2.1 - Chemical Equilibrium Flashcards
what is meant by a chemical reaction in equilibrium in terms of composition?
the composition of reactants and products
what is the symbol for equilibrium constant?
K
what do the lower case letters in the K equation represent?
the stoichiometric coefficients
what value of concentration is given to pure solids and liquids in an equilibrium expression?
1
which of these factors influence the value of equilibrium constant?
temperature
concentration
pressure
temperature
for an exothermic reaction, a rise in temperature leads to what?
a decrease in K and a decrease in product yield
how does the presence of a catalyst affect the value of the equilibrium constant
it doesn’t
what equilibrium exists in water and aqueous solutions
water molecules - hydronium (hydrogen) and hydroxide ions
what is meant by amphoteric
a species able to react as an acid and a base
state the equation for the ionisation of water (the equilibrium in water and aqueous solutions)
H₂O(l) + H₂O(l) - H₃O⁺ (aq) + OH⁻
show the chemical formula for a hydronium ion, and the shorthand formula.
H₃O⁺ (aq) H⁺ (aq)
give an example of an amphoteric species
water
what is the dissociation constant for the ionisation of water, also known as?
the ionic product
with what condition does the ionic product vary
temperature
what is the value of Kᵥᵥ at 25ᵒ C
1x10⁻¹⁴
what is the concentration of H₃O⁺ and OH⁻ ions in water, with a pH of 7, at 25C
10⁻⁷ moll
state the Bronsted-Lowry definition of acids and bases
a base is any species which can accept a proton
an acid is any species which can donate a proton
what is a conjugate base?
the base formed by the loss of a proton, when an acid is formed
what is a conjugate acid?
the acid formed by the gain of a proton, when a base is formed
what is a strong acid/base?
a compound which is completely dissociated into its ions in aqueous solution
what is a weak acid/base?
a compound which is partially dissociated into its ions in aqueous solution
state the examples of strong acids and their formulae
hydrochloric acid HCl, sulfuric acid H2SO4 and nitric acid HNO3
state the examples of weak acids
ethanoic acid CH3COOH, carbonic acid H2CO3 and sulfurous acid H2SO3
state the examples of strong bases
metal hydroxides
state the examples of weak bases
ammonia and amines
what properties are different between strong/weak acid/bases
pH values, conductivity and reaction rates
the soluble salt produced in a reaction between a strong acid and a weak base, would result in what type of solution
acidic
what is a buffer solution
a solution in which the pH remains approximately 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
explain how an acid buffer works
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 does a basic buffer consist of
a solution of a weak base and one of its salts
explain how a basic buffer works
the weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed.
indicators are weak what
acids
what ratio determines the colour of an indicator
[HIn} to [In-]
when is the theoretical point of colour change
when [H3O+] = Kin
by what factor is colour change assumed to be distinguishable
10
what is the standard enthalpy of formation
the enthalpy change when one mole of a substance is formed from its elements in their standard states
what is the standard state of a substance
s its most stable state at a pressure of 1 atmosphere and at a specified temperature, usually taken as 298 K
what is the entropy(S) of a system
a measure of the degree of disorder of a system
a higher disorder means a ……entropy
higher
how does entropy change with temperature
entropy increases
when do rapid and even more rapid increases in entropy occur
at the melting point of a substance, and the boiling point
what does the 2nd law of thermodynamics state
the total entropy of a reaction system and its surroundings always increases for a spontaneous process
what does the 3rd law of thermodynamics state
the entropy of a perfect crystal at 0 K is zero
If the change in free energy between reactants and products is negative, a what may occur
a reaction may occur and the reaction is said to be feasible.
what is a feasible reaction
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.
under non-standard conditions, any reaction is feasible if…
delta G is negative
what is the value of delta G at equilibrium
0
