Gases Flashcards
(12 cards)
Metals, Nonmetals, and Metalloids
Metals are lustrous, malleable, and good conductors that tend to lose electrons to form cations. Nonmetals are dull, brittle or gaseous, poor conductors, and they prefer to gain or share electrons covalently. Metalloids straddle the metal‑nonmetal boundary and show intermediate, direction‑dependent behaviour; silicon, for example, conducts electricity only under certain conditions.
Properties of Liquids and Solids
Liquids have definite volume but assume the shape of their container, exhibit fluidity, surface tension, and slight compressibility. Solids possess definite shape and volume, are rigid, and compress only negligibly. Both phases are much denser than gases because their particles remain close together.
Changes of State
The six common phase changes are melting, freezing, vaporisation (boiling or evaporation), condensation, sublimation, and deposition. Each process involves energy transfer without altering chemical identity. Melting and vaporisation absorb heat, freezing and condensation release it, and sublimation and deposition bridge solid and gas directly.
Particulate View of Phase Changes
During melting, added energy breaks some intermolecular attractions so particles leave fixed lattice sites and move past one another. Vaporisation supplies enough energy for particles to overcome attractions entirely and disperse as gas; condensation is the reverse, releasing energy and reforming attractions. Sublimation allows surface molecules of a solid to escape directly into the gas when their kinetic energy exceeds all attractions, while deposition traps gaseous particles directly into a solid lattice.
Solubility and Its Controlling Factors
Solubility is the maximum amount of solute that dissolves in a given quantity of solvent at a specified temperature and pressure, yielding a saturated solution. It depends on the relative strengths of solute–solute, solvent–solvent, and solute–solvent interactions, plus temperature, pressure for gases, and sometimes pH. Altering these factors shifts the saturation limit.
Solvation and Its Controlling Factors
Solvation is the process by which solvent molecules attract, surround, and separate solute particles, drawing them into solution. Its rate and extent depend on temperature, agitation, solute surface area, and the compatibility of intermolecular forces between solute and solvent (‘like dissolves like’). In water the special case is hydration, where hydrogen bonding accelerates the process.
Le Châtelier’s Principle
Le Châtelier’s principle states that if a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, the system shifts in the direction that counteracts the disturbance. This shift establishes a new equilibrium consistent with the new conditions. Catalysts do not affect the position, only the rate at which equilibrium is reached.
Standard Cell Potential
The standard cell potential E°₍cell₎ equals the cathode’s standard reduction potential minus the anode’s. It is measured under 1M ion concentrations, 1atm gases, and 25°C. A positive E°₍cell₎ indicates that the redox process is spontaneous under standard conditions.
Entropy, Enthalpy, Gibbs Free Energy
Enthalpy ΔH measures heat released or absorbed at constant pressure, entropy ΔS gauges the dispersal of energy and matter, and Gibbs free energy ΔG combines both as ΔG=ΔH−TΔS. A negative ΔG signals a process that can proceed spontaneously. Thus free energy weighs the enthalpy ‘pay‑off’ against the entropy ‘cost’ (or vice versa) at a given temperature.
Predicting Equilibrium Shifts (LeChâtelier)
Calculate the reaction quotient Q the same way as K₍eq₎ but with current concentrations. If Q<K the system lacks products and will shift right; if Q>K it has excess products and shifts left. Changing pressure, temperature, or concentrations perturbs Q and the system responds to restore equilibrium.
[H₃O⁺] from [OH⁻] and Vice Versa
Because K₍w₎ = [H₃O⁺][OH⁻]=1.0 × 10⁻¹⁴ at 25 °C, dividing that constant by one ion’s concentration immediately yields the other. The product must always satisfy the equilibrium regardless of what else is in solution. Remember to adjust K₍w₎ if the temperature differs appreciably from 25 °C.
Acidic or Basic Solution Identification
If [H₃O⁺] > 1.0 × 10⁻⁷ M (pH < 7) the solution is acidic; if [OH⁻] > 1.0 × 10⁻⁷ M (pOH < 7) it is basic. The same thresholds apply when using pH directly: below 7 acidic, above 7 basic at 25 °C. Neutrality shifts slightly with temperature as K₍w₎ changes.
