Oceans - Topic 8

• what do ionic substances dissolve in: polar solvents - non polar solvents not strong enough to pull ions out of their lattice - electrostatic forces too strong
• what do covalent substances dissolve in: non polar solvents - as im bonds are weak and can ve broken easily
• What are ion-dipole bonds? formed between H20 and dissolved ions with delta charges
• hydration


  process of ions being surrounded by h20 molecules
• hydrated ions: when ions are surrounded by h2o molecules - name of ions
• solvation: same as hydration just with a different solvent e.g ethanol
• ion dipole bonds: strong enough to pull ions from lattice therefore ionic solids dissolve in h20
• Standard lattice enthalpy: The enthalpy change when one mole of ionic lattice is formed from its gaseous ions under standard conditions- always exothermic as bonds are broken and energy is released
• enthalpy change of hydration: when one mole of aqueous ions are formed from gaseous ions - always endothermic as bonds between ions and h20 are made
• enthalpy change of solution: when one mole of ionic substance dissolves in enough solvent to form an infinitely dilute solution
• how to work out enthalpy change of solution: - LE + (HYD CATION AND ANION)
• How to measure enthalpy change of solution: q=mcT and h=q/n
• higher charge density - LE: better attracting each other in ionic lattices - stronger ionic bonds - more energy released when bonds are made - more exothermic lattice enthalpy
• higher charge density - hydration: better at attracting water molecules with lower charge densities - stronger im bonds - more energy released when breaking bonds - more exothermic enthalpy
• entropy


  a measure of the disorder of a system
• factors affecting entropy: physical state , amount of energy , number of particles
• how does physical state affect entropy: solid to gas - more ways to arrange particles - more disorder more positive entropy
• hows does energy affect entropy: energy in quanta the more energy in quanta a substance has the more ways they can be arranged - greater entropy
• how does number of particles affect entropy: more no of moles greater entropy - more ways energy can be rearranged
• how to calculate total entropy change: entropy change of system + entropy change of surroundings
• entropy change of system


  products - reactants
• entropy change of surroundings: - enthalpy change / temp (K)
• feasible


  total entropy change greater than zero
• for a reaction to occur: total entropy must be positive
• if entropy change in system is negative: change is surrounding must be positive and as large as syst to be feasible
• equilibrium: the total entropy change is zero there is no net change in either direction
• small and postive total entropy


  feasible
• large total entropy


  spontaneous reaction
• solubility: the minimum amount of solid that will dissolve in a certian solvent moldm-3
• gdm-3


  divide moldm-3 by mr
• saturated


  adding extdra solid doesnt affect rate of reaction
• Ksp: when a sparingly soluble solid is dissolved in H2O to give a saturated solution
• if Ksp > the ions multiplied together: ions stay in solution
• if Ksp given < ions multiplied together: precipitate is formed
• Ksp units


  moldm-3 same as Kc and other constants
• Bronsted-Lowry acid


  proton donor
• Bronsted-Lowry base


  proton acceptor
• strong acids/bases: almost completely dissociate in H20 release a lot of H+
• weak acids/ bases: Dissociate partially in water/solution forms equilibrium which lies for to the left
• conjugate acid-base pair: consists of two substances related to each other by the donating and accepting of a single hydrogen ion