Topic 7.1: Equilibrium Flashcards
Definition of Dynamic Equilibrium
State in which the rate of the forward reaction equals the rate of the backward reaction
Characteristics of equilibrium
a) Dynamic
b) Attained in a closed system
c) Constant concentration of reactants and products
d) No change in macroscopic properties
e) Achieved from either direction
Characteristics of equilibrium (Explanation)
a) Dynamic
The reaction has stopped but both forward and backward reactions are still occurring at the same rate.
Characteristics equilibrium (Explanation) b) Attained in a closed system
A closed system prevents exchange of matter with the surroundings, so it is achieved where both reactants and products can react and recombine.
Characteristics equilibrium (Explanation) c) Constant concentrations of reactants and products
They are being produced and destroyed at an equal rate.
Characteristics equilibrium (Explanation) d) No change in macroscopic properties
Color and density do not change as these depend on the concentrations.
Characteristics equilibrium (Explanation) e) Achieved from either direction
The reaction can be started with all reactants, all products or a mixture.
Example of physical equilibrium
a) In a closed system, Br2 (l) is in a dynamic equilibrium with its vapor.
b) There will always be both liquid and gas bromine in the flask.
c) Vaporization and condensation are both happening simultaneously in the flask.
d) Liquid bromine is in dynamic equilibrium with bromine vapour.
Example of chemical equilibrium
a) In a closed system, the rate of disassociation of HI is fastest at the start.
b) The reverse reaction, which initially has a zero-rate due to the lack of products, starts slowly and increases in rate as the concentrations of products increases.
c) The rate of disassociation of HI has become equal to the rate of the reverse reaction of association between H2(g) + I2 (g), so the concentrations remain constant.
Representation of Equilibrium Reaction
aA + bB ⇄ cC+ dD
Definition of the Equilibrium Constant
Ratio of concentrations of products over reactants for a reaction that is at equilibrium
Representation of Equilibrium Constant (Kc)
([C]^c {D]^d) / ([B]^b {A]^a)
What does the magnitude of Kc represent?
The extent of a reaction at equilibrium (Relative amounts of products or reactants)
If Kc»_space; 1, then equilbirium favors…
Products
If Kc «_space;1, then equilbirium favors…
Reactants
What would happen to the value of Kc for a particular reaction at a particular temperature if an environmental factor is modified?
Remains constant. THe system adjusts to keep the concentrations at equilibrium
What does the Chatelier’s principle state?
If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to re-establish an equilibrium:
What happens to the position of equilibrium if the pressure increases in a system?
It shifts the equilibrium to the side with fewer moles of gas
What happens to the position of equilibrium if the pressure decreases in a system?
It shifts the equilibrium to the side with more moles of gas
What happens to the position of equilibrium if a substance is added to a system at equilibrium?
The system reacts to consume some of the substance.
What happens to the position of equilibrium if a substance is removed from a system?
The system reacts to produce more of substance.
What happens to the position of equilibrium if a catalyst is added to a system?
No effect
What happens to the position of equilibrium if temperature is increased in a system?
The position of equilibrium shifts in the endothermic direction
What happens to the position of equilibrium if temperature is decreased in a system?
The position of equilibrium shifts in the exothermic direction.
Which environmental factor changes the value of Kc?
Temperature
How does temperature change the value of Kc for an exothermic reaction?
Kc decreases as the temperature is increased.
How does the temperature change the value of Kc for an endothermic reaction?
Kc increases as the temperature is increased.
Manipulation of Kc
a) Inverse reaction
b) Multiple of a reaction
c) Adding two reactions
a) 1 / K
b) K^n
c) (K1) (K2)
What does the reaction quotient measure?
Relative amounts of products and reactants present during a reaciton at a particular point in time.
Purpose of comparing Kc with Q
Determine the direction of the reaction
If Kc = Q, then…
The reaction is at equilibrium
If Kc > Q, then…
Q will increase and produce more products.
If Kc < Q, then…
Q will decrease and therefore create more reactants.
Chemical equation of Haber process
N2(g) + 3H2(g) ⇄ 2NH3(g)
Information of Haber process (3)
(a) All reactants and products are gases
(b) The forward reaction is exothermic so releases heat.
(c) Fe works as a catalyst
