NYSTCE Chemistry flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Independent variable

The factor the experimenter deliberately changes or manipulates. Its effect on the measured dependent variable is what the investigation tests, while all other conditions are held constant.

Accuracy versus precision

Accuracy measures how close a result is to the accepted true value. Precision measures how closely repeated trials agree with one another, regardless of whether they are correct.

Significant figure rules

All nonzero digits count, as do zeros between them and trailing zeros after a decimal point. Leading zeros never count. Multiplication rounds to least significant figures; addition rounds to least decimal places.

Intensive versus extensive property

Intensive properties such as density, boiling point, and color do not depend on sample size. Extensive properties such as mass, volume, and heat capacity change with the amount of material present.

Law of definite proportions

A given compound always contains the same elements in the same fixed ratio by mass, regardless of the sample's source or how it was prepared.

Limiting reactant

The reactant that is completely consumed first and therefore determines the maximum amount of product formed. Any other reactant remains in excess after the reaction stops.

Molarity

Moles of solute dissolved per liter of solution, abbreviated M. Dilution problems use M₁V₁ = M₂V₂ because the moles of solute stay constant when solvent is added.

Net ionic equation

A balanced equation showing only the ions and molecules that actually change during a reaction. Spectator ions, unchanged on both sides, are omitted, and both atoms and charge balance.

Hund's rule

Within a set of degenerate orbitals, electrons occupy separate orbitals with parallel spins before any pairing occurs, minimizing electron–electron repulsion and lowering overall energy.

Ionization energy trend

Ionization energy increases across a period as nuclear charge grows and atomic radius shrinks, and decreases down a group as outer electrons sit farther from the nucleus.

Average atomic mass

The weighted average of the masses of an element's naturally occurring isotopes, each multiplied by its fractional abundance and summed; this value appears on the periodic table.

VSEPR theory

Electron domains around a central atom repel and spread as far apart as possible. Two domains give linear, three trigonal planar, four tetrahedral, five trigonal bipyramidal, and six octahedral shapes.

Hydrogen bonding

A strong intermolecular attraction between a hydrogen atom covalently bonded to nitrogen, oxygen, or fluorine and a lone pair on a nearby electronegative atom. It raises boiling points.

Polar versus nonpolar molecule

Polar bonds combined with asymmetric geometry produce a net dipole and a polar molecule. Symmetric geometry cancels individual bond dipoles, leaving a nonpolar molecule such as carbon dioxide.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature. Use R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K), and always convert temperature to kelvin.

Graham's law of effusion

The rate at which a gas effuses is inversely proportional to the square root of its molar mass, so lighter gases escape faster through a small opening at constant temperature.

Boiling point definition

The temperature at which a liquid's vapor pressure equals the external pressure applied to it. The normal boiling point is measured at exactly one atmosphere.

Hess's law

The enthalpy change of an overall reaction equals the sum of the enthalpy changes of its individual steps, because enthalpy is a state function and the path does not matter.

Gibbs free energy

ΔG = ΔH − TΔS determines spontaneity. A negative ΔG means the process is spontaneous, positive means nonspontaneous, and zero means the system is at equilibrium.

Calorimetry equation

q = mcΔT calculates heat absorbed or released, where m is mass, c is specific heat capacity, and ΔT is the temperature change. At constant pressure, q equals ΔH.

Le Chatelier's principle

When a stress such as a concentration change, pressure change, or temperature change is applied to a system at equilibrium, the system shifts to counteract that stress.

Henderson–Hasselbalch equation

pH = pKa + log([conjugate base]/[weak acid]) predicts the pH of a buffer solution and shows that pH equals pKa when the acid and base concentrations are equal.

pH scale

pH = −log[H⁺]. At 25 °C, pH below 7 is acidic, pH equal to 7 is neutral, and pH above 7 is basic; pH plus pOH equals 14.

Oxidation and reduction

Oxidation is loss of electrons and an increase in oxidation number. Reduction is gain of electrons and a decrease in oxidation number; the two always occur together.

Standard cell potential

E°cell = E°cathode − E°anode, calculated from standard reduction potentials. A positive value indicates a spontaneous galvanic reaction; a negative value requires an external power source.

Anode and cathode

Oxidation always occurs at the anode, and reduction always occurs at the cathode. In a galvanic cell, electrons flow through the external circuit from anode to cathode.

Peptide bond

A covalent amide linkage formed between the carboxyl group of one amino acid and the amino group of another, releasing water and building the polypeptide chain of a protein.

Functional group

A specific group of atoms within an organic molecule, such as hydroxyl, carboxyl, amino, or ester, that determines the molecule's characteristic chemical reactivity and properties.

Alpha decay

Radioactive emission of a helium-4 nucleus. The daughter nucleus has a mass number reduced by four and an atomic number reduced by two compared with the parent.

Half-life

The time required for half of a radioactive sample to decay. After n half-lives, the fraction remaining equals one-half raised to the nth power.

Beta-minus decay

A neutron converts into a proton, emitting an electron and an antineutrino. The mass number stays the same while the atomic number increases by one.

Adding acid to water

Always add concentrated acid slowly to water with stirring, never water to acid. The dilution releases heat, and this order keeps the mixture from boiling and splattering.

Safety Data Sheet

A standardized document for each chemical listing hazard identification, first-aid measures, handling and storage precautions, and spill-response information required in school laboratories.