7. Chemical equilibria, the equilibrium constant and the degree of dissociation, their correlation. The Le Châtelier principle Flashcards
7. Chemical equilibria, the equilibrium constant and the degree of dissociation, their correlation. The Le Châtelier principle
What is Chemical equilibrium?
the state wherein the rate of the forward reaction is equal to the rate of the reverse reaction.
What is an equilibrium constant?
The constant that relates the concentrations of reactants and products at equilibrium.
Does the value of an equilibrium constant increase or decrease when reaction temperature is increased? How?
For reactions where the forward reaction is exothermic, the equilibrium constant decreases with increasing temperature.
For reactions where the forward reaction is endothermic, the equilibrium constant increases with increasing temperature
What is Equilibrium position?
The relative amounts of reactants and products present in a system at equilibrium define the equilibrium position
When is Equilibrium position toward the right?
when a large amount of product is present
When is Equilibrium position toward the right?
when a large amount of reactant is present
Value of Keq - very large (10^30)
Relative amount of products and reactants - ?
Description of equilibrium position - ?
- Relative amount of products and reactants → essentially all products
- Description of equilibrium position → far to the right
Value of Keq - large (10^10)
Relative amount of products and reactants - ?
Description of equilibrium position - ?
- Relative amount of products and reactants → more products than reactants
- Description of equilibrium position → to the right
Value of Keq - near unity (between 10^3 and 10^-3)
Relative amount of products and reactants - ?
Description of equilibrium position - ?
- Relative amount of products and reactants → Significant amount of both reactants and products
- Description of equilibrium position → neither to the right nor to the left
Value of Keq - small (10^-10)
Relative amount of products and reactants - ?
Description of equilibrium position - ?
- Relative amount of products and reactants → more reactants than products
- Description of equilibrium position → to the left
Value of Keq - very small (10^-30)
Relative amount of products and reactants - ?
Description of equilibrium position - ?
- Relative amount of products and reactants → essentially all reactants
- Description of equilibrium position → far to the left
State Le Châtelier’s principle
when a stress (change of conditions) is applied to a system in equilibrium, the system will readjust (change the equilibrium position) in the direction that best reduces the stress imposed on it.
4 type of stresses that change an equilibrium position
(1) changes in amount of reactants and/or products
(2) changes in temperature
(3) changes in pressure
(4) addition of catalysts
What is law of mass action?
The rate of a chemical reaction (change in concentration per unit time) generally increases when the concentrations of the reactants increase.
What happen if we add substance to the right side (C or D)?
The reaction proceeds to the left (C and D consumed, A and B produced) until Q = Keq
What happen if we take substance from the right side (C or D)?
The reaction proceeds to the right (A and B consumed, C and D produced) until Q = Keq again.
What happen if we add substance to the left side (A or B)
Add substance to the left side (A or B) – A is added = pressure increases
→ The reaction proceeds to the right (A and B consumed, C and D produced) until pressure decreases
What happen if we increase temperature?
The reaction proceeds to the left (heat is absorbed) until Q and Keq are adjusted, temperature decreases
What is degree of dissociation? Give the formula
- The fraction of the total concentration of a weak electrolyte that is in ionic form in aqueous solution at equilibrium
- degree of dissociation = [ionized] / [non-ionized]
