Key Terms
Start with only products
Same process in reverse.
Law of Mass Action
At a given temperature, Q for a system at equilibrium is always K. This is the formal statement of why K is constant.
Homogeneous
All species in the same phase (all aqueous, all gas).
Heterogeneous
Species in two or more phases (solid + gas, solid + aqueous).
Example
N2(g) + 3H2(g) = 2NH3(g) Reactant side: 4 moles gas. Product side: 2 moles gas.
Conversion formula
Kp = Kc(RT)^delta-n
Add reactant or remove product
Q drops below K; shift right. Remove reactant or add product: Q rises above K; shift left.
If moles of gas are unequal
System shifts toward the side with fewer moles of gas when pressure increases; shifts toward the side with more moles wh
Endothermic reaction (absorbs heat)
Treat heat as a reactant.
Exothermic reaction (releases heat)
Treat heat as a product.
Problem
Product must be removed continuously. Solution: continuously remove NH3 to keep Q below K and drive the reaction forward
Assumption
If initial concentration is [A]0 and change is x; treat ([A]0 - x) as approximately [A]0.
Kc
Equilibrium constant expressed in molar concentrations.
Kp
Equilibrium constant expressed in partial pressures.
ICE table
Initial-Change-Equilibrium; systematic method for equilibrium calculations.