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2016 GAMSAT > Chemistry - Equilibria, Energetics and Elements - F325 - Rates, Equilibrium and pH (1) > Flashcards

Chemistry - Equilibria, Energetics and Elements - F325 - Rates, Equilibrium and pH (1) Flashcards

1
Q

Define the rate of reaction.

A

The rate of reaction is the change in concentration of a reactant or product per unit time.

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2
Q

Collisions must have more energy than what for a reaction to take place?

A

Collisions must have more energy that the activation energy for a reaction to take place.

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3
Q

How can the proportion of molecules that exceed the activation energy be altered?

A

The proportion of molecules that exceed the activation energy can be altered by changing the temperature or by adding a catalyst.

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4
Q

What is the equation for the rate?

A

Rate = (change in concentration of a reactant or product) / (time taken for the change to take place) moldm-3s-1

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5
Q

Rate is plotted on a graph of what against what?

A

Rate is plotted on a graph of time against concentration.

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6
Q

To measure reaction rates involving acids or bases what can you measure?

A

Measure pH change usinf a pH meter or by titration.

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7
Q

To measure reaction rates involving the production of gases, what can be measured?

A

Measure the change in volume or pressure or loss in mass of reactants.

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8
Q

To measure reaction rates that produce visual changes, what can be measured?

A

Can observe the formation of a precipitate or a colour change.

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9
Q

If the order is 0 with respect to reactant A, then how does changing the concentration of A affect the rate?

A

If the order is 0 with respect to reactant A then the rate is unaffected by changing the concentration of A.

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10
Q

If the order is 1 with respect to reactant A, then how does changing the concentration of A affect the rate?

A

If the order is 1 with respect to reactant A then if A increases 2 times the rate will also increase by 2 times.

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11
Q

If the order is 2 with respect to reactant A, then how does changing the concentration of A affect the rate?

A

If the order is 2 with respect to reactant A then if A increases by 2 times, the rate will increase by 4 times.

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12
Q

What would be the rate equation for the reaction A + B –> C ?

A

The rate equation would be:
rate = [A]^m[B]^n
where m is the order of reaction with respect to A
n is the order of reaction with respect to B

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13
Q

What is the overall order of reaction?

A

The overall order of reaction is the sum of the individual orders.

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14
Q

What does the rate constant, k, link the rate of reaction with?

A

The rate constant, k, is the constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation.

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15
Q

What is the half life of a reactant?

A

The half life of a reactant is the time taken for the concentration of the reactant to reduce by half.

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16
Q

What is the half life of a first order reaction?

A

A first order reaction has a constant half life. The half life is the same no matter what the concentration is.

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17
Q

What is the half life of a zero order reaction?

A

A zero order reaction, the concentration decreases at a constant rate, the half life decreases with time.

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18
Q

What is the half life of a second order reaction?

A

For second order reactions, the concentration decreases rapidly but the rate of decrease then slows down. The half life increases with time.

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19
Q

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

A

Flat horizontal line.

The rate is unaffected by changes in concentration.

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20
Q

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

A

Linear relationship.

If the concentration of A doubles, then so does the rate.

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21
Q

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

A

Quadratic relationship.

If A increases by 2 times then the rate increases by 4 times.

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22
Q

How is the initial rate calculated?

A

To calculate the initial rate, draw a tangent from t=0 or a clock reaction.

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23
Q

A fast reaction will have a …….. value of k.

A

A fast reaction will have a large value of k.

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24
Q

A slow reaction will have a ………….. value of k.

A

A slow reaction will have a small value of k.

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25
Q

What is the rate-determining step?

A

The rate-determining step is the slowest step in the reaction mechanism of a multi-step reaction.

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26
Q

How do you know a reactant is involved in the rate determining step?

A

If a reactant appears in the rate equation, the reactant is involved in the rate-determining step.

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27
Q

What is a dynamic equilibrium?

A

A dynamic equilibrium is established in a closed system when the rate of the forward reaction is the same as the rate of the reverse reaction and the concentrations of the reactants and products remains the same.

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28
Q

What is Kc?

A

Kc is the equilibrium constant in terms of concentrations.

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29
Q

The equilibrium law states that for the equation aA + bB cC + dD, Kc = ?

A

Kc = [C]^c[D]^d / [A]^a[B]^b

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30
Q

Define a homogeneous equilibrium.

A

A homogeneous equilibrium is an equilibrium in which all the species making up the reactants and products are in the same physical state.

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31
Q

Define a heterogeneous equilibrium.

A

A heterogeneous equilibrium is an equilibrium in which species making up the reactants and products are in different physical states.

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32
Q

The magnitude of Kc indicates what?

A

The magnitude of Kc indicates the extent of a chemical reaction.

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33
Q

What does a Kc value of 1 indicate?

A

A Kc value of 1 indicates that the position of equilibrium is halfway between the reactants and the products.

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34
Q

What does a Kc value greater than 1 indicate?

A

A Kc value greater than 1 indicates that the reaction is product favoured.

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35
Q

What does a Kc value less than 1 indicate?

A

A Kc value less than 1 indicates that the reaction is reactant favoured.

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36
Q

What makes Kc shift position?

A

Kc shifts position only with changes in temperature.

37
Q

When the forward reaction is endothermic as temperature increases, what happens to Kc?

A

When the forward reaction is endothermic, as temperature increases Kc increases.

38
Q

When the forwards reaction is exothermic, as temperature increases what happens to Kc?

A

When the forwards reaction is exothermic, as temperature increases, Kc decreases.

39
Q

What happens to Kc with changes in concentration?

A

Kc is unaffected by changes in concentration.

40
Q

What happens to Kc with changes in pressure?

A

Kc is unaffected by changes in pressure.

41
Q

At low temperatures, are Kc and k big or small?

A

At low temperatures Kc is large (reverse reaction is endothermic) but k is small (low temperature).

42
Q

At high temperatures, are Kc and k big or small?

A

At high temperatures, Kc is small (forward reaction is exothermic) but k is large (high temperature).

43
Q

Define an Arrhenius acid.

A

An Arrhenius acid dissociates when dissolved in water to form hydrogen ions, H+.

44
Q

Define an Arrhenius base.

A

An Arrhenius base dissociates when dissolved in water to for, hydroxide ions, OH-.

45
Q

Define a Bronsted-Lowry acid.

A

A Bronsted-Lowry acid is any substance from which a proton can be removed.

46
Q

Define a Bronsted-Lowry base.

A

A Bronsted-Lowry base is any substance that can remove a proton from an acid.

47
Q

Define a Lewis acid.

A

A Lewis acid is an electron pair acceptor.

48
Q

Define a Lewis base.

A

A Lewis base is an electron pair donor.

49
Q

What is a monobasic acid?

A

A monobasic acid is one that can release one proton.

50
Q

Give an example of a monobasic acid.

A

HCl is a monobasic acid.

51
Q

What is a dibasic acid?

A

A dibasic acid is one that can release two protons.

52
Q

Give an example of a dibasic acid.

A

H2SO4 is a dibasic acid.

53
Q

What is a tribasic acid?

A

A tribasic acid is one that can release three protons.

54
Q

Give an example of a tribasic acid.

A

H3PO4 is a tribasic acid.

55
Q

Define a neutralisation reaction.

A

Neutralisation is a chemical reaction in which an acid and a base react together to produce a salt and water.

56
Q

When water molecules accept a proton, what is formed?

A

When water molecules accept a proton, a hydronium (or oxonium) ion H3O+(aq) is formed.

57
Q

What is an acid-base pair?

A

An acid-base pair is a pair of two species that transform into each other by gain or loss of a proton.

58
Q

Who developed the pH scale?

A

Soren Sorenson developed the pH scale.

59
Q

In what year was the pH scale devised?

A

The pH scale was developed in 1909 by Soren Sorenson.

60
Q

pH= ?

