thermodynamics1 -equilibrium Flashcards
(18 cards)
activity definition
effective concentration or availability of a substance that accounts for non ideality
what is activity at standard conditions?
=1
for equilibrium A <-> B, how do we determine G and ΔG at standard and non standard conditions?
at standard conditions:
Ga = Ga (standard) (same for B)
so ΔG(standard) = Gb(st.)-Ga(st.)
at other conditions:
Ga = Ga(st.) + RT ln(aa) (same for B)
^ this allows us to account for deviation based on conditions/activity of a/b)
therefore
ΔG = ΔG(st.) + RT ln (ab) - ln(aa) = 0 because were at equilibrium, RT only needs to be accounted for once
for reaction A(l) <-> A(g) , what is
aA(g)/aA(l) equal to?
= the vapour pressure of saturated vapour, also the equilibrium constant
for reaction A(s) <-> A(aq) , what is
A(s)/A(aq) equal to?
= the concentration of saturated solution, also the equilibrium constant
how does G change throughout a reaction?
G falls as reaction progresses, so ΔG<0, until equilibrium, which is the minimum point on a gibbs energy vs reactant/product mole fraction graph, as its where gradient (ΔG) = 0
after the equilibrium point, G rises is the forward reaction proceeds further, to ΔG>0
chemical potential, μ definition
the energy that can be absorbed/released due to the change of the particle number of the given species, or how gibbs energy changes in a reaction
outline the relationship between equilibrium constant K and reaction quotient Q
for a reaction A <-> B
activity(A)/activity(B) = K at equilibrium and = Q when not at equilibrium
if Q=K reaction is at equilibrium
if Q<K there is more/too much reactant
if Q>K there is more/too much product
any change in the system will move to bring Q towards K, either via forwards or backwards reaction
for ΔG, ΔG(st.), Q and K:
what happens if reaction composition changes?
what happens if temp changes?
if composition change, only ΔG and Q will change, ΔG(st.) and K are constant
however change in temperature will change all of them
hess’s law definition
‘regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes’
state function definition + example
a state function is a variable that purley depends on the start and end/ the change between these two states, not the route taken
e.g. enthalpy
standard enthalpy of formation definition
the enthalpy change at 298.15K when 1 mole of a compound is formed under standard conditions from its consistent elements in their standard states
standard enthalpy of combustion definition
enthalpy change at 298.15K when 1 moles of a compound reacts completely with O2(g) at 1 bar pressure - always -ve
Sm(st.) definition
standard molar entropy of a compound (interchangeable with entropy)
give the equation for ΔH in relation to bond energy
ΔrH(st.) = + bonds broken - bonds formed
explain the composition of mixtures of volatile liquids
for a mixture containing 2 components, A and B, in 2 phases, liquid and gas, phases can have different compositions which can also be different form the composition of the overall mixture
- within this mixture A and B are in equilibrium between gas and liquid
what does it mean if liquid and gas of the same compound are in equilibrium?
means gas is saturated vapour
what does it mean if a point on a phase diagram is close to a phase boundary?
the closer the point on the phase diagram is to a phase boundary, the more of that phase is present in the mixture
