Balancing Equations Flashcards
(8 cards)
Kinetic‑Molecular Theory and Condensed Phases
The kinetic‑molecular theory states that particles are in continuous motion and that the balance between kinetic energy and intermolecular forces dictates the state of matter. In liquids, kinetic energy allows particles to slide past one another yet remain close because attractions still dominate, explaining fluidity and high density. In solids, kinetic energy is too low to overcome these attractions, so particles merely vibrate about fixed lattice positions, giving rigidity.
Chemical Equilibrium
Chemical equilibrium is reached when the forward and reverse reaction rates become equal in a reversible process. At equilibrium, macroscopic concentrations of reactants and products remain constant although molecules continue to interconvert. It is therefore a dynamic, not static, balance.
Endpoint, Equivalence Point, Halfway Point
The equivalence point is the exact volume where moles of titrant equal moles of analyte according to the balanced equation. The endpoint is the observable signal—usually an indicator colour shift—chosen to coincide as closely as possible with that equivalence. In a weak‑acid titration, the halfway point comes when half the acid has been neutralised; there [HA]=[A⁻] and pH=pKₐ.
Oxidation‑Number Changes
When an atom is oxidised its oxidation number increases, signalling that it has lost electron density. Conversely, reduction lowers the oxidation number as the atom gains electron density. Tracking these integer changes helps identify electron flow and balance redox equations.
Anode, Cathode, Salt Bridge Functions
In a voltaic cell the anode is the electrode where oxidation occurs and electrons depart into the circuit; it is labelled negative. The cathode hosts the reduction half‑reaction and receives those electrons, making it positive. The salt bridge completes the circuit internally by allowing inert ions to migrate and balance charge, preventing solution build‑up that would otherwise stop the reaction.
Calculating K₍eq₎
Write the balanced chemical equation, then form the ratio of product activities over reactant activities, each raised to their stoichiometric coefficient. Substitute equilibrium concentrations or partial pressures and perform the arithmetic. Pure solids and liquids drop out because their activities are defined as one.
Concentration from Titration Data
Multiply the titrant molarity by the volume delivered to obtain moles of titrant, convert to moles of analyte using the balanced equation, then divide by the analyte’s volume. Careful unit conversions (mL to L) and stoichiometric ratios are the keys. The result is the unknown molarity of the analyte.
Balancing Redox Reactions
Split the equation into two half‑reactions, balance atoms other than O and H, add H₂O to balance O, H⁺ to balance H, and electrons to balance charge. Equalise electron numbers between halves, add the halves, and cancel common terms. In basic solution, neutralise any H⁺ with OH⁻ to form water.
