physical-chemistry

# Physical Chemistry Physical chemistry answers three quantitative questions about a reaction: how far does it go, how fast does it go, and how much electrical work can it do? These map to equilibrium, kinetics, and electrochemistry. This skill covers the equations and problem-solving methods for all three, with worked examples throughout. **Agent affinity:** pauling (bonding and molecular energetics, primary), lavoisier (conservation, reaction bookkeeping, routing) **Concept IDs:** chem-equilibrium, chem-le-chatelier, chem-buffers-ksp, chem-kinetics, chem-arrhenius, chem-electrochemistry ## Chemical Equilibrium At equilibrium, the forward and reverse reaction rates are equal and the concentrations of reactants and products stop changing (though both reactions continue — equilibrium is dynamic, not static). ### The Equilibrium Constant For the general reaction aA + bB <=> cC + dD, the equilibrium constant is: Kc = ([C]^c [D]^d) / ([A]^a [B]^b) where each concentration is the equilibrium value. Pure solids and pure liquids are omitted (their activity is 1). - **Kc** uses molar concentrations. - **Kp** uses partial pressures (for gases): Kp = Kc (RT)^(delta-n), where delta-n = (moles gas products) - (moles gas reactants), R = 0.08206 L-atm/mol-K. - **K >> 1:** products favored. **K << 1:** reactants favored. **K near 1:** appreciable amounts of both. **Reaction quotient Q.** Same expression as K, but with current (non-equilibrium) concentrations. Comparing Q to K pre...