7: Equilibrium Flashcards
Chemical equilibrium
The state of dynamic equilibrium that occurs in a closed system when the forward and reverse reactions of a reversible reaction occur at the same rate.
Characteristics of the equilibrium state
- dynamic
- equilibrium achieved in a closed system
- concentrations of reactants and products remain constant
- macroscopic properties don’t change
- equilibrium can be reacted from either direction
Comparing K_c values
K_c > 10^10
K_c = 100
K_c = 1
K_c = 0.01
K_c < 10^-10
K_c > 10^10: rxn goes almost to completion
K_c = 100: products predominate
K_c = 1: appreciate amount of both reactants and products
K_c = 0.01: reactants predominate
K_c < 10^-10: rxn hardly proceeds
Le Chatelier’s principle
When a system at equilibrium is disturbed, the equilibrium position will shift in the direction which tends to minimize or counteract the effect of the disturbance.
If Q < K_c…
If Q > K_c…
If Q = K_c…
…the reaction proceeds to the right
…the reaction proceeds to the left
…the reaction is at equilibrium
Factors that alter equilibrium
- Concentration
- Change in pressure for a gas phase reaction
- Change in temperature
In an endothermic reaction…
T increases
T decreases
Equilibrium shifts right, K_c increases
Equilibrium shifts left, K_c decreases
In an exothermic reaction…
T increases
T decreases
Equilibrium shifts left, K_c decreases
Equilibrium shifts right, K_c increases
Effect of catalyst on the equilibrium position
No effect, the use of a catalyst only affects the rate of the forward and backward reaction(s).
Industrial applications: Haber Process
Industrial production of ammonia (NH_3)
High pressure of about 250 atm, high temperature of about 450°C, Fe used as a catalyst.
Industrial applications: Contact process
Industrial production of sulphuric acid (SO_3)
Low pressure of about 2 atm, high temperature of about 450°C, vanadium (V) oxide used as a catalyst.
Industrial applications: Production of methanol, CH_3OH
High pressure of 5x10^6 Pa used, high temperature of 250°C, Cu-ZnO-Al_2O_3 used as a catalyst.
The pressure and temperature that favors the formation of products.
High pressure, low temperature
Homogeneous equilibrium
Equilibrium reactions where all reactants and products are in the same state; all gas, liquid, or aqueous.
The position of equilibrium corresponds to…
Maximum value of entropy and a minimum value of Gibbs free energy (ie. at equilibrium ΔG is equal to zero)
