Lecture Sixteen - Equilibria Flashcards
Define molarity and molality.
Molarity (M) = A 1 molar aqueous solution contains 1 mole of solute in 1000mL of solution.
Molality (m) = A 1 molal aqueous solution contains 1 mole of solute in 1000g of solvent (not temperature dependant, unlike M).
These concentration units assume there are no interactions between solute and solvent species.
How is the thermodynamic equilibrium constant, K defined?
Define the various equilibrium constants.
Kc = The general equilibrium constant (also K).
Kp = The equilibrium contant in terms of pressure for those reactants with (under) pressure.
Ka = The acid dissociation contant, always seen around acids (Kb for base).
Kw = The water self-ionisation constanrt, loves to get involved with Ka and Kb.
Ksp = The solubility product constant, used when we have salts that hardly dissolve.
Kstab (or β) = The overall stability constant, used when things start getting complex.
Explain how the equilibrium contant, Kp, is used.
If the species are in the gas phase, their activity is approximatly equal to the numerical value of their partical pressures (measured in bar, 1 bar = 10^5 Pa).
In general for any reaction at equilibrium, the equilibrium constant in terms of pressure is spprocimated as:
How are Kc and Kp related? (Equation).
Through concentration and pressure:
How can Kp be calculated?
What is the reaction quotient (Q)?
The reaction quotient defines the extent and direction of a reaction at any time before equilibrium is reached.
Until Q = K, the reaction is still moving in one direction, and the concentration of reactants and productres is changing.
As a reaction proceeds, the value of Q changes.
If Q = K, reaction is at equilibrium.
If Q > K, the reaction moves towards the reactants (left).
If Q < K, the reaction moves towards the products (right).
What is the connection between thermodynamics (Gibbs Free Energy, more specifically) and equilibria? (Graph).
Note that the delta G where gradient is positive should be where delta G is > 0, i.e. reaction is non-spontaneous.
What is the relationship between thermodynamics and equilibria? (Equation).
The Gibbs Free Energy under standard conditions has the label, ΔGr°.
The free energy change under any conditions, ΔGr°, is related to ΔGr° and Q by:
This reaction is known as the reaction isotherm.
In its exponential form:
K = e- (ΔGr°/RT)
By using this reaction we can make observations about whether the reactants or products are favoured in a reaction.
If ΔGr° > 0 , then K < 1, so reactants are favoured.
If ΔGr° < 0, then K > 1, so products are favoured.
