CHEM 14A Study Guide - Final Guide: Reaction Quotient, Inert Gas, Lone Pair
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19 Aug 2019
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Ch. 11: Equilibrium
Chemical Equilibrium
● Rate of forward rxtn = rate of reverse rxtn
● Dynamic equilibrium: although it seems as though the reaction has stopped, at the
molecular level, the reactions are still occurring
○ Homogenous equilibrium: reactants and products in the same phase
○ Heterogeneous equilibrium: one or more reactant or product in a diff phase
● If K= 10-3-103 → equilibrium is favored
● Molar concentration of a pure substance (solid or liquid) doesn’t change, so they don’t
participate in equilibrium equations
● Q: reaction quotient, at any time during the reaction
● ICE tables: not yet at equilibrium, need to solve to see when the equilibrium will be
If calculated value of x is smaller than 5% of the initial values, solve by approximation:
Replace A + x or A - 2x with just A
Le Chatelier's Principle
● If there is a stress to system at equilibrium, the reaction will try to minimize it
● Catalyst: doesn’t change anything, only helps reaction get to equilibrium quicker
● Change in pressure by adding inert gas: doesn’t affect the volume or reaction
● Change in temperature: change in equilibrium constant
Ch. 12: Acids and Bases
Bronsted Acids and Bases
● Acids: proton donor (H+ donor)
○ Strong: completely ionizes in solutions (dissociates)
■ HBr, HCl, H2SO4, HNO3, HClO4 (perchloric), HClO3 (chloric)
○ Weak: incompletely ionized in solution. Needs an equilibrium to calculate
concentrations
● Bases: proton acceptor (H+ acceptor), with lone pair
○ Strong: completely dissociated in solution
■ Group 1 and 2 hydroxides
■ Group 1 and 2 oxides
○ Weak: not completely ionized in solution, sets up an equilibrium
Lewis Acids and Bases
● Acids: electron pair acceptor
○ H+ is a lewis acid
○ Small, highly metal cations can act as lewis acids ex. Fe3+, Cr3+
○ Cations from group 1 and 2 are weak lewis acids
● Bases: electron pair donor
Amphoteric Compound
● Can act as an acid or a base
● Ex. water and around the metalloid section
Amphiprotic
● Proton donor and acceptor
● Water
Water in autoprotolysis: 2 H2O ↔ OH- + H3O+
● Kw=10-14=[OH-][H3O+]
○ pH=-log (H3O+)
○ pOH=-log (OH-)
● pKw=14=pH+pOH
● Pure water (any temperature): [H3O+]=[OH-]
● **Can only be assumed for strong acids and bases (100% dissociation)
Weak Acid-Base Equilibria
● Cannot assume 100% dissociated, so we use dissociation constants for weaks and ICE
● Kw=KaKb=10-14
● pKw=14=pKa+pKb
● HA + H2O ↔ H3O+ + A-
○ Ka=[H3O+][A-]/[HA]
○ Ka= acidity constant (the dissociation constant of an acid)
● B + H2O ↔ OH- + HB+
○ Kb=[OH-][HB+]/[B]
○ Kb=basic constant (the dissociation constant of a base)
Dissociation of weak acid=([A-]/[HA]) x 100%
Dissociation of weak base= ([BH+]/[B]) x 100%
Conjugate Seesaw
● HA + H2O ↔ H3O+ + A-
○ Acid: HA
○ Conjugate base: A-
■ Has one less H
■ Potential to be a proton acceptor
● B + H2O ↔ OH- + HB+
○ Base: B
○ Conjugate acid: HB+
■ Has one more H
■ Potential to lose the proton
● Kw=KaKb=10-14