Praxis Chemistry 5245 flashcards
Praxis Chemistry 5245 · Build recall with a focused review session.
33 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Atomic number
- The number of protons in an atom's nucleus; it uniquely identifies the element and equals the electron count in a neutral atom.
- Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons, giving different mass numbers and slightly different atomic masses.
- Aufbau principle
- Electrons fill the lowest-energy orbitals first; the order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, and so on.
- Hund's rule
- Within a set of degenerate orbitals, electrons occupy separate orbitals with parallel spins before any pairing occurs, minimizing electron repulsion.
- Mole
- The amount of substance containing 6.022×10^23 representative particles (Avogadro's number); the bridge between particle counts and measurable mass.
- Limiting reactant
- The reactant that is completely consumed first, determined by comparing product yields from each reactant; it sets the maximum theoretical yield.
- Percent yield
- The actual yield divided by the theoretical yield, multiplied by 100; it measures the efficiency of a reaction.
- Oxidation
- Loss of electrons by a species, accompanied by an increase in oxidation number; it is always paired with reduction in a redox reaction.
- Enthalpy of reaction
- The heat exchanged at constant pressure, computed as the sum of product formation enthalpies minus the sum of reactant formation enthalpies.
- Hess's law
- The total enthalpy change of a reaction is independent of the pathway; reversing a step flips the sign of its enthalpy change.
- Calorimetry
- The measurement of heat exchange using q = mcΔT for a solution or q = CΔT for a calorimeter, allowing determination of reaction enthalpy.
- Electronegativity
- The tendency of an atom to attract shared electrons in a bond; large differences between atoms produce ionic rather than covalent bonding.
- VSEPR theory
- Electron domains around a central atom arrange to minimize repulsion, determining molecular geometry from the number of bonding and lone pairs.
- Hybridization
- The mixing of atomic orbitals to form equivalent bonding orbitals; steric number 2, 3, and 4 correspond to sp, sp2, and sp3.
- Hydrogen bonding
- A strong dipole attraction between H bonded to N, O, or F and a lone pair on a nearby electronegative atom; raises boiling points.
- London dispersion forces
- Weak, temporary attractions from instantaneous dipoles; they strengthen with larger electron clouds and are present in all molecules.
- Molecular polarity
- A net dipole resulting from polar bonds arranged asymmetrically; symmetric geometries such as linear CO2 or tetrahedral CCl4 cancel to nonpolar.
- pH
- The negative base-10 logarithm of hydrogen ion concentration; values below 7 are acidic and above 7 are basic at 25 °C.
- Brønsted–Lowry acid
- A proton (H+) donor; its conjugate base is what remains after it loses a proton, forming a conjugate acid–base pair.
- Ka
- The acid dissociation constant for a weak acid; a larger Ka indicates a stronger acid and greater extent of ionization.
- Buffer
- A solution of a weak acid and its conjugate base that resists pH change; capacity is greatest when pH equals pKa.
- Molarity
- Moles of solute divided by liters of solution; dilution follows M1V1 = M2V2 because solute moles stay constant.
- Titration equivalence point
- The point where moles of added titrant equal the stoichiometric moles needed to react with the analyte, often detected by an indicator color change.
- Rate law
- An equation relating reaction rate to reactant concentrations raised to experimentally determined orders, with k as the rate constant.
- Activation energy
- The minimum energy reactants need to form the transition state; catalysts lower it, increasing the fraction of successful collisions.
- Equilibrium constant
- The ratio of product concentrations to reactant concentrations, each raised to its coefficient; pure solids and liquids are excluded.
- Le Châtelier's principle
- When a stress such as concentration, pressure, or temperature change is applied to a system at equilibrium, it shifts to partially offset the stress.
- Reaction quotient Q
- The same ratio as K but using current concentrations; Q below K drives the reaction forward, Q above K drives it in reverse.
- Significant figures
- Digits that convey measurement precision; rules govern counting them and rounding results of multiplication, division, addition, and subtraction.
- Accuracy versus precision
- Accuracy describes closeness to the accepted value; precision describes how closely repeated measurements agree with one another.
- Adding acid to water
- A safety rule: pour acid slowly into water with stirring, never water into acid, to control the heat released by dilution.
- Atom economy
- The molar mass of the desired product divided by the total molar mass of all reactants, times 100; a green-chemistry efficiency metric.
- Half-life
- The time for half of a radioactive sample to decay; for first-order kinetics it equals 0.693 divided by the rate constant.