Chem module 3

• First ionisation energy


  the amount of energy required to remove 1 mol of electrons from 1 mol of gaseous atoms
• First ionisation energy examples

  . Na -> Na+ + e-

  . O -> O+ + e-
• ionisation energy trend

  • groups= decreases down a group
  • periods= increases across a period
• trends down a group

  • nuclear charge -> increase
  • atomc radius -> decrease
  • shielding -> stays the same
• Trends down a group

  • increased distance as theres more electron shells
  • increased shielding due to more filled inner shells
  • even though there are more protons, outer electrons are less attracted to nucleus
• Explaining ionisation energies across a period

  • increased nuclear charge as extra proton
  • electron added to same shell
  • atomic radii decreases
  • overall greater attraction between outer electron and nucleus
• Hess's law 


  Total enthalpy change for a chemical reaction is independent of the route by which reaction takes place.
• combustion+ bond enthalpy 


  +A+B-C-D
• formation 


  -A-B+C+D
• • enthalpy change of combustion - away
  • enthalpy change of formation - towards
  • bond enthalpy - away
• Enthalpy 


  energy stored in a chemical system. We can measure the change in this by seeing if the temperature of a reaction changes.
• positive temp change = endothermic

  negative temp change= exothermic
• exothermic reactions


  give out energy to surroundings

  .making bonds - releases energy
• endothermic reaction


  take in energy from surroundings

  .breaking bonds - requires energy
• enthalpy change of neutralisation


  .Enthalpy change when one mole of water is formed from a neutralisation reaction.
• Enthalpy change formation 


  . enthalpy change when one mole of a compound is formed from its elements in their standard state
• Enthalpy of combustion 


  . enthalpy change when one mole of a substance reacts completely with oxygen
• nucleophiles

  • nucleus loving species typically have a negative charge
  • Non-bonding electron pair available for making a new bond
• electrophiles

  • electron loving species typically have an atom with a positive charge
  • have an electron withdrawing
• Rate of reaction 


  the change in concentration of a reactant or product per unit time
• Find rate of reaction on graph with tangent
• Increasing rate of reaction

  • increasing pressure
  • increase surface area
  • increasing temperature
  • adding a catalyst
  • increasing concentration
  • more successful frequent collisions
• Equilibrium constant Kc


  aA + bB -> cC + dD

  kKc=[C]c[D]d/[A]a[B]b

  ^square brackets refer to concentration
• • Kc higher than 1 - equilibrium lies right
  • Kc lower than 1 - equilibrium lies left
• CoCl2->Co + Cl2

  • decreasing conc of CO - moves left
  • increasing pressure -moves left
  • increasing temp - moves right (endothermic side)
• Effect of concentration


  equilibrium moves to side with more products
• effect of pressure


  moves to side with fewer gas molecules
• effect of temp


  increase temp -> moves endothermic

  decrease temp -> moves to exothermic
• effect of catalyst 


  no effect
• importance of catalysts

  • allow lower temps to be used
  • reduces fossil fuels
  • less CO2 - reaction more sustainable
• heterogenous 


  involves the use of a catalyst in a different state from reactants. Typical examples involved a solid catalyst with a liquid or gas reactant.
• homogenous


  has catalyst in same state as reactants
• test for carbonate ions

  add an acid and see fizzing
• test for sulphate ions 


  Add source of barium ions and see a white precipitate
• test for halide ions

  • add silver nitrate and check colour of precipitate
  • chloride=white
  • bromide=cream
  • iodide=yellow
• Further tests(confirming halide ions)

  • add ammonia
  • silver chloride dissolves in dilute ammonia
  • silver bromide dissolves in concentration ammonia
  • silver iodide doesn't dissolve in either
• Test for ammonium ions

  • add warm sodium hydroxide and test any gas with damp red litmus paper
  • litmus paper turns blue - ammonium ions present
• reactivity of group 2 increases as you go down

  • down the group - more protons
  • outer electrons further from nucleus
  • increased shielding from extra shells inbetween - less nuclear attraction
  • easier to lose an electron/form a positive ion
• Group 2 reactions

  • 2M + O2 -> 2MO (metal oxide)
  • M + 2H2O -> M(OH)2 + H2 (Metal hydroxide)
  • M + 2HCL -> MCL2 + H2 (salt + hydrogen)
• Explaining ionisation energy across a period

  • increased nuclear charge as extra proton
  • electron added to same shell
  • atomic radii decreases
  • overall greater attraction between outer electron and nucleus