The heat of reactions is recorded in Joules since heat is a type of energy. When chemicals react they involve the transfer of energy heat. This transfer can result in the heating exothermy or the cooling endothermy of the product. Exothermic reactions are ones that liberate heat energy. The excess heat in the reaction is the result of the formation of new bonds in the products. Bell Ringer: Balance the following equations Introduction: 20 minutes Light a sparkler and ask: What is happening?
Is this reaction using energy or producing energy? How can you tell? A simple sparkler contains potassium perchlorate, aluminum and dextrin. The KClO 4 provides the oxygen to cause a fire, dextrin a sugar provides the fuel and is also a binder to hold the whole thing together, and aluminum creates the bright shimmering sparks. Can you think of other processes that produce energy in the form of heat? Remember from our last chapter that in chemical reactions, bonds are broken, atoms are rearranged, and new bonds are formed.
Bond breaking requires energy and bond formations releases energy. Almost all chemical reactions either absorb or release energy. Reactions that release heat, like sparklers are called exothermic reactions. It releases heat to its' surroundings. The opposite of an exothermic reaction is a reaction that absorbs heat.
Reactions than absorb heat are called endothermic reactions. Activity: 40 minutes to model materials usage, read procedure, gather supplies, perform experiments, collect data, put away supplies and answer questions. Make sure students put on goggles and aprons before conducting this group activity. Groups should be students. Give each student their own lab worksheet and table to fill out. Reinforce: 20 minutes Use transparency during discussion Endothermic Reactions A camping stove uses oxygen from the air and a fuel such as propane to heat food and water.
The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants. This stored chemical energy, or heat content, of the system is known as its enthalpy. Exothermic reactions release heat and light into their surroundings. For example, combustion reactions are usually exothermic.
In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction. This means that the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products. Excess energy from the reaction is released as heat and light. For example, decomposition reactions are usually endothermic.
0コメント