2.1 - Chemical Equilibrium

Question 1

what is meant by a chemical reaction in equilibrium in terms of composition?

Answer 1

the composition of reactants and products

Question 2

what is the symbol for equilibrium constant?

Answer 2

K

Question 3

what do the lower case letters in the K equation represent?

Answer 3

the stoichiometric coefficients

Question 4

what value of concentration is given to pure solids and liquids in an equilibrium expression?

Answer 4

1

Question 5

which of these factors influence the value of equilibrium constant?
temperature
concentration
pressure

Answer 5

temperature

Question 6

for an exothermic reaction, a rise in temperature leads to what?

Answer 6

a decrease in K and a decrease in product yield

Question 7

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

Answer 7

it doesn’t

Question 8

what equilibrium exists in water and aqueous solutions

Answer 8

water molecules - hydronium (hydrogen) and hydroxide ions

Question 9

what is meant by amphoteric

Answer 9

a species able to react as an acid and a base

Question 10

state the equation for the ionisation of water (the equilibrium in water and aqueous solutions)

Answer 10

H₂O(l) + H₂O(l) - H₃O⁺ (aq) + OH⁻

Question 11

show the chemical formula for a hydronium ion, and the shorthand formula.

Answer 11

H₃O⁺ (aq) H⁺ (aq)

Question 12

give an example of an amphoteric species

Answer 12

water

Question 13

what is the dissociation constant for the ionisation of water, also known as?

Answer 13

the ionic product

Question 14

with what condition does the ionic product vary

Answer 14

temperature

Question 15

what is the value of Kᵥᵥ at 25ᵒ C

Answer 15

1x10⁻¹⁴

Question 16

what is the concentration of H₃O⁺ and OH⁻ ions in water, with a pH of 7, at 25C

Answer 16

10⁻⁷ moll

Question 17

state the Bronsted-Lowry definition of acids and bases

Answer 17

a base is any species which can accept a proton

an acid is any species which can donate a proton

Question 18

what is a conjugate base?

Answer 18

the base formed by the loss of a proton, when an acid is formed

Question 19

what is a conjugate acid?

Answer 19

the acid formed by the gain of a proton, when a base is formed

Question 20

what is a strong acid/base?

Answer 20

a compound which is completely dissociated into its ions in aqueous solution

Question 21

what is a weak acid/base?

Answer 21

a compound which is partially dissociated into its ions in aqueous solution

Question 22

state the examples of strong acids and their formulae

Answer 22

hydrochloric acid HCl, sulfuric acid H2SO4 and nitric acid HNO3

Question 23

state the examples of weak acids

Answer 23

ethanoic acid CH3COOH, carbonic acid H2CO3 and sulfurous acid H2SO3

Question 24

state the examples of strong bases

Answer 24

metal hydroxides

Question 25

state the examples of weak bases

Answer 25

ammonia and amines

Question 26

what properties are different between strong/weak acid/bases

Answer 26

pH values, conductivity and reaction rates

Question 27

the soluble salt produced in a reaction between a strong acid and a weak base, would result in what type of solution

Answer 27

acidic

Question 28

what is a buffer solution

Answer 28

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

Question 29

what does an acid buffer consist of

Answer 29

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

Question 30

explain how an acid buffer works

Answer 30

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

Question 31

what does a basic buffer consist of

Answer 31

a solution of a weak base and one of its salts

Question 32

explain how a basic buffer works

Answer 32

the weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed.

Question 33

indicators are weak what

Answer 33

acids

Question 34

what ratio determines the colour of an indicator

Answer 34

[HIn} to [In-]

Question 35

when is the theoretical point of colour change

Answer 35

when [H3O+] = Kin

Question 36

by what factor is colour change assumed to be distinguishable

Answer 36

10

Question 37

what is the standard enthalpy of formation

Answer 37

the enthalpy change when one mole of a substance is formed from its elements in their standard states

Question 38

what is the standard state of a substance

Answer 38

s its most stable state at a pressure of 1 atmosphere and at a specified temperature, usually taken as 298 K

Question 39

what is the entropy(S) of a system

Answer 39

a measure of the degree of disorder of a system

Question 40

a higher disorder means a ……entropy

Answer 40

higher

Question 41

how does entropy change with temperature

Answer 41

entropy increases

Question 42

when do rapid and even more rapid increases in entropy occur

Answer 42

at the melting point of a substance, and the boiling point

Question 43

what does the 2nd law of thermodynamics state

Answer 43

the total entropy of a reaction system and its surroundings always increases for a spontaneous process

Question 44

what does the 3rd law of thermodynamics state

Answer 44

the entropy of a perfect crystal at 0 K is zero

Question 45

If the change in free energy between reactants and products is negative, a what may occur

Answer 45

a reaction may occur and the reaction is said to be feasible.

Question 46

what is a feasible reaction

Answer 46

A feasible reaction is one that tends

towards the products rather than the reactants. This does not give any indication of the rate of the reaction.

Question 47

under non-standard conditions, any reaction is feasible if…

Answer 47

delta G is negative

Question 48

what is the value of delta G at equilibrium

Answer 48

0