Equilibrium Flashcards
What is meant by chemical equilibrium?
State in which the rate of forward reaction is equal to rate of reverse reaction
Why is chemical equilibrium described as a dynamic state?
Both reactions are continuously occurring, both continue
What is the law of mass action?
The rate of a chemical reaction is proportional to the active masses of the reacting substances.
What are ‘‘active masses’’
regard as concentrations of the participating
species or partial pressures in the case of gases.
What is the Equilibrium constant?
concentrations of products to the power of moles/concentrations of reactants to the power of moles
[C]c [D]d / [A]a [B]b
For each reaction, how does the value for Keg vary?
For each reaction, there is only one value for Keq at a specific temperature.
What are the characteristics of equilibrium?
Characteristics of equilibrium:
- Dynamic: balance of reversible reactions
- All reactants and products are present (both reactions can occur)
- Move to equilibrium is spontaneous – if disturbed then it returns to the same equilibrium point.
- Represents a compromise between DH (change in enthalpy taking the enthalpy to a minimum DS (change in entropy) taking the entropy to a maximum.
- constant only at a specific temperature
Is the move to equilibrium spontaneous?
Yes, if disturbed then it returns to the same equilibrium point.
What does the value of Keq tell us?
The extent to which reactants are converted into products.
Keq < 1: Reactants are favored at equilibrium
Keq > 1: Products are favored at equilibrium
For gases the concentration is proportional to what?
the partial pressure at a fixed temperature
If gases nA + nB are mixing, with a ratio of 2:1, what will happen?
Eventually will mix (two gases)
What is the molar concentration of the gas equal to?
its partial pressure divided by RT – and RT is constant at a given temperature. (n/V = P/RT)
Consider the following reaction involving gases:
2SO2(g) + O2(g) ⇄ 2SO3(g)
What is kP?
[Pso3]2 / [Pso2]2 [Po2]
What is the relationship between Kp and Kc
Kp = Kc (RT) ∆n
What is the relationship between the free energy change for a reaction G and the equilibrium constant for that reaction, K?
ΔG = - RTln K
Where ΔGo is the standard free energy change and may be written ΔGo = ΔHo- TΔS
o and ΔHo and ΔSo are standard enthalpy and entropy changes and may be determined experimentally.
Write the equilibrium constant expression of
N2O4 ->2NO2
[NO2]^2
———
[N2O4]
State Le Châtelier’s principle
If “stress” is applied to system at equilibrium, system reacts to relieve stress applied (Le Chatelier’s Principle ignores the presence of catalysts)
What are the factors that influence equilibrium?
Concentration, temperature, and partial pressure (for
gaseous)
A + B - C + D
What occurs when concentration of A increases?
System alters to minimise effect and equilibrium shifts to right and more of C and D produced
A + B - C + D
What occurs when concentration of C increases?
System alters to minimise effect, equilibrium shifts to left therefore more of A and B produced
A + B - C + D
What occurs when concentration of A decreases?
System alters to minimise effect, equilibrium shifts to left therefore more of A and B produced
A + B - C + D
What occurs when concentration of C decreases?
System alters to minimise effect, equilibrium shifts to right therefore more of C and D produced
What effect does an increase in pressure have?
[opposite - side with fewer molecules]
System alters to oppose stress to side with fewer molecules
What effect does a decrease in pressure have on an equilibrium reaction?
[think of opposite - side with more molecules]
The system alters to oppose stress, and moves to side with more molecules