Chemical Equilibria

Question 1

When is a chemical reaction in dynamic equilibrium?

Answer 1

When the rate of the forward reaction and reverse reaction is equal.

Question 2

What is the equilibrium constant?

Answer 2

It characterises the equilibrium composition of the reaction mixture.

Question 3

What is the general equation of the equilibrium constant?

Answer 3

aA +bB >< cC + dD

Question 4

What is the equilibrium expression?

Answer 4

K = (C)^c(D)^d/(A)^a(B)^b

Question 5

What is homogenous equilibria?

Answer 5

Where all the substances are in the same phase.

Question 6

What is heterogeneous equilibria?

Answer 6

Where the substances are in different phases

Question 7

What is the concentration of pure solids and pure liquids at equilibrium?

Answer 7

Taken as a constant value of one in the equilibrium expression.

Question 8

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

Answer 8

Only on the reaction temperature and independent of the concentration and/or pressure.

Question 9

What happens to the equilibrium constant (K) value in exothermic reactions?

Answer 9

A rise in temperature causes a decrease in the K value and the yield of product is decreased.

Question 10

What happens to the equilibrium constant (K) value in endothermic reactions?

Answer 10

A rise in the temperature results in an increase in the K value and the yield of product is increased.

Question 11

What happens to the equilibrium constant value in the presence of a catalyst.

Answer 11

The presence of a catalyst does not affect the value of the equilibrium constant.

Question 12

What is the equation of the ionisation of water?

Answer 12

2H2O><H3O^+ + OH^-

Question 13

What is a hydronium ion?

Answer 13

H3O^+ represents a hydronium ions, a hydrated proton.

Question 14

What is amphoteric and give example of a substance that is.

Answer 14

Amphoteric is a substance that can act as an acid and base and an example of this is water.

Question 15

What is the dissociation constant of water?

Answer 15

Known as the ionic product and is Kw = (H3O^+)(OH^-)

Question 16

What is the value of the dissociation constant of water?

Answer 16

25^oC is 1 x 10^-1

Question 17

What is the relationship between the hydrogen ion concentration and pH?

Answer 17

pH = -log(H^+) and (H^+) = 10^-pH

Question 18

What is the relationship between pH and pOH?

Answer 18

pH + pOH = 14

Question 19

What is monoprotic?

Answer 19

Monoprotic is when only one proton (H^+) is formed e.g. HCl

Question 20

What is diprotic?

Answer 20

Diprotic is when two protons are formed e.g. H2SO4

Question 21

What is triprotic?

Answer 21

Triprotic is when three protons are formed e.g. H3PO4

Question 22

What are the Bronsted- Lowry definitions of acids and bases?

Answer 22

Acids are proton donors and bases are proton acceptors.

Question 23

What does the acid form?

Answer 23

For every acid there is a conjugate base, formed by the loss of a proton.

Question 24

What does the base form?

Answer 24

For every base there is a conjugate acid, formed by the gain of a proton

Question 25

What are strong acids and bases?

Answer 25

Those that completely ionise (dissociate) into ions when dissolved in water.

Question 26

What are some examples of strong acids and bases?

Answer 26

Acids include hydrochloric, sulfuric and nitric acid Bases include metal hydroxides

Question 27

What are weak acids and bases?

Answer 27

Partially ionised (dissociated) when dissolved in water.

Question 28

What are some examples of weak acids and bases?

Answer 28

Acids include Ethanoic acid, carbonic acid and sulfurous acid Bases include Ammonia and amines

Question 29

What are the properties of a strong acid?

Answer 29

High conductivity, Fast reaction rate, lower pH and same volume to neutralise alkali.

Question 30

What are the properties of a weak acid?

Answer 30

Lower conductivity, lower rate of reaction, higher pH and same volume to neutralise alkali.

Question 31

What is the acid dissociation constant?

Answer 31

Ka = (H3O^+)(A^-)/(HA)

Question 32

What does a soluble salt of a strong acid and a strong base dissolves in water produce?

Answer 32

A neutral solution

Question 33

What does soluble salt of a weak acid and a strong base dissolves in water to produce?

Answer 33

A alkaline solution

Question 34

What does a soluble salt of a strong acid and a weak base dissolves in water to produce?

Answer 34

An acidic solution

Question 35

What is a buffer solution?

Answer 35

One that resists a change in pH when moderate amounts of an acid or base added to it.

Question 36

What does an acidic buffer consist of?

Answer 36

a Solution of a weak acid and a salt from a strong base

Question 37

What happens to a buffer in the addition of an acid?

Answer 37

In an acid buffer solution 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 38

What is a basic buffer?

Answer 38

Consists of a solution of a weak base and a salt from a strong acid.

Question 39

What happens to a buffer in the addition of an acid?

Answer 39

In a basic buffer solution the weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed

Question 40

What are indicators?

Answer 40

They are used in acid-base titrations as they change colour at the end-point of the reaction

Question 41

How is the colour of the indicator determined?

Answer 41

Determined by the ration of (In^-) : (HIn)

Question 42

When is colour of indicator distinguishable?

Answer 42

The colour change is assumed to be distinguishable when (HIn) and (In^-) differ by a factor of 10.