Equilibrium Flashcards
Definition of a closed system
no exchange of matter with the surroundings
Definition of dynamic equilibrium.
rate of forward reaction = rate of reverse reaction
must be in a closed system
Draw a graph of rate against time of forward and reverse reactions to equilibrium
See page 2
What are features of equilibrium?
macroscopic properties are constant
rate of forward reaction = rate of reverse
closed system
all species in chemical equation will be present in equilibrium mixture
equilibrium can be attained from either direction
Definition of Phase Equilibrium.
When the rates of condensation and evaporation are equal
(bromine liquid in vacuum evaporates and condenses constantly)
How does increasing temperature affect the position of equilibrium?
favours endothermic direction
(in exam: p.o.e shifts to the …
yield of … increases/decreases)
What is Le Chatelier’s principle?
if a system at equilibrium is subjected to some change, the position of equilibrium will shift in order to minimise the effect of the change.
How does increasing pressure affect the position of equilibrium?
p.o.e shifts to the side with fewer moles of gas
(in exam: p.o.e shifts to the …
yield of … increases/decreases)
What is the effect of increasing the concentration of alkali on equilibrium?
alkali lowers [H⁺] through neutralisation
p.o.e shifts towards acid to replace the removed H⁺
How does using a solution affect the equilibrium?
a solution adds H₂O to the mixture
What does [A] mean?
concentration of A at equilibrium
Concentration =
mol/volume
How do you find the equilibrium constant for:
K = A + 2B <–> 3C + 4D
K = ([C]³[D]⁴) / ([A][B]²)
When do you use the equilibrium constant?
only for products and reactants in the same physical state
How to find how much products there are at equilibrium?
Use RICE:
Ratio
Initial
Change
Equilibrium
When do the equilibrium constants change?
With temperature
forward reaction and reverse reaction are different
What use is the equilibrium constant?
Tells us how far a reaction proceeds at a particular temperature
How does the equilibrium constant differ with temperature?
If K is much bigger than 1, is proceeds almost completely towards the products.
If K is much smaller than 1, it hardly proceeds to the products
If K = 1, position of equilibrium lies in the middle
What is the reaction quotient?
ratio of concentrations of the reactants and products at any point in time
How to find the reaction quotient, Q?
the same as K
How does Q show how far the reaction is towards equilibrium?
If Q<K, reaction must proceed to products to reach equilibrium
If Q>K, reaction must proceed to reactants to reach equilibrium
If the reaction vessel is halved in size at constant temperature, what happens to the concentration of each species?
they are doubled
What happens to the equilibrium constant as the temperature is raised?
Exothermic reaction:
value of K decreases
Endothermic reaction: value of K increases
How to know if a reaction is endothermic or exothermic based on values of K?
if T increases and K decreases:
when K decreases, p.o.e shifts left
when T increases, it favours endo reaction
so reverse reaction is endothermic
How do catalysts affect equilibrium?
increase the rate of forward and reverse reaction equally, so reduce time taken to reach equilibrium
doesn’t affect the position of equilibrium
What is the difference between K and k?
K – equilibrium constant
shows how far reaction goes towards completion (no information about how quickly reaction occurs)
k – rate constant
how quickly equilibrium is attained (no information about p.o.e and how far reaction proceeds)
What does -∆G show?
reaction is spontaneous
Draw a graph of gibbs energy on equilibrium?
See page 20
What does the equilibrium mixture represent?
the composition that gives the minimum value of the Gibbs energy
What does:
∆G = ∆G(^0 with a line through) + RTlnQ
∆G and ∆G(^0 with a line through) in J mol⁻¹ because R is in J K⁻¹ mol⁻¹
∆G(^0 with a line through) – from pure A to pure B (probably given to you)
Q – reaction quotient
R – constant
T – temperature in K
∆G – difference in Gibbs energy between amount of A present in reaction mixture and amount B present.
What happens to ∆G as a system moves towards equilibrium?
becomes less negative until it equals zero at equilibrium
What happens to ∆G when the system is at equilibrium?
it is 0 – doesn’t move spontaneously in either direction
When is the equation:
∆G(^0 with a line through) = -RTlnK
used?
when ∆G = 0
What does -∆G(^0 with a line through) show about the p.o.e?
lie closer to products than reactants
[products] > [reactants]
K > 1
What does +∆G (^0 with a line through) show about the p.o.e?
lie closer to reactants than products
[products] < [reactants]
K < 1
