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AH Chemistry > 2a- Chemical equilibrium > Flashcards

2a- Chemical equilibrium Flashcards

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1
Q

A chemical reaction is said to be in equilibrium when…?

A

The composition of the reactants and products remains constant indefinitely

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2
Q

What does the equilibrium constant (K) characterise?

A

The equilibrium composition of the reaction mixture

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3
Q

What does the value of an equilibrium constant indicate?

A

The position of equilibrium

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4
Q

What units do equilibrium constants have?

A

They have no units

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5
Q

How can the concentrations of pure solids and pure liquids at equilibrium be taken?

A

As constant and given a value of 1 in the equilibrium expression

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6
Q

What does the numerical value of the equilibrium constant depend on?

A

The reaction temperature (concentration and pressure have no effect)

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7
Q

In an exothermic reaction an increase in temperature causes what to happen to the K value and the yield of product?

A

In an exothermic reaction an increase in temperature causes an increase of the K value and an increase in the yield of product

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8
Q

In an endothermic reaction an increase in temperature causes what to happen to the K value and the yield of product?

A

In an endothermic reaction an increase in temperature causes a decrease in the K value and a decrease in the yield of product

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9
Q

What affect does the presence of a catalyst have on the value of the equilibrium constant?

A

A catalyst has no affect

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10
Q

Water is said to be amphoteric, what does this mean?

A

It can react as both an acid and a base

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11
Q

What does the value of the ionic product of water vary with?

A

Temperature

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12
Q

At 25*c what is the approximate value of Kw?

A

1 x 10^-14

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13
Q

In water and aqueous solutions with a pH value of 7, what are the concentrations of both hydronium and hydroxide ions at 25*c?

A

Concentrations of H3O+ and OH- are both 10^-7 mol/l

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14
Q

What do the Bronsted-Lowry definitions of acids and bases state?

A

An acid is a proton donor and a base is a proton acceptor

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15
Q

For every acid there is a…?

A

Conjugate base which is formed by the loss of a proton

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16
Q

For every base there is a…?

A

Conjugate acid which is formed by the gain of a proton

17
Q

What is a characteristic of strong acids and bases?

A

Strong acids and bases completely dissociate into ions in aqueous solution

18
Q

What is a characteristic of weak acids and bases?

A

Weak acids and bases only partially dissociate into their ions in aqueous solution

19
Q

What are three examples of strong acids?

A
  • hydrochloric acid (HCl)
  • sulfuric acid (H2SO4)
  • nitric acid (HNO3)
20
Q

What are three examples of weak acids?

A
  • carboxylic acids (e.g. ethanoic acid)
  • carbonic acid (H2CO3)
  • sulfurous acid(H2SO3)
21
Q

What is an example of a strong base?

A
  • solutions of metal hydroxides (except Mg)
22
Q

What are two examples of weak bases?

A
  • ammonia (NH3)

- amines

23
Q

What is the relationship between the Ka value and the strength of the acid?

A

The smaller the Ka value, the weaker the acid is

24
Q

A soluble salt of a strong acid and a strong base dissolves in water to produce what?

A

A neutral solution

25
Q

A soluble salt of a strong acid and a weak base dissolves in water to produce what?

A

An acidic solution

26
Q

A soluble salt of a weak acid and a strong base dissolves in water to produce what?

A

An alkaline solution

27
Q

What does the name of a salt depend on?

A

The acid and base used

28
Q

What is a buffer solution?

A

One in which the pH remains approximately constant when small amounts of acid, base or water are added

29
Q

What is an acidic buffer made with?

A

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

30
Q

What is a basic buffer solution made with?

A

A weak base and one of its salts

31
Q

What are indicators?

A

Weak acids which change colour depending on the pH of the solution

32
Q

How is the colour of the indicator determined?

A

By the ratio of the concentrations of HIn ions to In- ions

33
Q

The colour change is for an indicator is assumed to be distinguishable at what point?

A

When the concentrations of HIn ions and In- ions differ by a factor of 10

34
Q

How can suitable indicators be selected?

A

From pH data, including titration curves

AH Chemistry (15 decks)

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