2.1 chemical equilibrium

Question 1

when is a chemical reaction in equilibrium

Answer 1

when the composition of the reactants and products remains constant indefinitely

Question 2

what is K

Answer 2

the equilibrium constant

Question 3

what does the equilibrium constant do

Answer 3

characterises the equilibrium composition of the reaction mixture

Question 4

what are A, B, C, D in the equilibrium expression

Answer 4

the equilibrium concentrations

Question 5

what are a,b,c,d in the equilibrium expression

Answer 5

the stoichiometric coefficients

Question 6

can the value of K be calculated

Answer 6

yes

Question 7

what does the value of K indicate

Answer 7

the position of the equilibrium

Question 8

what are the units for K

Answer 8

there aren’t units for K

Question 9

what are the concentrations of pure solids and pure liquids at equilibrium taken as

Answer 9

constant

Question 10

what value are the concentrations of pure solids and liquids at equilibrium given in the equilibrium expression

Answer 10

1

Question 11

what does the numerical value of K depend on

Answer 11

the reaction temperature

Question 12

can K be altered by concentration and/or pressure

Answer 12

no

Question 13

what happens to the value of K if the temperature is increased during an endothermic reaction

Answer 13

increase

Question 14

what happens to the value of K if the temperature is decreased in an endothermic reaction

Answer 14

decrease

Question 15

what happens to the value of K if the temperature is increased during an exothermic reaction

Answer 15

decrease

Question 16

what happens to the value of K if the temperature is decreased in an exothermic reaction

Answer 16

increase

Question 17

does the presence of a catalyst affect the value of the equilibrium constant

Answer 17

no

Question 18

what is there an equilibrium between - in water and aq solutions

Answer 18

there is one between the water molecules and hydronium and hydroxide ions

Question 19

what is the equation for the ionisation of water

Answer 19

H2O + H2O -> H3O+ + OH-

Question 20

what is the chemical formula for a hydronium ion

Answer 20

H3O+

Question 21

what is a hydronium ion

Answer 21

a hydrated proton

Question 22

what does amphoteric mean

Answer 22

it can react as an acid and a base

Question 23

is water amphoteric? why can you conclude this?

Answer 23

yes, because it can react as an acid or as a base

Question 24

what is the dissociation constant for the ionisation of water known as? what is it represented by?

Answer 24

it is known as the ionic product and it is represented by Kw

Question 25

does the value of ionic product vary with temperature

Answer 25

yes

Question 26

what is the value of Kw at 25 degrees (approx)

Answer 26

1x10-14

Question 27

what is the Bronsted Lowry definition of acids and bases

Answer 27

an acid is a proton donor, and a base is proton acceptor

Question 28

what is formed by the loss of a proton, for every acid?

Answer 28

a conjugate base

Question 29

what is formed by the gain of a proton, for every base?

Answer 29

a conjugate acid

Question 30

which type of acids and bases are completely dissociated into ions in aqueous solution

Answer 30

strong

Question 31

which type of acids and bases are only partially dissociated into ions in aqueous solutions

Answer 31

weak

Question 32

what are some examples of strong acids

Answer 32

- hydrochloric acid - sulfuric acid - nitric acid

Question 33

what are examples of weak acids

Answer 33

- ethanoic acid - carbonic acid - sulfurous acid

Question 34

what is an example of a strong base

Answer 34

solutions of metal hydroxides (eg sodium hydroxide)

Question 35

what are examples of weak bases

Answer 35

ammonia and amines

Question 36

how can the weakly acidic nature of some substances be explained

Answer 36

reference to the equations showing the equilibria

Question 37

what are the differences between the equimolar solutions of weak and strong acids

Answer 37

- pH values - conductivity - reaction rates

Question 38

what are the similarities between equimolar solutions of weak and strong acids

Answer 38

the stoichiometry of reactions are the same

Question 39

what two acids and bases dissolve in water to produce neutral solutions

Answer 39

- strong acid and strong base - weak acid and weak base

Question 40

which acid and base dissolve in water to produce an alkaline solution

Answer 40

- weak acid and strong base

Question 41

which acid and base dissolve in water to produce an acidic solution

Answer 41

strong acid and weak base

Question 42

what does the name of the salt produced depend on

Answer 42

the acid and base used

Question 43

what is a buffer solution

Answer 43

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

Question 44

what does an acid buffer consist of

Answer 44

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

Question 45

what occurs in an acid buffer when a small amount of base is added

Answer 45

the weak acid provides hydrogen ions when these are removed by the addition of a small amount of base

Question 46

what occurs in a basic buffer when an acid is added

Answer 46

the weak base removes excess hydrogen ions

Question 47

how can an approx pH of an acid buffer solution be calculated

Answer 47

from its composition and from the acid dissociation constant

Question 48

what are indicators

Answer 48

weak acids

Question 49

what does Kin represent

Answer 49

the acid indicator dissociation

Question 50

when in the colour of an acid indicator distinctly different from that of its conjugate base

Answer 50

in aqueous solution

Question 51

when can the colour change of an indicator assumed to be distinguishable

Answer 51

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

Question 52

how can suitable indicators be selected

Answer 52

from pH data, including titration curves

Question 53

what occurs in a basic buffer when a small amount of base is added

Answer 53

the conjugate acid provided by the salt supplies hydrogen ions when these are removed by the addition of the base

Question 54

what occurs in an acidic buffer when a small amount of acid is added

Answer 54

the salt of the weak acid provides the conjugate base which can absorb excess hydrogen ions produced by the addition of a small amount of base