Chemical Equilibria Flashcards
When is a chemical reaction in dynamic equilibrium?
When the rate of the forward reaction and reverse reaction is equal.
What is the equilibrium constant?
It characterises the equilibrium composition of the reaction mixture.
What is the general equation of the equilibrium constant?
aA +bB >< cC + dD
What is the equilibrium expression?
K = (C)^c(D)^d/(A)^a(B)^b
What is homogenous equilibria?
Where all the substances are in the same phase.
What is heterogeneous equilibria?
Where the substances are in different phases
What is the concentration of pure solids and pure liquids at equilibrium?
Taken as a constant value of one in the equilibrium expression.
What does the numerical value of the equilibrium constant depend on?
Only on the reaction temperature and independent of the concentration and/or pressure.
What happens to the equilibrium constant (K) value in exothermic reactions?
A rise in temperature causes a decrease in the K value and the yield of product is decreased.
What happens to the equilibrium constant (K) value in endothermic reactions?
A rise in the temperature results in an increase in the K value and the yield of product is increased.
What happens to the equilibrium constant value in the presence of a catalyst.
The presence of a catalyst does not affect the value of the equilibrium constant.
What is the equation of the ionisation of water?
2H2O><H3O^+ + OH^-
What is a hydronium ion?
H3O^+ represents a hydronium ions, a hydrated proton.
What is amphoteric and give example of a substance that is.
Amphoteric is a substance that can act as an acid and base and an example of this is water.
What is the dissociation constant of water?
Known as the ionic product and is Kw = (H3O^+)(OH^-)
What is the value of the dissociation constant of water?
25^oC is 1 x 10^-1
What is the relationship between the hydrogen ion concentration and pH?
pH = -log(H^+) and (H^+) = 10^-pH
What is the relationship between pH and pOH?
pH + pOH = 14
What is monoprotic?
Monoprotic is when only one proton (H^+) is formed e.g. HCl
What is diprotic?
Diprotic is when two protons are formed e.g. H2SO4
What is triprotic?
Triprotic is when three protons are formed e.g. H3PO4
What are the Bronsted- Lowry definitions of acids and bases?
Acids are proton donors and bases are proton acceptors.
What does the acid form?
For every acid there is a conjugate base, formed by the loss of a proton.
What does the base form?
For every base there is a conjugate acid, formed by the gain of a proton
What are strong acids and bases?
Those that completely ionise (dissociate) into ions when dissolved in water.
What are some examples of strong acids and bases?
Acids include hydrochloric, sulfuric and nitric acid
Bases include metal hydroxides
What are weak acids and bases?
Partially ionised (dissociated) when dissolved in water.
What are some examples of weak acids and bases?
Acids include Ethanoic acid, carbonic acid and sulfurous acid
Bases include Ammonia and amines
What are the properties of a strong acid?
High conductivity, Fast reaction rate, lower pH and same volume to neutralise alkali.
What are the properties of a weak acid?
Lower conductivity, lower rate of reaction, higher pH and same volume to neutralise alkali.
What is the acid dissociation constant?
Ka = (H3O^+)(A^-)/(HA)
What does a soluble salt of a strong acid and a strong base dissolves in water produce?
A neutral solution
What does soluble salt of a weak acid and a strong base dissolves in water to produce?
A alkaline solution
What does a soluble salt of a strong acid and a weak base dissolves in water to produce?
An acidic solution
What is a buffer solution?
One that resists a change in pH when moderate amounts of an acid or base added to it.
What does an acidic buffer consist of?
a Solution of a weak acid and a salt from a strong base
What happens to a buffer in the addition of an acid?
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.
What is a basic buffer?
Consists of a solution of a weak base and a salt from a strong acid.
What happens to a buffer in the addition of an acid?
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
What are indicators?
They are used in acid-base titrations as they change colour at the end-point of the reaction
How is the colour of the indicator determined?
Determined by the ration of (In^-) : (HIn)
When is colour of indicator distinguishable?
The colour change is assumed to be distinguishable when
(HIn) and (In^-) differ by a factor of 10.
