C3

• Chemical symbol


  Used to write the formulae of elements and simple covalent and ionic compounds
• Writing formulae for simple ionic compounds

  Balance the charges of the ions involved
• Writing formulae for simple covalent compounds

  Imagine what the ion would be, e.g. H2O balances - because the ions would be 2H+ and O2- (and ++ cancels out with -)
• Endothermic reaction


  A reaction that takes in energy from the surroundings so the temperature of the surroundings decreases
• Balanced chemical equation


  Count up how many atoms of each element you have on both sides of the equation, use large numbers e.g. 3H2O to balance the equation so that there is the same amount of each element on each side
• Exothermic reaction


  A reaction that transfers energy to the surroundings so the temperature of the surroundings increases
• Use the names and symbols of common elements from a supplied periodic table to write formulae and balanced chemical equations where appropriate
• Exothermic reactions


  • Combustion
  • Many oxidisation reactions
  • Neutralisation
• Oxidation


  Gain of oxygen
• Ion


  Atoms of elements that have either lost or gained one or more electrons
• Endothermic reactions


  • Thermal decomposition
  • Reaction of citric acid and sodium hydrogencarbonate
• Reduction


  Loss of oxygen
• Everyday examples of exothermic reactions

  • Self-heating cans (e.g. for coffee)
  • Hand warmers
• Oxidation


  Loss of electrons
• Atoms form ions


  In order to have a stable arrangement of electrons - i.e. one similar to that of a noble gas, with 8 electrons in its outer shell
• Cathode


  Metals (or hydrogen) are formed here in electrolysis using inert electrodes
• Everyday examples of endothermic reactions


  • Sports injury packs
• Charges of ions in a compound

  Have to balance out, e.g. HCl exists because of the formation of an H+ ion and a Cl- ion, also H2SO4 exists because of the formation of 2H+ ions and a SO42- ion
• Reduction


  Gain of electrons
• Anode


  Non-metals are formed here in electrolysis using inert electrodes
• Common ions


  • Group 1: form 1+ ions
  • Group 2: form 2+ ions
  • Group 3: form 3+ ions
  • Group 5: form 3- ions
  • Group 6: form 2- ions
  • Group 7: form 1- ions
  • Ions from common acids: NO3- (nitric acid), Cl- (hydrochloric acid), SO42- (sulfuric acid)
• Activation energy


  Minimum amount of energy that particles must have to react
• OIL RIG stands for Oxidation Is Loss and Reduction Is Gain (of electrons)
• Movement of ions in the electrolyte

  1. Positive ions (cations) move to negative electrode to receive electrons and are reduced

  2. Negative ions (anions) move to positive electrode to lose electrons and are oxidised
• Constructing balanced ionic equations (HT only)

  1. Write out the full chemical equation

  2. Split (aq) substances up into ions e.g. HCl(aq) becomes H+(aq) + Cl-(aq) and write out as another equation

  3. Cancel out 'spectator ions' - unchanged ions on either side of the chemical equation

  4. You are now left with the ionic equation
• Acids


  Form hydrogen ions when they dissolve in water
• Chemical reactions


  1. Reacting particles collide with each other

  2. Reacting particles have sufficient energy
• Molten ionic compounds


  Much simpler to predict the products of electrolysis as there are no ions present except those in the ionic compound
• State symbols


  (s) means solid, (l) liquid, (g) gas and (aq) aqueous
• Predicting products of electrolysis of molten ionic compounds

  1. Identify which ions are present

  2. The + ions will go to the cathode

  3. The - ions will go to the anode
• Alkalis


  Contain hydroxide ions
• Reaction profiles


  • Show the relative energies of reactants and products
  • Show the activation energy
  • Show the overall energy change of a reaction
• Mole


  The amount of substance, the number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant: 6.02 x 10^23 per mole
• Neutralisation


  Acid reacting with alkali or a base to form a salt plus water
• The arrow in a reaction profile shows the overall energy change
• Relative formula mass


  The mass of one mole of a substance in grams is numerically equal to its relative formula mass
• Electrolysis of aqueous solutions of ionic compounds


  • Solution contains: the ions that make up the ionic compound, and the ions in water (OH- and H+)
  • Hydrogen (from H+ in water) is produced UNLESS the + ions in the ionic compound are from a metal less reactive than hydrogen
  • Oxygen (from OH- in water) will be produced UNLESS the ionic compound contains halide ions (Cl-, Br-, I-)
• Activation energy


  The energy needed for a reaction to occur
• H+ + OH- → H2O is the ionic equation for any reaction of an acid with an alkali (soluble base)
• One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance