GACE Chemistry (712) flashcards
GACE Chemistry (712) · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Accuracy versus precision
- Accuracy measures how close a result is to the accepted value; precision measures how closely repeated measurements agree with one another. Systematic error harms accuracy, while random error mainly harms precision.
- Hypothesis
- A testable, falsifiable proposed explanation for an observation. It must predict measurable outcomes so that a controlled experiment can support or refute it rather than merely describe.
- Significant figure rule
- For multiplication and division, round the answer to the fewest significant figures in any factor. For addition and subtraction, round to the fewest decimal places among the terms.
- Percent error
- Absolute difference between measured and accepted value, divided by the accepted value, multiplied by 100. A small percent error indicates the measurement is close to the true value.
- Isotope
- Atoms of the same element with identical proton number but different neutron number, giving different mass numbers. Isotopes share chemical behavior but differ in mass and nuclear stability.
- Hund's rule
- Within a subshell, electrons occupy separate orbitals with parallel spins before any orbital receives a second electron. This arrangement minimizes electron repulsion and maximizes total spin.
- Beta-minus decay
- A neutron converts to a proton, emitting an electron and an antineutrino. The mass number stays the same while the atomic number increases by one, forming a new element.
- Half-life calculation
- The remaining fraction equals one-half raised to the number of elapsed half-lives. If two half-lives pass, one quarter of the original radioactive nuclei remain undecayed.
- Ionization energy trend
- Ionization energy increases across a period as effective nuclear charge rises, and decreases down a group as outer electrons sit farther from the nucleus and are shielded.
- VSEPR theory
- Electron domains around a central atom repel and spread as far apart as possible. Lone pairs occupy more space than bonding pairs, compressing bond angles below ideal values.
- Hydrogen bonding
- A strong dipole attraction between hydrogen bonded to nitrogen, oxygen, or fluorine and a lone pair on another electronegative atom. It raises boiling points and shapes proteins and water.
- Polar versus nonpolar molecule
- Polar bonds plus asymmetric geometry yield a net molecular dipole. Symmetric arrangements such as linear carbon dioxide or tetrahedral carbon tetrachloride cancel individual bond dipoles.
- Hybridization from steric number
- Steric number two gives sp, three gives sp-squared, and four gives sp-cubed. The number counts sigma bonds plus lone pairs on the central atom.
- Formal charge
- Valence electrons minus nonbonding electrons minus half the bonding electrons. The Lewis structure with formal charges closest to zero is generally the most stable resonance contributor.
- Limiting reactant
- The reactant consumed first, determined by converting each reactant amount to product moles and choosing the smallest. It caps theoretical yield; other reactants remain in excess.
- Hess's law
- The enthalpy change of an overall reaction equals the sum of enthalpy changes of any sequence of steps that adds to it. This allows indirect calculation using formation enthalpies.
- Gibbs free energy
- Delta G equals enthalpy change minus temperature times entropy change. A negative value indicates a spontaneous process at that temperature; zero indicates equilibrium.
- Percent yield
- Actual product mass divided by theoretical product mass, multiplied by 100. Theoretical yield comes from stoichiometry using the limiting reactant; losses reduce actual yield.
- Molarity
- Moles of solute divided by liters of solution. Because volume changes with temperature, molarity is temperature dependent, unlike molality, which uses kilograms of solvent.
- Colligative properties
- Properties depending on the number of dissolved particles rather than identity: vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. The van't Hoff factor counts particles.
- Le Chatelier's principle
- A system at equilibrium shifts to partially offset a stress such as concentration change, pressure change, or temperature change. Heating favors the endothermic direction of the reaction.
- Activation energy
- The minimum energy colliding molecules need to form products. Catalysts lower it, increasing the rate constant without changing enthalpy change or the equilibrium constant.
- Equilibrium constant expression
- Products raised to their coefficients divided by reactants raised to theirs, using equilibrium concentrations. Pure solids and liquids are omitted because their activity is one.
- Dilution equation
- Initial molarity times initial volume equals final molarity times final volume. Adding solvent increases volume and lowers concentration while leaving solute moles unchanged.
- Functional group
- A specific atom grouping that determines a molecule's characteristic reactions and properties, such as hydroxyl in alcohols, carboxyl in acids, or amide in proteins.
- Esterification
- A carboxylic acid reacts with an alcohol, typically with acid catalysis, producing an ester and water. The reaction is a condensation and is reversible through hydrolysis.
- Enantiomers
- Stereoisomers that are non-superimposable mirror images, arising from a carbon bonded to four different groups. They rotate plane-polarized light in opposite directions.
- Peptide bond
- A covalent amide linkage formed by condensation between the carboxyl group of one amino acid and the amino group of another, releasing water and building polypeptide chains.
- Addition polymerization
- Alkene monomers join through their double bonds to form a long chain without producing a small byproduct. Polyethylene and polystyrene form this way.
- Enzyme specificity
- An enzyme's active site binds only particular substrates, lowering activation energy for their conversion. Activity depends strongly on temperature, pH, and cofactors.
- Eutrophication
- Excess nitrates and phosphates in water trigger algal blooms; decomposition then depletes dissolved oxygen, harming fish and other aquatic organisms.
- Greenhouse effect
- Certain atmospheric gases absorb and re-emit infrared radiation, warming the surface. Carbon dioxide, methane, nitrous oxide, and water vapor are the principal contributors.