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Advanced Higher Chemistry > U2-1 - Chemical Equilibrium > Flashcards

U2-1 - Chemical Equilibrium Flashcards

1
Q

What is K?

A

The equilibrium constant

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2
Q

Where do the powers a b c d come from?

A

The balanced equation

(number in front of each species)

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3
Q

What do the square brackets [] mean?

A

Concentration

(in mol l-1)

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4
Q

What are the units of K?

A

It has no units

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5
Q

Write an equilibrium expression for:

2SO2(g) + O2(g) ⇌ 2SO3(g)

A
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6
Q

What does it mean if K > 1?

A

Products are favoured

(High yield of product)

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7
Q

What does it mean if K < 1?

A

Reactants are favoured

(Low yield of product)

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8
Q

The value of K depends only on …

A

temperature.

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9
Q

The concentration of liquids and solids is always …

A

1

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10
Q

Heat is added to an exothermic reaction.

The value of K will …

A

decrease.

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11
Q

Heat is added to an endothermic reaction.

The value of K will …

A

increase.

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12
Q

If a catalyst is added, the value of K…

A

doesn’t change.

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13
Q

Only the initial concentration is given for a reactant.

What must be done before calculating K?

A

Must find the equilibrium concentration.

(initial c – used up c = equilibrium c)

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14
Q

Write the water equilibrium

A

H2O(ℓ) + H2O(ℓ) ⇌ H3O+(aq) + OH−(aq)

OR

H2O(ℓ) ⇌ H+(aq) + OH−(aq)

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15
Q

State the Brønsted-Lowry definition of an acid

A

Proton (H+) donor

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16
Q

State the Brønsted-Lowry definition of a base

A

Proton (H+) acceptor

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17
Q

Amphoteric

A

Can react as both an acid and a base

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18
Q

Write an expression for the ionic product of water

A
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19
Q

How can pH be calculated if we know [OH–]?

A

Calculate pOH = –log[OH–]

Then use pH + pOH = 14

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20
Q

Conjugate base

A

Species formed when an acid loses a proton (H+)

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21
Q

Conjugate acid

A

Species formed when a base gains a proton (H+)

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22
Q

Identify the conjugate acid

HCN(aq) + H2O(ℓ) ⇌ CN−(aq) + H3O+(aq)

A

H3O+(aq)

23
Q

Identify the conjugate base

HCN(aq) + H2O(ℓ) ⇌ CN−(aq) + H3O+(aq)

A

CN−(aq)

24
Q

Strong acid/base

A

Completely dissociates into ions in aqueous solution

25
Q

Weak acid/base

A

Only partially dissociates into ions in aqueous solution

26
Q

Examples of strong acids

A

HCl

H2SO4

HNO3

27
Q

Examples of strong bases

A

Metal hydroxides

28
Q

Examples of weak acids

A

CH3COOH (any organic acid)

H2CO3 (carbonic acid)

H2SO3 (sulfurous acid).

29
Q

Examples of weak bases

A

NH3

amines (contain -NH2 group)

30
Q

What is Ka?

A

Acid dissociation constant

31
Q

If Ka is low, the acid is …

A

Weak

(only partially dissociates)

32
Q

If Ka is high, the acid is …

A

Strong

(fully dissociates)

33
Q

For strong acids, pKa is …

A

low.

34
Q

For weak acids, pKa is …

A

high.

35
Q

Which will conduct electricity better:

a strong or weak acid solution?

A

Strong

(More ions in solution at same concentration)

36
Q

Which will have lower pH at the same concentration:

strong or weak acid?

A

Strong

(more H+ ions in solution)

37
Q

A salt of a strong acid and strong base will have pH …

A

7 (neutral).

38
Q

A salt of a strong acid and weak base will have pH …

A

<7 (acidic).

39
Q

A salt of a weak acid and strong base will have pH …

A

>7 (alkaline).

40
Q

Explain why the salt of a weak acid and strong base is alkaline.

A

Conjugate base of weak acid removes H+ from solution.

Water equilibrium shifts to the right, making excess OH– ions.

41
Q

Explain why the salt of a strong acid and weak base is acidic.

A

Conjugate acid (NH4+) removes OH– from solution.

Water equilibrium shifts to the right, making excess H+ ions.

42
Q

When can we see an obvious colour change between HIn and In–?

A

When [HIn] and [In–] differ by a factor of 10.

43
Q

Equivalence point

A

The exact point of neutralisation

(solution pH is the same as the pH of the salt formed)

44
Q

How do you know if an indicator is suitable for a titration?

A

Colour must change around the equivalence point

45
Q

Why can’t indicators be used for weak acid/weak base titrations?

A

pH change too gradual around equivalence point

(hard to see indicator colour change)

46
Q

Buffer solution

A

A solution in which the pH remains approximately constant when small volumes of acid, base or water are added.

47
Q

An acid buffer consists of …

A

a weak acid and one of its salts made from a strong base.

48
Q

A basic buffer consists of …

A

a weak base and one of its salts.

49
Q

Adding a small volume of water does not change buffer pH.

Why?

A

The acid and salt will be diluted by equal amounts.

(acid/salt ratio is unchanged)

50
Q

Sodium hydroxide is added to an acid buffer.

How does it resist change in pH?

A

H+ + OH– → H2O (removes H+ from solution)

acid equilibrium shifts to the right (HA ⇌ H+ + A–)

51
Q

Sodium hydroxide is added to a basic buffer.

How does it resist change in pH?

A

H+ + OH– → H2O (removes OH–)

Conjugate acid NH4+ supplies H+ ions to replace ones removed

52
Q

Hydrochloric acid is added to a basic buffer.

How does it resist change in pH?

A

H+ + OH– → H2O (weak base removes H+)

Base equilibrium shifts to the right to replace OH–

53
Q

Hydrochloric acid is added to an acid buffer.

How does it resist change in pH?

A

Conjugate base (from the salt) absorbs H+ to form weak acid

Advanced Higher Chemistry (15 decks)

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