7. chemical equilibria

ICE table

Initial concentration/

Change in concentration/

Equilibrium concentration/

*uses units of mol, mol dm-1, pressure (Pa/kPa/atm/bar)

Le Chatelier’s Principle

Le Chatelier’s Principle states that when a system at equilibrium is subjected to a change, the system will react to counteract the change imposes to as to reestablish the equilibrium.

Reversible reactions

Reversible reactions are reactions that proceed in both the forward and backward reactions.

details:

• denoted by double headed arrow

• never complete, they only achieve a state of dynamic equilibrium where neither reactant or product conc reach 0

Dynamic equilibrium

Dynamic equilibrium refers to a state in a reversible system within a closed system in which the forward and backward reactions are continuing at the same rate, resulting in no net change in the macroscopic properties (e.g. concentrations, partial pressure) of the reactants and products.

details:

• only attained in closed system

• can be attained from either direction, with any amount of reactants and products, as long as TEMPERATURE is constant (equilibrium is temp sensitive)

Kc

The equilibrium constant, which is the value of reaction quotient (Qc) when dynamic equilibrium is achieved at a given temperature.

For aA + bB <=> cC + dD, with all concentrations at equilibrium,

Kc = [(conc C)^c(conc D)^d]/[(conc A)^a(conc B)^b]

Qc is the same, but with concentrations at any given time