Energy and Chemical Change

This chemistry extension module from the Salters’ Science course deals with the energy changes which accompany chemical reactions. Photosynthesis is considered as the fundamental source of energy to sustain life process, and respiration as the mechanism for coupling the energy to body processes. ‘Calorific values’ of food are compared to experimental measures of the energy released when they are burned. Fermentation and uses of ethanol are studied. Simple cells are studied as examples of conversion of chemical energy to electricity, with revision of the reactivity series for metals. A variety of electrolysis experiments lead to discussion of fuel cells and photovoltaic cells. Endothermic and exothermic reactions are studied in relation to the energy transfers in bond-making and bond-breaking and activation energy. Patterns of covalent and ionic bonding are related to the positions of elements in the Periodic Table. Characteristics of free radicals are described, with applications to dental amalgams and in relation to the life-protecting effect of the ozone layer.

1: Catching sunlight
Basic ideas about photosynthesis are revised. Students extract chlorophyll and relate its absorption spectrum to its function in trapping solar energy.

2: Fuel for the body
Students measure the energy transfer when burning a food. This is related to the ‘dietary value’ of foods and the release of energy by cellular respiration.

3: Getting the energy out
The formation of fossil fuels is revised. Students investigate conditions needed for fermentation and consider ethanol as a fuel.

4: Electricity and chemical change
Simple electrochemical cells are used to obtain electrical energy from chemical change, and related to the reactivity series of metals and the Periodic Table.

5: Electricity strikes back!
The use of electricity to produce chemical change is demonstrated for electrolysis of salt and of acidified water. Students experiment with electroplating copper.

6: Fuelling the future
Simple fuel cells are demonstrated. Photovoltaic cells are also demonstrated as a way of converting sunlight to electrical energy. Text exercises develop ideas about overall energy strategies for a community.

7: Energy ups and downs
Students explore a variety of exothermic and endothermic reactions. The concept of activation energy is introduced. Energy level diagrams are introduced as a way of showing energy level changes during chemical reactions.

8: Linking atoms together
A card-game simulation revises formation of ionic and covalent bonds and relates them to the positions of elements in the Periodic Table. Practical work on the light-initiated setting of dental amalgam introduces free radicals. The formation and action of the ozone layer are discussed.