Higher chemistry paper 1

• The atoms that go in must come out in a chemical reaction, so we must balance equations
• Relative formula mass


  The sum of the relative atomic masses of the atoms in a compound
• Some reactions produce a gas product which, if it leaves the reaction vessel, will result in a seeming decrease in mass of the reactants
• Mole


  A specific number of atoms or molecules, used as a way of comparing amounts of substances
• One mole


  The amount of a substance that has a mass equal to its relative atomic or formula mass in grams
• To balance a chemical equation, the number of moles of reactants and products must be equal
• Calculating mass of product from mass of reactant

  Mass -> Moles -> Moles -> Mass
• Stoichiometry


  The ratio of moles of one substance to another in a reaction
• The limiting reactant in a reaction is the one that runs out first
• Concentration of a solution

  Expressed in moles per decimeter cubed
• Percentage yield is the amount of product actually made compared to the theoretical maximum
• One mole of any gas takes up a volume of 24 dm^3 at room temperature and pressure
• Reactivity series of metals

  • Hydrogen
  • Carbon
  • Most reactive metals
  • Least reactive metals
• Displacement reaction


  A more reactive metal displaces a less reactive metal from a compound
• Reduction


  The gain of electrons by a reactant
• Oxidation


  The loss of electrons by a reactant
• Metals more reactive than hydrogen can displace it from acids
• Alkalis (pH > 7) react with acids (pH < 7) to produce a salt and water
• Dissociation


  The partial separation of ions when a substance dissolves in water
• pH scale


  A logarithmic scale that measures the concentration of H+ ions in a solution
• Strong acid


  An acid that dissociates completely in solution
• Weak acid


  An acid that only partially dissociates in solution
• Titration


  Measuring the concentration of an acid or alkali by reacting it with a solution of known concentration
• In electrolysis, positive metal ions (cations) are reduced at the cathode, and negative ions (anions) are oxidized at the anode
• Electrolysis can be used to extract and purify metals from their ores
• Exothermic reaction


  A reaction that releases more energy than it absorbs
• Endothermic reaction


  A reaction that absorbs more energy than it releases
• Measuring energy changes in a reaction

  Carry out a neutralisation reaction in an insulated container and measure the maximum temperature change
• Energy profile


  A diagram showing the energy changes in a reaction, including activation energy
• Battery/fuel cell


  A device that produces a potential difference (voltage) from chemical reactions
• Non-rechargeable batteries stop working when the reactants are used up, while rechargeable batteries can be recharged
• the reactivity series is the relative ability of metals to displace other metals from their compounds