FTCE Chemistry 6-12 flashcards

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

Significant figures rule

In multiplication and division, the result keeps the least number of significant figures found in any factor. In addition and subtraction, keep the least number of decimal places.

Accuracy versus precision

Accuracy measures how close a result is to the true value; precision measures how closely repeated measurements agree with each other. Systematic error harms accuracy; random error harms precision.

Percent error formula

Percent error equals the absolute difference between experimental and accepted value, divided by the accepted value, then multiplied by 100. It quantifies measurement deviation.

Dimensional analysis

A problem-solving method that multiplies a quantity by conversion factors equal to one, arranging units so unwanted units cancel and only the desired unit remains.

Controlled experiment

An investigation that deliberately changes one independent variable while holding all other conditions constant, then measures the resulting dependent variable against a control group.

Density as derived quantity

Density equals mass divided by volume. Because it is an intensive property, it can help identify an unknown substance and assess sample purity.

Homogeneous versus heterogeneous mixture

A homogeneous mixture has uniform composition throughout, like salt water. A heterogeneous mixture has visibly uneven composition, like sand and iron filings, and separates physically.

Physical versus chemical change

A physical change alters state or form without changing composition. A chemical change produces new substances, often signaled by gas, precipitate, color change, heat, or light.

Atomic number and mass number

Atomic number equals the number of protons and identifies the element. Mass number equals protons plus neutrons. Isotopes of an element share atomic number but differ in neutrons.

Periodic trend summary

Atomic radius decreases left to right across a period and increases down a group. Ionization energy and electronegativity increase left to right and upward within a group.

Mole and Avogadro's number

One mole contains 6.022 times ten to the twenty-third particles and equals the molar mass in grams. Molarity equals moles of solute divided by liters of solution.

First law of thermodynamics

Energy cannot be created or destroyed, only converted between forms. For a system, the change in internal energy equals heat added plus work done on the system.

Hess's law

The enthalpy change of an overall reaction equals the sum of enthalpy changes for any sequence of steps that add to it. Reversing a step reverses the sign of its enthalpy.

Calorimetry equation

Heat transferred equals mass times specific heat times temperature change, written q = mcΔT. For a bomb calorimeter, q equals heat capacity times temperature change instead.

Gibbs free energy criterion

Change in Gibbs free energy equals enthalpy change minus temperature times entropy change. A negative value means the process is spontaneous; zero means the system is at equilibrium.

Catalyst effect

A catalyst lowers activation energy by providing an alternate pathway, speeding both forward and reverse rates. It does not change enthalpy change or the equilibrium position.

Le Chatelier's principle

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

Equilibrium constant expression

For a balanced reversible reaction, K equals the product concentrations each raised to their coefficients, divided by reactant concentrations raised to their coefficients. Values above one favor products.

Ionic versus covalent bonding

Ionic bonding transfers electrons between metal and nonmetal, giving high melting points and conductivity when molten. Covalent bonding shares electrons between nonmetals.

Electronegativity difference guideline

A difference above about 1.7 suggests mostly ionic character; between 0.4 and 1.7 suggests polar covalent; below 0.4 suggests essentially nonpolar covalent bonding.

VSEPR theory

Electron pairs around a central atom repel and arrange as far apart as possible. Lone pairs occupy more space than bonding pairs, compressing bond angles below ideal values.

Hybridization and geometry

sp hybridization gives linear geometry with 180-degree angles; sp2 gives trigonal planar with 120 degrees; sp3 gives tetrahedral with about 109.5 degrees.

Hydrogen bonding requirement

Hydrogen bonding occurs when hydrogen is covalently bonded to nitrogen, oxygen, or fluorine and interacts with a lone pair on another electronegative atom. It raises boiling points.

Intermolecular force strength order

From strongest to weakest: ion-dipole, hydrogen bonding, dipole-dipole, and London dispersion forces. Stronger intermolecular forces generally produce higher boiling points and surface tension.

Molecular polarity test

A molecule is polar when its bond dipoles do not cancel through symmetry. Carbon dioxide is nonpolar because dipoles cancel; water is polar because they do not.

Metallic bonding model

Metal cations sit in a sea of delocalized valence electrons. Mobile electrons explain electrical and thermal conductivity, while layer sliding explains malleability and ductility.

Five reaction types

Synthesis combines reactants; decomposition splits one reactant; single replacement swaps one element; double replacement exchanges ions; combustion burns fuel with oxygen to make carbon dioxide and water.

Stoichiometry conversion path

Convert grams of known to moles using molar mass, convert moles of known to moles of unknown using the mole ratio from coefficients, then convert to grams using molar mass.

Limiting reactant

The reactant that is completely consumed first and therefore determines the maximum product formed. Other reactants are in excess and remain after the reaction stops.

Percent yield

Percent yield equals actual product mass divided by theoretical product mass, multiplied by 100. Theoretical mass is calculated from the limiting reactant using stoichiometry.

Dilution equation

Molarity times volume before dilution equals molarity times volume after dilution, written M1V1 = M2V2. Moles of solute stay constant when solvent is added.

Net ionic equation

An equation showing only the species that actually react. Spectator ions appearing unchanged on both sides are canceled; an insoluble product appears as a precipitate.