • A set of two species that turn into each other by the gain or loss of a proton
47
Q

What does the acid dissociation constant, Ka measure?

A
  • The actual extent of acid dissociation
48
Q

State the Kₐ expression then simplify it.

A
49
Q

State the two expressions that convert between Kₐ and pKₐ

A
50
Q

State what a large Kₐ value indicates

A
  • A large Kₐ value means a large extent of acid dissociation
  • The acid is strong
51
Q

State what a small Kₐ value indicates

A
  • A small Kₐ value means a small extent of acid dissociation
  • The acid is weak
52
Q

State what a high/low pKₐ value indicates

A
  • High pKₐ means a weaker acid
  • Low pKₐ means a stronger acid
53
Q

State the two expressions that convert between pH and [H⁺]

A
54
Q

State what a pH change of 1 would increase [H⁺] by

A
  • A pH change of 1 increases the [H⁺] by 10 times
55
Q

Define strong acid and draw an equation

A
  • An acid that fully dissociates in aqueous solution to release H+ ions
56
Q

Define weak acid and draw an equation

A
  • An acid that partially dissociates in aqueous solution to release H+ ions
57
Q

State the assumption made for strong monobasic acids

A

We assume:
[H⁺] = [HA]

58
Q

State the two assumptions made for weak monobasic acids

A

We assume:
1) [H⁺] = [A⁻]
2) [HA] undissaociated = [HA] equilibrium

59
Q

State the Ka expression for a strong monobasic acid

A
60
Q

State the Ka expression for a weak monobasic acid

A
61
Q

State the equation to find [H⁺] of a weak acid

A
62
Q

Explain the limitation of assumption used for weak acids

A
  • We assume that:
    [HA] undissaociated = [HA] equilibrium
  • However for “stronger” weak acids that dissociate more than 5% we cannot use the assumption above
  • This is because “stronger” weak acids would have a higher Ka value than we calcuated, we are underassuming
63
Q

State the reaction for ionisation of water and state where equilibrium lies

A
  • Equilibrium lies well to the left
64
Q

State what the ionic product of water Kᵥᵥ expression determines

A
  • The relative concentrations of H+ and OH- of an aqueous solution
65
Q

State the Kᵥᵥ expression

A
66
Q

State the assumption made for pure water

A

We assume:
[H⁺]=[OH⁻]

67
Q

Define alkali

A
  • A water soluble base that dissociates to release OH- ions in solution
68
Q

State three strong alkalis

A

1) NaOH
2) KOH
3) Ca(OH)₂

69
Q

State a weak alkali

A

NH₃

70
Q

State the assumption we make for strong monobasic alkalis

A

We assume:
[OH⁻]=[NaOH]

71
Q

State the equation to find [H⁺] of a strong monobasic alkali

A
72
Q

Define buffer solution

A
  • A mixture that minimised pH changes on small additions of acids or bases
73
Q

State what a buffer solution is made of

A
  • A weak acid, HA
  • Its conjugate base, A⁻
74
Q

State the three ways of making a buffer solution

A

1) A solution of weak acid + a solution of its salt
2) A solution of weak acid + its solid salt
3) An EXCESS solution of weak acid + an alkali (partial neutralisation)

75
Q

State the reaction for a buffer mixture and state their relative proportions

A
76
Q

Describe the dissociation of salts thus, state the assumption we make

A
  • Salts fully dissociate into its cations and its anions when in water
    We assume:
    [Salt]=[A⁻]
77
Q

State the equation to determine the [H⁺] of a buffer solution

A
78
Q

Explain the effect of adding acid to a buffer solution

A

(CONJUGATE BASE REMOVES ADDED H⁺)
- [H⁺] increases
- The conjugate base A⁻ reacts with the added H⁺ ions, to form more acid HA
- Equilibrium shifts to the left, removing the added H⁺ ions

79
Q

Explain the effect of adding alkali to a buffer solution

A

(CONJUGATE BASE REMOVES ADDED H⁺)
- [OH⁻] increases
- The small concentration of H⁺ reacts with the added OH⁻ ions, to form more water molecules
- HA dissociates to restore the lost H⁺
- Equilibrium shifts to the right, removing the added OH⁻ ions

80
Q

Explain the role of the carbonic acid-hydrogen carbonate buffer solution

A
  • Healthy blood pasma is 7.35 to 7.45
  • carbonic acid-hydrogen carbonate buffer solution controlls blood pH
  • hydrogencarbonate ions can remove acidic stuff released into the blood by converting into carbonic acid
  • Enzymes then convert this to aqueous carbon dioxide then into gasesous carbon dioxide which is then exhaled in the lungs
81
Q

Define equivalence point

A
  • The point where the volume of one solution has reacted exactly with the volume of the second solution
82
Q

Explain how to calibrate a pH probe

A
  • Rinse the probe in deionised water
  • Blott dry and place into solution of known pH
  • Leave it to read and ensure it reads the correct pH
  • Repeat with pH 4/7/10
83
Q

State what an indicator is and how it works

A
  • An indicator is just a weak acid (HIn)
  • It has one colour as a weak acid and another colour as a conjugate base
84
Q

Define endpoint

A
  • When there are equal concentrations of weak acid and conjugate base
  • The colour of the endpoint is midway of the indicators two colours
    [HIn] = [In⁻]
85
Q

State how to pick a suitible indicator

A
  • the end point of the indicator needs to have a pH value as close as possible to the equivilence point pH value of the titration
86
Q

Draw out the four types of titration curves

A
87
Q

Explain why no indicator is suitible for a weak acid-weak base titration

A
  • Because there literally is no equivalence point
88
Q

Do catalysts increase concentrations of reactants/products

A
  • NO catalysts have no effect on equilibrium concentration
  • (They only increase rate of attainment of equilibrium)
89
Q

Do catalysts increase the Kc value

A
  • NO catalysts have no effect on equilibrium concentrations
  • (They only increase rate of attainment of equilibrium)
90
Q

State the formula to determine pre-exponential factor A from lnA

A

OCR Chemistry (13 decks)

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