Research this Simple endothermic and exothermic reactions are used in the making of heat packs and ice packs. Research the chemical reactions that take place. What features of the packs make them suited to their purpose? Are there any safety concerns connected with their use?
Activation energy The minimum energy needed for a reaction to take place.
Activation energy When reactions take place, atoms rearrange to form new compounds. However, reactions sometimes need energy to start to react. This energy is called the activation energy. When wood burns, energy is released. This energy is felt as heat. However, when burning a
wooden splint, even though the reaction is exothermic the splint must be held in the Bunsen burner flame for a number of seconds before it ignites. The Bunsen flame supplies the energy that is required for the reaction to begin. The splint continues to burn, away from the Bunsen flame, once the reaction starts. The Bunsen flame supplies the activation energy.
Energy profile diagrams An energy profile diagram is a way of representing the energy changes in a chemical reaction on a graph. The x-axis is time and the y-axis is the energy of the reaction.
Activation energy Reactants
Energy released in the reaction
Products Reaction
Fig. 11 Energy profile diagram for an exothermic reaction.
Reaction
Fig. 12 Energy profile diagram for an endothermic reaction.
Both Fig. 11 and Fig. 12 show that more energy is needed to start the reaction. This is the activation energy and it is shown as a bump on the energy profile diagram. Fig. 11 shows the energy profile diagram for an exothermic reaction. The energy of the
reactants is higher than the energy of the products. When this reaction takes place the extra energy is lost as heat which warms up the container. Fig. 12 shows the energy profile diagram for an endothermic reaction. The energy of the reactants is less than the energy of the products. When this reaction takes place the extra energy needed is taken in from the surroundings and it feels colder.