A

pH=-log[H+(aq)]

61
Q

[H+(aq)] = ?

A

[H+(aq)] = 10^-pH

62
Q

Why is the relationship between pH and [H+(aq)] sometimes called a ‘see-saw’ relationship?

A

The relationship between pH and [H+(aq)] is sometimes called a see-saw relationship because when one is up, the other is down.

63
Q

The strength of an acid, HA, is what….?

A

The strength of an acid, HA, is the extent of its dissociation into H+ and A- ions.

64
Q

The extent of acid dissociation is measured by what?

A

The extent of acid dissociation is measured by an equilibrium constant called the acid dissociation constant, Ka.

65
Q

How is the acid dissociation constant, Ka, of an acid, HA defined?

A

The acid dissociation constant Ka of an acid HA is defined as:
Ka = [H+(aq)][A-(aq)]/[HA(aq)]

66
Q

What are the units of Ka?

A

The units of Ka are always moldm-3.

67
Q

What does a large value of Ka indicate?

A

A large value of Ka indicates a large extent of dissociation - the acid is strong.

68
Q

What does a small value of Ka indicate?

A

A small Ka value indicates a small extent of dissociation - the acid is weak.

69
Q

pKa = ?

A

pKa = -log10Ka

70
Q

Ka = ?

A

Ka = 10^pKa

71
Q

Because strong acids virtually completely dissociate in water [H+(aq)] of a strong acid is equal to what?

A

Because strong acids virtually dissociate in water [H+(aq)] of s trong acid is equal to the concentration of the acid.

72
Q

What represents the ionic product of water?

A

Kw is the ionic product of water.

73
Q

The ionic product of water, Kw, is defined as Kw= ?

A

Kw=[H+(aq)][OH-(aq)]

74
Q

At 25oC what does Kw = ?

A

At 25oC Kw = 1.00 x 10^-14 mol2dm-6

75
Q

What is a buffer solution?

A

A buffer solution is a mixture that minimises pH changes on addition of small amounts of acid or base.

76
Q

What is a buffer solution made of?

A

A buffer solution is made of a weak acid HA and its conjugate base A-.

77
Q

If the pH of human blood plasma falls below 7.35 what occurs?

A

If the pH of human blood plasma falls below 7.35 then a condition called acidosis occurs.

78
Q

What is acidosis?

A

Acidosis occurs when the pH of human blood plasma falls below 7.35.

79
Q

If the pH of human blood plasma rises above 7.45 what occurs?

A

If the pH of human blood plasma rises above 7.45 then alkalosis occurs.

80
Q

What is alkalosis?

A

Alkalosis occurs when the pH of human blood plasma rises above 7.45.

81
Q

What is the most important buffer system in the blood?

A

The carbonic acid - hydrogencarbonate ion buffer is the most important buffer system in the blood.

82
Q

Define the equivalence point.

A

The equivalence point s the point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution.

83
Q

Define the end point of a titration.

A

The end point is the point at which there are equal concentrations of the weak acid and conjugate base forms of the indicator.

84
Q

What would be a suitable indicator for a strong acid - strong base reaction?

A

Phenolphthalein or methyl orange would be suitable indicators.

85
Q

What would be a suitable indicator for a strong acid weak base reaction?

A

Phenolphthalein would be an unsuitable indicator, but methyl orange would be a suitable indicator.

86
Q

What would be a suitable indicator for a weak acid - strong base reaction?

A

Phenolphthalein would be a suitable indicator, but methyl orange would be an unsuitable indicator.

87
Q

What would be a suitable indicator for a weak acid- weak base reaction?

A

In a weak acid - weak base reaction the change in pH is a lot more gradual and there is no vertical section which means there are no indicators which are really suitable.

88
Q

Define the standard enthalpy change of neutralisation.

A

The standard enthalpy change of neutralisation, ΔHneut, is the energy change that accompanies the neutralisation of an aqueous acid by an aqueous base to form one mole of H2O(l) under standard conditions.

2016 GAMSAT (19 decks)

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