Higher Chemistry Unit 1

Reaction rates
1. Affected by
  1. temperature
    1. the average kinetic energy of the particles in a substance
      1. an energy distribution diagram could be useful
        only the particles in the shaded area have enough energy to collide successfully
  2. concentration
    1. increasing concentration causes more collisions
  3. particle size
    1. the bigger the surface area the faster the reaction
  4. catalysts
    1. speed up chemical reactions
    2. two types
      1. homogeneous
        same physical state as reactants
      2. heterogeneous
        different physical state to reactants
        ADSORB reactant molecules onto active site surfaces
    3. catalytic poisons bond so firmly to active sites there are no sites for reactant molecules
    4. form an alternative activated complex
      1. therefore provides an alternative reaction pathway
    5. catalysts in industry
      1. iron
        used in haber process to make ammonia
      2. platinum
        used in oxidation of ammonia to nitrogen dioxide in ostwald process
      3. nickle
        used to hydrogenate vegetable oils in the manufacture of margarine
      4. zymase
        used in brewing
      5. vanadium oxide
        used in contact process to make sulphuric acid
      6. aluminium oxide
        used in catalytic cracking
        turns long chain alkanes into more useful short chain alkenes
    6. enzymes
      1. biological catalysts
      2. large soluble protein molecules
      3. works best at an optimum temperature and pH
        optimum temperature in human bodies is 37*C
      4. can be denatured (changes shape) at too high temperatures or pH's
  5. collisions
    1. may form an activated complex
    2. for a chemical reaction to occur, reactant particles must collide
    3. to increase reaction rate, number of successful collisions must be increased
      1. Activation energy is the minimum kinetic energy needed for a successful collisiom
        the difference between the energies of the activated complex and the reactants.
        highly unstable dpecies formed during a reaction as old bonds break and new bonds form
        the minimum energy needed to form an activated complex
        Activated complex is the minimum energy needed to cause a chemical reaction
2. 1/t
  1. measured in s-1
Enthalpy
1. combustion
  1. the energy released during complete combustion of one mole of oxygen
2. neutralisation
  1. the energy change when an acid an alkali cancel each other out to form one mole of water
3. solution
  1. the energy change when one mole of substance dissolves in water
4. heat intake/outtake
  1. exothermic
    1. gives out heat energy because energy is released to surroundings
    2. products have LESS energy than reactants
    3. ΔH is negative
  2. endothermic
    1. takes in heat energy because energy is absorbed from surroundings
    2. products have MORE energy than reactants
    3. ΔH is posit8ive
5. cannot be measured directly
  1. we can only measure the change in energy
    1. ΔH
6. potential energy diagrams
Patterns in the Periodic Table
1. elements in the same group have same number of outer electrons; similar chemical properties
2. as you go along a period , an additional proton is added to the nucleus
3. covalent radii
  1. along a period atoms get SMALLER
    1. increasing number of protons in nucleus attract the electrons more strongly pulling them inwards
  2. down a group atoms get BIGGER
    1. there are more electron shells
4. ionisation energy
  1. INCREASE along a period
    1. increasing nuclear charge makes it harder to remove electrons
  2. DECREASES down a group
    1. outer electrons are further from the nucleus and are screened from nuclear attraction y more inner electron shells
  3. the energy needed to remove one mole of electrons from one mole of atoms
5. electronegativity
  1. a measure of the ability to attract electrons in a bond
  2. elements at the top right of the table are very electronegative
  3. elements a the bottom left are the least electronegative
Bonding, Structure, properties
1. we can use electronegativity to make predictions about the bonding between atoms
  1. IONIC = very different electronegativites
  2. COVALENT = very similar electronegativities
  3. POLAR = fairly different electronegativites
2. metalls
  1. delocalised outer electrons are free to leave the metal atoms
3. elements
  1. nonmetals
    1. pure covalent bonding, atoms have identical electronegativities
4. structure
  1. discrete covalent
    1. sulphur
      1. S8
    2. phosphorus
      1. P4
5. intermolecular/intramolecular
  1. intermolecular
    1. hydrogen bonding
      1. polar bonds formed between hydrogen and fluorine, nitrogen or oxygen
      2. strongest of the intermolecular bonds
      3. raises the boiling point
    2. bonding BETWEEN molecules
    3. van der waals forces
      1. molecules become temporarily polar due to a momentary lack of symmetry in the electrons
  2. intramolecular
    1. bonding WITHIN molecules
    2. covalent bonding
The Mole
1. relative formula mass
2. contains 6.02x10^23 particles
3. volume
  1. approximately 24L unless stated otherwise
Calculations
1. enthalpies
  1. combustion
    1. ethanol
  2. solution
  3. nutralisation
PPA's
1. PPA 1
  1. effect of concentration on reaction rate
    1. H2O2 + 2H(+) + 2I(-) ----> 2H2O + I2
    2. sharp colour change
      1. starch turns black to blue
2. PPA 2
  1. effect of temperature on reaction rate
    1. 5(COOH)2 + 6H(+) + 2MnO4(-) ----> 2Mn(2+) + 10CO2 + 8H2O
    2. acidified potassium permanganate = purple to colourless
    3. all experiments identical except for twmperature
    4. evaluation
      1. dry beakers to avoid affecting concentrations
      2. accurate experiment not possible at room temperature due to gradual colour change
3. PPA 3
  1. enthalpy of combustion of ethanol

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Higher Chemistry Unit 1

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