Chemistry

Standard conditions for cell potential stuff

• An ion concentration of 1.00 mol dm^-3

• A temperature of 298 K

• A pressure of 1 atm

Standard eletrode potential def

• Potential difference when a half-cell is connected to a standard hydrogen electrode under standard conditions.

Standard cell potential def

• Potential difference between 2 half-cells under standard conditions of 1 atm, 298k, and all solutions at 1.00 mol/dm³

Lattice energy

• Enthalpy change when 1 mol of an ionic compound is formed from its gaseous ions under standard conditions

• Exothermic

Atomisation

• Enthalpy change when 1 mol of gaseous atoms is formed from its element under standard conditions

• Endothermic

Electron affinity

• Enthalpy change when 1 mol of electrons is added to 1 mol of gaseous atoms to form 1 mol of gaseous negative ions under standard conditions

• First exothermic, then endo

Enthalpy of solution

• Enthalpy change when 1 mol of an ionic substance dissolves in sufficient H2O forming a very dilute solution under standard conditions

• can be exothermic or endothermic

Enthalpy of hydration

• Enthalpy change when 1 mol of specified gaseous ion dissolves in sufficient water forming a very dilute solution under standard conditions.

• Exothermic

• Hsol - Hlattice dissociation = H hydration

Entropy

• Number of possible arrangements for the particles and its energy in a given system.

Rate of reaction

• Change in concentration of a reactant or product per unit time

Rate equation

• K only affected by temperature

• Order only found experimentally

Half life

• Time taken for concentration of limiting reactant to half

• 0.693/k

Order of reaction from half life

• Zero order = Half lives decrease, takes less time for reactant conc to half

• First order = half life constant

• Second order = half life increases with time, takes more time for reactant conc to half

Mode of action of heterogeneous catalysts

• Adsorption of reactants on catalyst surface

• Reactant physically adsorbed onto surface by weak forces

• Chemically adsorbed by stronger bonds

• Causes bonds to weaken in atoms of reactants

• Desorption, bonds between products and catalyst weaken, products break away.

Iron in haber process

• N & H diffuse onto iron surface

• Adsorbed onto iron surface due to bonds between iron and reactants

• Those bonds weaken N-N & H-H bonds

• N and H reacnt = NH3

• Desorption, NH3 & iron bonds break and NH3 diffuse away

Catalytic converters

• Removes oxides of nitrogen and CO, NOx → N2, CO → CO2

• Honeycomb, small beads, platnium palladium rhodium

• Adsorption of NOx & CO

• Weakening of NO and CO bonds

• Bonds form between adjacent N-N

• CO and O form CO2

• CO2 and N2 desorption, diffuse away.

Homogeneous, peroxydisulfate - iodine reaction

• S2O8 + 2I- → 2SO4(2-) + I2

• Negative reactants = repulsive = lots of energy

• Fe3+ reduced to Fe2+ by I-

• Fe2+ oxidised back to Fe3+ by S2O8(2-)

• No repulsive forces by reacting wt +ve Fe ion, Ea lowered.

NO2 as catalyst

• SO3 + H2O → H2SO4

• NO2 + SO2 → SO3 + NO

• NO + 1/2 O2 → NO2

Nitrates & Carbonates thermal stability trend

• More thermally stable down group

• Lower charge density = less polarisation = keeps No3/Co3 bond stable/doesnt distort its bonds.

  • Polarisation = drawing electrons towards itself.

Solubility of sulfates and hydroxides

• Solubility of OH- increases down group

• Solubility of SO4(2-) decreases down group

• BaSO4 completely insoluble

Enthalpy of lattice energy

• ΔHlatt decreases down group

• Cations larger down group = more space between +ve and -ve ions

• Weaker attractive forces

• Less energy released when formed from gaseous ions

• ΔHlatt becomes less exothermic
  

Enthalpy of hydration

• Decreases down group 2

• Larger cations = weaker ion dipoles

• Less energy released when gaseous group 2 ions hydrated

• ΔHhyd less exothermic

ΔHsol of hydroxides

• OH- = small

• ΔHlatt falls faster than ΔHhyd

• ΔHsol more exothermic down G2

ΔHsol of SO42-

• SO42- = large ion

• ΔHlatt falls slower than ΔHhyd

• ΔHsol becomes less exothermic down group

• More exothermic ΔHsol = more soluble