NY Regents Chemistry flashcards

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

Significant figures in multiplication

Round the product or quotient to the same number of significant figures as the measurement with the fewest significant figures. For addition and subtraction, round to the fewest decimal places instead.

Density as conversion factor

Density equals mass divided by volume and is intensive, so it does not change with sample size. Use it to convert a given mass to volume or a volume to mass.

Percent error formula

Percent error equals the absolute value of accepted minus measured, divided by accepted, times 100. It compares an experimental result with the accepted value.

Kelvin conversion

Kelvin equals degrees Celsius plus 273. A temperature difference of one kelvin equals one degree Celsius, so differences convert without adding 273.

q = mc delta T

Heat gained or lost equals mass times specific heat capacity times temperature change. A positive q means the system absorbed heat; a negative q means it released heat.

Separating mixtures

Filtration uses particle size, distillation uses boiling point, chromatography uses differing attraction to phases, and evaporation uses volatility. All are physical separations that keep composition unchanged.

Mass number and neutrons

Mass number equals protons plus neutrons, while atomic number equals protons. Neutrons therefore equal mass number minus atomic number, and isotopes differ only in neutron count.

Average atomic mass

The weighted average of isotopic masses, each multiplied by its fractional abundance. Because it is a weighted average of isotopes, it is usually not a whole number.

Excited state electrons

An electron configuration with an electron promoted to a higher sublevel than the ground-state filling order predicts. The electron emits a photon of characteristic energy when it falls back.

Atomic radius trend

Atomic radius decreases across a period because added protons pull the same shell inward, and increases down a group because new shells are added.

First ionization energy trend

The energy needed to remove the outermost electron increases across a period and decreases down a group, since outer electrons are held more weakly as distance from the nucleus grows.

Ion formation

Metals lose electrons to form positively charged cations, nonmetals gain electrons to form negatively charged anions, and noble gases have full valence shells so they rarely form ions.

Ionic bond properties

Electron transfer between metal and nonmetal creates a lattice of cations and anions. The strong attractions give high melting points and conduct electricity when molten or dissolved.

Polar versus nonpolar molecule

A polar bond shares electrons unequally. A molecule is polar only if its bond dipoles do not cancel, so symmetric shapes such as carbon dioxide and methane are nonpolar.

VSEPR shapes

Electron domains repel to maximize separation: two domains are linear, three trigonal planar, four tetrahedral. Lone pairs compress bond angles below the ideal values.

Intermolecular force strength order

Hydrogen bonding, which requires hydrogen bonded to nitrogen, oxygen, or fluorine, is strongest, then dipole-dipole, then London dispersion. All are weaker than covalent or ionic bonds.

Hydrogen bonding effect

Hydrogen bonds between molecules raise boiling point, surface tension, and heat capacity. This is why water boils far above hydrogen sulfide despite its lower molar mass.

Balancing equations rule

Change coefficients only, never subscripts, so each element has equal atoms on both sides. In ionic equations, total charge must also balance.

Molar volume at STP

At standard temperature and pressure, one mole of any ideal gas occupies 22.4 liters. Moles of gas therefore equal volume divided by 22.4 liters.

Limiting reactant

The reactant consumed first, found by comparing available moles with the mole ratio. It determines the maximum product; the other reactant is in excess.

Percent yield

Actual yield divided by theoretical yield, times 100. Theoretical yield comes from stoichiometry using the limiting reactant; actual yield is measured experimentally.

Solubility rules

Most nitrate, sodium, potassium, and ammonium salts dissolve. Most chlorides dissolve except those of silver, lead, and mercury; most carbonates and hydroxides are insoluble.

Net ionic equation

An equation showing only the species that actually react, with spectator ions removed. A precipitate, gas, or weak electrolyte must form for double replacement to occur.

Collision theory

Particles must collide with enough energy and proper orientation to react. Raising temperature, concentration, or surface area, or adding a catalyst, increases the reaction rate.

Catalyst effect

A catalyst lowers activation energy by an alternate pathway without being consumed. It speeds both forward and reverse reactions equally, so equilibrium position and enthalpy change are unchanged.

Le Chatelier's principle

A stress on a system at equilibrium shifts it to counteract that stress. Adding reactant shifts right, adding product shifts left, and heating shifts an endothermic reaction right.

Dynamic equilibrium

Forward and reverse reaction rates are equal and concentrations stay constant, though both reactions continue. The equilibrium constant K is the ratio of product to reactant concentrations.

Hess's law

The enthalpy change of an overall reaction equals the sum of the enthalpy changes of its individual steps, so delta H can be calculated from known reactions.

Hydrocarbon formulas

Alkanes have only single bonds with formula C_nH_2n+2, alkenes have one double bond with C_nH_2n, and alkynes have one triple bond with C_nH_2n-2.

Organic functional groups

Alcohols contain -OH, organic acids contain -COOH, aldehydes contain -CHO, ketones contain C=O within the chain, esters contain -COO-, and amines contain -NH2.

Alpha and beta decay

Alpha decay emits a helium nucleus, lowering mass number by 4 and atomic number by 2. Beta decay turns a neutron into a proton, raising atomic number by 1 with mass number unchanged.

Half-life calculation

After n half-lives, the fraction of radioactive nuclei remaining is one-half raised to the nth power. Multiply the original amount by that fraction to find what remains.