Use these practicals to develop student understanding of energetics and develop research skills
Knowledge of energetics can help understand the process of a reaction and the conditions under which it operates. It also develops knowledge of the link between individual bond energies and the net energy gain or loss as well as the realisation that energy is not just heat. This programme is designed to develop students understanding of energetics as well as developing thinking and research skills.
What is included?
The different activities are designed to improve a number of skills including practical work/dexterity, thinking/analysis skills, literacy, research activities, use of models and teamwork. Students should also gain confidence through the activities and improve the ability to express themselves using scientific language.
|Topic||Type of activity||Timing (mins)||Page ref.|
|Heating copper(II) sulfate||Practical||30||6|
|Endothermic solid-solid reaction||Demonstration||10||15|
|Spontaneous exothermic reaction||Demonstration||10||17|
|Exothermic or endothermic||Practical||30||18|
|Measuring heat energy of fuels||Practical||60||24|
|Diagnostic test||Summative assessment||20–40||31|
Heating copper(II) sulfate
The first activity looks at a reversible reaction and how the energy gain or loss is affected by the change in direction. It introduces the concept of exothermic and endothermic reactions with a colourful example. It also acts to illustrate water of crystallisation and at a higher level it can be used to develop the idea of ligands.
Endothermic solid-solid reaction
This dramatic demonstration looks more carefully at the endothermic process using an example that can fall to -30°C. It offers extension activities through discussion as to how two solids can react together to form a ‘liquid’ (actually a solution/suspension) and a gas. It again brings in the idea of water of crystallisation as well as the rearrangement of substance upon reaction. There is even the opportunity to illustrate how to test for ammonia (alkaline gas and its reaction with concentrated hydrochloric acid).
Spontaneous exothermic reaction
The reaction between potassium manganate(VII) and glycerol is spontaneous as the activation energy is less than the ambient energy at room temperature and therefore it does not require energy to activate the reaction. It is also a good example of the reaction between an oxidising agent and a fuel as well as linking to the change in colour of the manganate with a change in oxidation state. It therefore links to many levels in the curriculum.
Exothermic or endothermic: measuring energy transfers in a range of reactions
Chemical changes are always accompanied by changes in the energy content of the materials that are reacting, and the change is usually observed in the form of heat. Indeed, in many cases the change in temperature when substances react is the only evidence that a chemical reaction has taken place. Students explore develop their skills of observation over several reactions.
Measuring heat energy of fuels
An investigation looking at the varying amount of energy produced by the combustion of a range of alcohols. The practical results are then compared to calculated theoretical values. Heat energy of fuels is a broad ranging investigation that develops the research and evaluation skills of students. It also introduces quantitative calculations.
It is important that students realise that energy can be absorbed or released in different forms such as light and pressure as well as heat. It is always worth a discussion about the heat, light and sound produced by an exploding hydrogen/oxygen balloon. The chemiluminescent example helps to reinforce this fact.
Acts as a summative test to explore the level and knowledge of the topic.
The RSC would like to thank Tim Jolliff for the use of his materials in these resource