2.1 chemical equilibrium Flashcards
when is a chemical reaction in equilibrium
when the composition of the reactants and products remains constant indefinitely
what is K
the equilibrium constant
what does the equilibrium constant do
characterises the equilibrium composition of the reaction mixture
what are A, B, C, D in the equilibrium expression
the equilibrium concentrations
what are a,b,c,d in the equilibrium expression
the stoichiometric coefficients
can the value of K be calculated
yes
what does the value of K indicate
the position of the equilibrium
what are the units for K
there aren’t units for K
what are the concentrations of pure solids and pure liquids at equilibrium taken as
constant
what value are the concentrations of pure solids and liquids at equilibrium given in the equilibrium expression
1
what does the numerical value of K depend on
the reaction temperature
can K be altered by concentration and/or pressure
no
what happens to the value of K if the temperature is increased during an endothermic reaction
increase
what happens to the value of K if the temperature is decreased in an endothermic reaction
decrease
what happens to the value of K if the temperature is increased during an exothermic reaction
decrease
what happens to the value of K if the temperature is decreased in an exothermic reaction
increase
does the presence of a catalyst affect the value of the equilibrium constant
no
what is there an equilibrium between - in water and aq solutions
there is one between the water molecules and hydronium and hydroxide ions
what is the equation for the ionisation of water
H2O + H2O -> H3O+ + OH-
what is the chemical formula for a hydronium ion
H3O+
what is a hydronium ion
a hydrated proton
what does amphoteric mean
it can react as an acid and a base
is water amphoteric? why can you conclude this?
yes, because it can react as an acid or as a base
what is the dissociation constant for the ionisation of water known as? what is it represented by?
it is known as the ionic product and it is represented by Kw
does the value of ionic product vary with temperature
yes
what is the value of Kw at 25 degrees (approx)
1x10-14
what is the Bronsted Lowry definition of acids and bases
an acid is a proton donor, and a base is proton acceptor
what is formed by the loss of a proton, for every acid?
a conjugate base
what is formed by the gain of a proton, for every base?
a conjugate acid
which type of acids and bases are completely dissociated into ions in aqueous solution
strong
which type of acids and bases are only partially dissociated into ions in aqueous solutions
weak
what are some examples of strong acids
- hydrochloric acid
- sulfuric acid
- nitric acid
what are examples of weak acids
- ethanoic acid
- carbonic acid
- sulfurous acid
what is an example of a strong base
solutions of metal hydroxides (eg sodium hydroxide)
what are examples of weak bases
ammonia and amines
how can the weakly acidic nature of some substances be explained
reference to the equations showing the equilibria
what are the differences between the equimolar solutions of weak and strong acids
- pH values
- conductivity
- reaction rates
what are the similarities between equimolar solutions of weak and strong acids
the stoichiometry of reactions are the same
what two acids and bases dissolve in water to produce neutral solutions
- strong acid and strong base
- weak acid and weak base
which acid and base dissolve in water to produce an alkaline solution
- weak acid and strong base
which acid and base dissolve in water to produce an acidic solution
strong acid and weak base
what does the name of the salt produced depend on
the acid and base used
what is a buffer solution
one in which the pH remains approx constant when small amounts of acid, base or water are added
what does an acid buffer consist of
a solution of a weak acid and one of its salts made from a strong base
what occurs in an acid buffer when a small amount of base is added
the weak acid provides hydrogen ions when these are removed by the addition of a small amount of base
what occurs in a basic buffer when an acid is added
the weak base removes excess hydrogen ions
how can an approx pH of an acid buffer solution be calculated
from its composition and from the acid dissociation constant
what are indicators
weak acids
what does Kin represent
the acid indicator dissociation
when in the colour of an acid indicator distinctly different from that of its conjugate base
in aqueous solution
when can the colour change of an indicator assumed to be distinguishable
when [HIn] and [In-] differ by a factor of 10
how can suitable indicators be selected
from pH data, including titration curves
what occurs in a basic buffer when a small amount of base is added
the conjugate acid provided by the salt supplies hydrogen ions when these are removed by the addition of the base
what occurs in an acidic buffer when a small amount of acid is added
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
