Chemical equillibrium

Question 1

A chemical reaction is in equilibrium when?

Answer 1

The composition of the reactants and products remains constant indefinitely.

Question 2

What does the equillibrium constant (K) characterise?

Answer 2

The equilibrium composition of the reaction mixture.

Question 3

The concentrations of pure solids and liquids at equillibrium are taken as constant and given a value of — in the equillibrium expression.

Answer 3

1

Question 4

If K»1 The equillibrium position is?

Answer 4

Right

Question 5

If K~1 The equillibrium position is?

Answer 5

Neither right nor left

Question 6

If K«1 The equillibrium position is?

Answer 6

Left

Question 7

If the value of K is <10*^-3, what will the extent of the reaction be?

Answer 7

Effectively no reaction.

Question 8

If the value of K is 10^-3 to 10^3, what will the extent of the reaction be?

Answer 8

Significant quantities of both reactants and products at equillibrium.

Question 9

If the value of K is > 10*^-3, what will the extent of the reaction be?

Answer 9

Reaction is effectively complete

Question 10

For an endothermic reaction a rise in temperature causes an?

Answer 10

Increase in K and the yield of product is increased.

Question 11

For an exothermic reaction a rise in temperature causes an?

Answer 11

Decrease in K and the yield of product is decreased.

Question 12

Does the prescence of a catalyst affect the value of K?

Answer 12

No

Question 13

What is H30+?

Answer 13

It represents a hydronium ion, a hydrated proton. A shorthand representation of H30+ is H+.

Question 14

Water is amphoteric, what does this mean?

Answer 14

Can react as an acid and a base.

Question 15

In water and aqueous solutions with a pH of 7 the concentration of H30+ and OH- are both?

Answer 15

10*^-7 mol L-1at 25°C

Question 16

Brønstead-Lowry definition of a base?

Answer 16

Proton acceptor

Question 17

Brønstead-Lowry definition of an acid?

Answer 17

Proton donor.

Question 18

Every acid has a conjugate base formed by?

Answer 18

The loss of a proton.

Question 19

Every base has a conjugate acid formed by?

Answer 19

The gain of a proton.

Question 20

Strong acids and bases?

Answer 20

Completely dissociated into ions in aqueous solutions.

Question 21

Weak acids and bases?

Answer 21

Only partially dissociated into ions in aqueous solutions.

Question 22

Examples of weak acids?

Answer 22

Ethanoic acid, carbonic acid and sulfurous acid.

Question 23

Examples of strong acids?

Answer 23

HCl, sulfuric acid and nitric acid.

Question 24

Examples of strong bases?

Answer 24

Solutions of metal hydroxides.

Question 25

Examples of weak bases?

Answer 25

Ammonia or amines.

Question 26

For the same concentration of acid the strong acid:

Answer 26

- has higher concentration of H+ ions so lower pH. - has higher concentration of ions so higher conductivity and reacts faster.

Question 27

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

Answer 27

Neutral solution.

Question 28

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

Answer 28

Alkaline solution.

Question 29

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

Answer 29

Acidic solution.

Question 30

What is a buffer solution?

Answer 30

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

Question 31

What does an acid buffer consist of?

Answer 31

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

Question 32

How does an acid buffer solution work?

Answer 32

Weak acid provides H+ ions when these are removed by the addition of a small amount of base. Salt of the weak acid provides the conjugate base, which can absorb excess H+ ions produced by the addition of a small amount of acid.

Question 33

What does a basic buffer consist of?

Answer 33

A solution of a weak base and one of its salts.

Question 34

How does a basic buffer work?

Answer 34

The weak base removes the excess H+ ions The conjugate acid provided by the salt supplies H+ ions when these are removed.

Question 35

What are indicators?

Answer 35

Weak acids.

Question 36

In aqueous solution the colour of an acid indicator is —— —— from that of its conjugate base.

Answer 36

Distinctly different.

Question 37

The colour of the indicator is determined by the ratio of?

Answer 37

[HIn] to [In-]

Question 38

The theoretical point at which the colour change occurs is when?

Answer 38

[H30+] = Kin

Question 39

The colour change is assumed to be distinguishable when?

Answer 39

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