# Chemistry 12 reference sheet

## Kinetics and energy
- Average reaction rate: r=-Delta[R]/Delta t=Delta[P]/Delta t after accounting for the chosen stoichiometric convention.
- Activation energy: E_a=E_TS-E_R.
- Reaction enthalpy: Delta H=H_P-H_R.
- Catalysts lower activation barriers through an alternative pathway; they do not change Delta H or K at fixed temperature.

## Equilibrium
- For aA+bBrightleftharpoons cC+dD, K_c=[C]^c[D]^d/([A]^a[B]^b) for species included in the concentration expression.
- Omit pure solids and pure liquids from concentration-form equilibrium expressions.
- Compare Q with K: Q<K net forward, Q>K net reverse, Q=K equilibrium.
- ICE tables connect initial, stoichiometric change, and equilibrium concentrations.

## Solubility
- K_sp follows dissolution stoichiometry; translate molar solubility s into each ion concentration first.
- Compare Q_sp with K_sp to predict precipitation.
- At the precipitation threshold, Q_sp=K_sp.

## Acid–base systems (25 °C classroom model unless otherwise stated)
- K_w=[H_3O^+][OH^-]=1.0times10^-14.
- pH=-log[H_3O^+], pOH=-log[OH^-], pH+pOH=14.00.
- K_a=[H_3O^+][A^-]/[HA] and K_b=[BH^+][OH^-]/[B].
- For a conjugate pair at the same temperature, K_aK_b=K_w.
- Titration equivalence follows balanced stoichiometry; endpoint is the experimental indicator/instrument signal.
- Buffer calculations can be obtained directly from the K_a or K_b expression after any strong-acid/base stoichiometric reaction.

## Redox and electrochemistry
- Oxidation = electron loss; reduction = electron gain.
- Balance atoms and charge in half-reactions before combining; electrons cancel in the net reaction.
- E^circ_cell=E^circ_cathode-E^circ_anode using tabulated reduction potentials.
- Do not multiply electrode potentials by stoichiometric coefficients.
- Electron coefficients connect cell reaction extent to electrode mass change.

## Quality checks
Preserve raw data; carry units and guard digits; report justified significant figures; check atom/charge conservation; state temperature/standard-state assumptions; distinguish thermodynamic direction from reaction rate; evaluate uncertainty, controls, source quality, safety, and model domain.
