Chemical Equilibrium Flashcards
What is a “Dynamic Equilibrium” ?
When the rate of the forward and reverse reactions are constant and equal
What are the concentrations of products and reactants like at Dynamic Equilibrium?
The concentrations are constant but not necessarily equal.
When is a chemical reaction in equilibrium?
When the composition of the reactants and products remain constant indefinitely.
What does the equilibrium constant ( K ) show?
It characterises the equilibrium composition of the reaction mixture.
For the general reaction:
aA + bB ⇌ cC + dD
What is the equilibrium expression?
K = [C]c [D]/[A]a [B]b
(lower case are powers)
What does the equilibrium constant indicate?
The position of Equilibrium
(its a ratio)
What are the units of equilibrium constant?
It has no units
What is the concentration of pure solids and liquids taken as in the equilibrium expression?
Pure solids and liquids are taken as constant and given a value of 1
What is the numerical value of the equilibrium constant dependent on?
It depends on the reaction temperature and is independent of concentration and/or pressure.
How does a rise in temperature effect K and the product yield in an endothermic reaction?
A rise in temperature will cause an increase in K and increase the product yield.
How does a rise in temperature effect K and the product yield in an exothermic reaction?
A rise in temperature will cause a decrease in K and decrease the product yield.
How does the presence of a catalyst effect the equilibrium constant?
A catalyst does not effect the value of equilibrium constant.
When is there an equilibrium between the water molecules and hydronium (hydrogen) and hydroxide ions?
In water and aqueous solutions
What is the ionisation of water represented by?
H2O (l) + H2O (l) ⇌ H30+ (aq) + OH- (aq)
What does it mean when it is stated that water is amphoteric?
Water can react as an acid and a base.
Equimolar solutions of weak and strong acids (or bases) the same stoichiometry but different…
pH values, conductivity and reaction rates.
What is the acid dissociation constant represented by?
Ka or pKa
What does the soluble salt of a strong acid and a strong base dissolve in water to produce?
A Neutral solution
What does the soluble salt of a weak acid and strong base dissolve in water to produce?
An Alkaline solution
What does the soluble salt of a strong acid and a weak base dissolve in water to produce?
An acidic solution
What does the name of a salt produced depend on?
The acid and base used to produce it
How can the changes in concentrations of H3O+ and OH- ions of salt solutions be explained?
By using the appropriate equilibria
What is a buffer solution?
A solution in which the pH remains approximately constant when small amounts of acid, base or water are added.
Explain how an acid buffer solution works
In an acidic 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 a conjugate base which can absorb excess hydrogen ions produced by the addition of a small amount of acid.
What does a basic buffer consist of?
A weak base and one of its salts
How does a basic buffer solution work?
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.
How can indicators that are weak acids for which the dissociation be represented as?
HIn (aq) + H2O (l) ⇌ H3O+ (aq) + In- (aq)
What is the acid indicator of dissociation constant represented as (symbol)?
K In
In an aqueous solution what about an acid is distinctly different from that of its conjugate base?
Its colour
What is the colour of an indicator determined by?
The ratio of [H In] to [In-]
What is the theoretical point at which the colour change of an indicator occurs?
When [H3O+] = K In
When is the colour change of an indicator assumed to be distinguishable?
When [H In] and [In-] differ by a factor of 10
Which expression is used to estimate the pH range over which a colour change of an indicator occurs?
pH = p K In ± 1
What can be used to select a suitable indicator?
pH data, including titration curves
