Energy from Chemicals (Topic: 5)

(a) describe the meaning of enthalpy change in terms of exothermic (ΔH negative) and endothermic
(ΔH positive) reactions
(b) *represent energy changes by energy profi le diagrams, including reaction enthalpy changes and
activation energies (see 6.1(c))
(c) describe bond breaking as an endothermic process and bond making as an exothermic process
(d) *explain overall enthalpy changes in terms of the energy changes associated with the breaking and
making of covalent bonds
(e) describe combustion of fuels as exothermic, e.g. wood, coal, oil, natural gas and hydrogen
(f) describe hydrogen, derived from water or hydrocarbons, as a potential fuel for use in future, reacting
with oxygen to generate electricity directly in a fuel cell (details of the construction and operation of a
fuel cell are not required) and discuss the advantages and disadvantages of this
(g) name natural gas, mainly methane, and petroleum as sources of energy
(h) describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional
distillation
(i) name the following fractions and state their uses
(i) petrol (gasoline) as a fuel in cars
(ii) naphtha as feedstock for the chemical industry
(iii) paraffi n (kerosene) as a fuel for heating and cooking and for aircraft engines
(iv) diesel as a fuel for diesel engines
(v) lubricating oils as lubricants and as a source of polishes and waxes
(vi) bitumen for making road surfaces
(j) describe photosynthesis as the reaction between carbon dioxide and water in the presence of
chlorophyll, using sunlight (energy) to produce glucose and explain how this can provide a renewable
energy source.