LC Chemistry flashcards
LC Chemistry · Build recall with a focused review session.
36 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 the nucleus of an atom; it defines the element and equals the number of electrons in a neutral atom.
- Isotopes
- Atoms of the same element with the same proton number but different neutron numbers, so they have different mass numbers and slightly different physical properties.
- First ionisation energy
- The energy needed to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Aufbau principle
- Electrons occupy the lowest available energy orbital first, filling in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d and so on.
- Ionic bond
- The electrostatic attraction between oppositely charged ions formed by complete transfer of electrons from a metal atom to a non-metal atom.
- Hydrogen bonding
- A strong intermolecular attraction between a hydrogen atom bonded to N, O or F and a lone pair on a nearby electronegative atom.
- VSEPR theory
- Electron pairs around a central atom repel each other and arrange as far apart as possible, determining the molecular shape and bond angles.
- Sigma bond
- A covalent bond formed by end-on overlap of orbitals, with electron density concentrated along the line joining the two nuclei; rotation is possible.
- Limiting reagent
- The reactant that is completely consumed first in a reaction; it determines the maximum amount of product that can be formed.
- Percentage yield
- The actual mass of product obtained expressed as a percentage of the theoretical maximum mass calculated from the balanced equation and limiting reagent.
- Molar volume of gas
- The volume occupied by one mole of any gas under specified conditions: about 24 dm³ at room temperature and pressure, 22.7 dm³ at STP.
- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound, obtained by dividing mole ratios by the smallest value.
- Spectator ions
- Ions present in a reaction mixture that are unchanged on both sides of the equation and are therefore omitted from the net ionic equation.
- Oxidation number
- A number assigned to an element in a compound representing the charge it would carry if all bonds were treated as ionic; oxidation is an increase.
- Precipitation reaction
- A reaction in which two soluble salts in solution exchange ions to form an insoluble solid product that separates from the mixture.
- Equivalence point
- The point in a titration where the amount of titrant added exactly reacts with the amount of substance in the flask, according to the stoichiometry.
- Buffer solution
- A solution of a weak acid and its conjugate base that resists significant pH change when small amounts of acid or alkali are added.
- pH definition
- The negative logarithm to base ten of the hydrogen ion concentration in mol dm⁻³; a change of one pH unit means a tenfold concentration change.
- Ideal gas law
- The relationship pV = nRT linking pressure, volume, amount of gas and absolute temperature; R is the universal gas constant 8.314 J K⁻¹ mol⁻¹.
- Dalton's law
- The total pressure exerted by a mixture of non-reacting gases equals the sum of the partial pressures that each gas would exert alone.
- Absolute temperature
- Temperature measured on the kelvin scale, obtained by adding 273 to the Celsius value; it must be used in all gas law calculations.
- Colligative properties
- Properties such as boiling point elevation, freezing point depression and osmotic pressure that depend on the number of dissolved particles, not their identity.
- Molality
- The amount of solute in moles dissolved in one kilogram of solvent; unlike molarity it does not change with temperature.
- Osmotic pressure
- The pressure needed to prevent net movement of solvent across a semipermeable membrane into a solution; given by π = iMRT.
- Hess's law
- The total enthalpy change of a reaction is the same regardless of the route taken, allowing enthalpy changes to be calculated by summing steps.
- Activation energy
- The minimum kinetic energy that colliding particles must possess for a reaction to occur; a catalyst lowers it without changing the enthalpy change.
- Dynamic equilibrium
- A state in a reversible reaction where the forward and reverse rates are equal, so concentrations stay constant while both reactions continue.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts to oppose the change.
- Equilibrium constant Kc
- The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric power, at equilibrium; it depends only on temperature.
- Electrophilic addition
- A reaction of an alkene in which an electron-rich double bond attacks an electrophile, forming a carbocation intermediate that is then attacked by a nucleophile.
- Esterification
- The reversible reaction of a carboxylic acid with an alcohol, catalysed by concentrated sulfuric acid, producing an ester and water.
- Electrolysis
- The decomposition of a compound by passing a direct electric current through it in molten or aqueous form, with oxidation at the anode and reduction at the cathode.
- Standard electrode potential
- The potential of a half-cell measured against the standard hydrogen electrode under standard conditions of 298 K, 1 mol dm⁻³ and 100 kPa.
- Faraday constant
- The electric charge carried by one mole of electrons, approximately 96 500 coulombs per mole; used to relate charge passed to moles of substance electrolysed.
- Concordant titres
- Repeat titration volumes that agree closely, usually within 0.10 cm³ of each other, allowing a reliable mean to be calculated.
- Weighing by difference
- A technique where the mass of substance transferred is found by subtracting the final container mass from the initial mass, reducing transfer error.